fluids, electrolytes, and nutrition - accp
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Fluids, Electrolytes, and Nutrition
ACCP Updates in Therapeutics® 2012: The Pharmacotherapy Preparatory Review and Recertification Course
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Fluids, Electrolytes, and Nutrition
Judith L. KristELLEr, Pharm.d., BCPsWilkes university
Wilkes-Barre, Pennsylvania
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Learning Objectives:
1. Calculatetheosmolarityofintravenousfluidsandcompare with normal plasma osmolarity.
2. Recommendanappropriateintravenousfluidregi-men and monitoring parameters based on a pa-tient’s clinical characteristics.
3. Discusstheappropriateuseandrisksofhypertonicandhypotonicsaline,andrecommendatreatmentregimenandmonitoringparameterstoensuresafeandeffectiveuseoftheseintravenousfluids.
4. Assess electrolyte abnormalities and recommendanappropriatepharmacologictreatmentplanbasedonindividualpatientsignsandsymptoms.
5. Discussappropriate indicationsfor theuseofen-teralandparenteralnutrition(ENandPN).
6. Recommend a patient-specificEN formula, infu-sionrate,andmonitoringparameters.
7. Recommend a patient-specific PN formula andmonitoringplanbasedonthetypeofintravenousaccess,nutritionalneeds,comorbidities,andclini-calcondition.
8. Discussstrategiesforpreventingcomplicationsas-sociatedwithENandPN.
Self-Assessment Questions:Answers and explanations to these questions may be found at the end of this chapter.
1. A 74-year-oldwoman presents to the emergencydepartment with a 3-day history of cough, tem-peratureto102°F,andlethargy.Shehasthefollow-ingvital signsand laboratoryvalues:bloodpres-sure(BP)72/40mmHg,heartrate(HR)115beats/minute,urineoutput10mL/hour,whitebloodcellcount(WBC)18,000,hemoglobin12.5g/dL,bloodureanitrogen/creatinineratio(BUN/Cr)28/1.7mg/dL(baselineCr1.2mg/dL),bloodglucose82mg/dL,andweight72kg.Aftera500-mLfluidbolusof0.9%sodiumchloride (NaCl),herBPandHRare80/46mmHgand113beats/minute.Herchestradiographisconsistentwithpneumonia.Hermed-ical history includes coronary artery disease andarthritis.Whichoneof the following is themostappropriate treatment?A. Furosemide40mgintravenously.
B. 5%albumin500mLinfusedover4hoursplusnorepinephrinetitratedtomaintainasystolicBPof90mmHgorhigher.
C. 1000-mLfluidboluswith5%dextrose(D5W)and0.9%NaCl.
D. 1000-mLfluidboluswith0.9%NaCl.
2. An order has been received for 3%NaCl. Using0.9%NaCland23.4%NaCl,firstdeterminehowmuch of each is necessary to prepare 1L of 3%NaCl. Second, calculate the osmolarity of 3%NaCl.Finally,determinewhethertheresultantso-lutionshouldbeadministeredthroughacentralorperipheralintravenousinfusion(molecularweight[MW]ofNaClis58.5,osmoticcoefficientis0.93).A. Mix907mLof0.9%NaClplus93mLof
23.4%NaCl;osmolarity=954mOsm/L;central intravenous infusion.
B. Mix907mLof0.9%NaClplus93mLof23.4%NaCl;osmolarity=477mOsm/L;peripheral intravenous infusion.
C. Mix850mLof0.9%NaClplus150mLof23.4%NaCl;osmolarity=954mOsm/L;central intravenous infusion.
D. Mix850mLof0.9%NaClplus150mLof23.4%NaCl;osmolarity=513mOsm/L;peripheral intravenous infusion.
3. A 68-year-oldman is admitted to the hospital forworseningshortnessofbreathduringthepast2weeksattributabletoheartfailure.HisserumNaconcentra-tiononadmissionwas123mEq/L.Otherabnormallaboratory values include brain natriuretic peptide850andCr1.7mg/dL.Chestradiographisconsis-tentwithpulmonaryedema.Thepatientweighs85kgonadmission,whichisup3kgfromhisbaselineweight.Thepatientisnotexperiencingnausea,head-ache,ormentalstatuschanges.Thephysicianorders3%NaCltotreatthehyponatremia.Whichoneofthefollowingrecommendationsisbest?A. 3%NaClisanappropriatechoicebecausethe
hyponatremiaislikelyacute.B. A250-mLbolusof3%NaClisappropriate
ifusedincombinationwithfurosemidetopreventvolumeoverload.
C. 3%NaClisappropriateaslongastheserumNadoesnotincreasemorethan10mEq/Lin24 hours.
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D. Therisksof3%NaCloutweighthepotentialbenefitforthispatient.
4. A55-year-oldmanwithdiabetesandkidneydis-ease presents with hyperkalemia. His laboratoryvaluesincludepotassium(K+)7.2mEq/L,calcium(Ca)9mg/dL,albumin3.5,andbloodglucose302mg/dL.Hiselectrocardiogram(ECG)isabnormalwithpeakedTwaves.Whichoneofthefollowingisthebestrecommendationforinitialtreatmentofhishyperkalemia?A. Regularinsulin10unitsintravenouslyplus50
gofglucoseintravenously.B. 10%Ca++gluconate10mLintravenouslyover
5 minutes.C. Kayexalate15gmixedwith100mLof20%
sorbitolevery4hoursasneeded.D. Na+bicarbonate50mEqintravenouslyover5
minutes.
5. A 68-year-old patient is admitted to the hospitalafteracardioembolicstroke.Hermedicalhistoryis significant for atrial fibrillation, acutemyocar-dialinfarction,anddiabetes.Shehasbeenuncon-sciousfor48hours.Themedical teamdecides tostartfeedingthepatient.Herweightis60kg,andalllaboratoryvaluesincludingglucoseconcentra-tionsarenormal.Althoughshecurrentlyhasnoen-teralaccess,shedoeshaveaperipheralintravenouscatheter. Which one of the following nutritionalregimensisbestforthispatient?A. Initiateparenteralnutrition(PN)containing
60gofaminoacids(AA),500mLof10%lipidemulsion,300gofdextrose,standardelectrolytes,multivitamins,andtraceelementsinavolumeof2000mLadministeredover24hours.
B. InitiatePNcontaining40gofAA,500mLof10%lipidemulsion,200gofdextrose,standardelectrolytes,multivitamins,andtraceelementsinatotalvolumeof2000mLadministeredover24hours.
C. Insertanasogastric(NG)ornasoduodenalfeedingtubeandinfuseIsocal(1kcal/mL)startingat25mL/hourandadvancetoagoalrateof65mL/hour.
D. InsertapercutaneousendoscopicgastrostomyfeedingtubeandinfuseIsocal(1kcal/mL)startingat25mL/hourandadvancetoagoalrateof100mL/hour.
6. A70-year-oldmanisadmittedtothehospitalwithperitonitis caused by severe inflammatory boweldisease.Thepatienthasreceivedadequatefluidre-suscitation,andheisprescribedappropriateantibi-otics.Thephysicianwantsthepatienttohavesev-eraldaysofbowelrest,andheorshehasconsultedthepharmacisttorecommendaPNformulatobeadministeredthroughacentralline.Thepatientishemodynamically stable, with normal electrolyteconcentrations. Weight is 55 kg, prealbumin 20mg/dL,BUN/Cr20/1.1mg/dL,andWBC17,000.Assumingthatappropriateelectrolytes,multivita-mins,andtraceelementsareincluded,whichoneof the followingPNformulaswhenadministeredover 24 hours will provide this patient adequatecalories,AA,andlipid?A. AA10%700mL,dextrose30%325mL,lipid
20%500mL.B. AA10%450mL,dextrose70%400mL,
lipid10%500mL.C. AA10%800mL,dextrose70%350mL,lipid
10%500mL.D. AA15%900mL,dextrose50%500mL,
lipid10%500mL.
7. A59-year-oldmanhasbeenadmittedtothehospi-talafterseveraldaysofvomitinganddiarrhea.Intheemergencydepartment,hehadseveralrunsofnonsustained ventricular tachycardia.His plasmaK+onadmissionwas2.8mEq/L.After receiving200mEqofpotassiumchloride(KCl)infusedover24hours,hisrepeatK+is3.2mEq/L,andhecontin-uestohaverunsofventriculartachycardia.OtherlaboratoryvaluesincludeNa+143mEq/L,magne-sium1.4mg/dL,phosphorus3mg/dL,Ca++9mg/dL,andionizedCa++1.1mmol/L.Whichoneofthefollowingsuggestionsisbesttotreatthispatient’shypokalemia?A. AdministerKCl20mEqintravenouslyover1
houreach×4dosesandrecheckK+.B. Administermagnesiumsulfateasa2-gslow
intravenous infusion.
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C. AdministerK+ phosphate 15 mmol intravenously over 4 hours.
D. AdministerCa++gluconate2gintravenouslyover 5 minutes.
8. Which one of the following nutritional strategiescan prevent gutmucosal atrophy and subsequentbacterialtranslocation?A. PNenrichedwithglutamine.B. PNenrichedwithbranched-chainAA.C. Enteralnutrition(EN).D. Zinc supplementation.
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I. FLuId mAnAgement
A. Distributionoftotalbodyfluid(TBF).
75%ofextracellularfluidisinterstitial(thisfluid“bathesthecells”andis
separatedfromintravascularspacebythesemipermeablecapillarymembrane)
25%ofextracellularfluidisintravascular(about5Lofbloodvolume)
40%ofTBFisextracellular
60%ofTBFis intracellular (enclosedbythecellmembrane)
Figure 1.Distributionoftotalbodyfluid(TBF).
1. Estimatedas60%ofleanbodyweight(LBW)inmenand50%inwomen;anormaladulthasabout42Loffluid
2. Totalbodywaterisfurtherdividedintointracellular(IC)spaceandextracellular(EC)space.a. Around60%ofTBFisIC,and40%isEC;theICandECfluidcompartmentsareseparatedby
thecellmembranes,whicharehighlypermeabletowater.b. TheECcompartmentisfurtherdividedintotheinterstitial(IS)spaceandtheintravascularspace;
theISandintravascularfluidcompartmentsareseparatedbythecapillarymembrane,whichispermeabletoalmostallsolutesexceptproteins.i. Seventy-fivepercentoftheECfluidisintheISspace.ii. Twenty-fivepercentoftheECfluidisintheintravascularspace;theECfluidinthe
intravascularspaceisknownasplasmaandconsistsofabout3L;ifyoualsoconsiderabout2Loffluidfoundinredbloodcells(thus,ICfluid),thetotalbloodvolumeisaround5L.
3. TheapproximatedistributionofTBFintotheICandECcompartmentswithfurtherdistributionoftheECfluidintotheISandintravascularcompartmentsisimportanttorememberfordeterminingthedistributionofintravenousfluid.
B. DistributionofIntravenousFluid1. Crystalloidsareintravenousfluidsthatcancontainwater,dextrose,Na+,Cl-,andotherelectrolytes.
LactatedRinger’s(solution)(LR)isacrystalloidthatcontainsmostlyNa+andCl-,butalsolactate,K+,andCa++.a. SodiumandCl-donotfreelycrossintocells,buttheywilldistributeevenlyintheECspace.b. For0.9%NaClorLR,only25%willremainintheintravascularspace,and75%willdistributein
theISspace;therefore,when1Lof0.9%NaClorLRisadministered,about250mLoffluidwillremain in the intravascular compartment.
2. “Free”waterisequivalenttoD5W.a. D5Wismetabolizedtowaterandcarbondioxide.b. Watercancrossanymembraneinthebody;therefore,itwillbeevenlydistributedinTBF(“free”
becauseitisfreetocrossanymembrane).i. ManyexpertsavoidtheadministrationofD5Wwheneverpossibleinpatientswithelevated
intracranialpressure(ICP)becauseitcancrossintocerebralcells,causingafurtherelevationinICP.
ii. SomepractitionersavoidtheuseofD5Wbecauseoftheriskofhyperglycemia,eventhoughD5Wcontainsonly5gofdextrose/100mL,whichisequivalentto17kcal/100mL.
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c. For D5W,60%willdistributetotheICspaceand40%totheECspace.Ofthe40%distributedtotheECspace,25%willremainintheintravascularspace,and75%willdistributetotheISspace.Therefore,when1LofD5Wisadministeredintravenously,about100mLoffluidwillremaininthe intravascular compartment.
3. Colloidsincludepackedredbloodcells,pooledhumanplasma(5%albumin,25%albumin,5%plasmaproteinfraction),semisyntheticglucosepolymers(dextran),andsemisynthetichydroxyethylstarch(hetastarch),a. Colloidsaretoolargetocrossthecapillarymembrane;therefore,theywillprimarilyremainin
theintravascularspace(althoughasmallportionwill“leak”intotheISspace).b. Exceptfor25%albumin,administering500mLofcolloidwillresultina500-mLintravascular
volumeexpansion.c. Because25%albuminhasanoncoticpressureabout5timesthatofnormalplasma,itwillcausea
fluidshiftfromtheISspaceintotheintravascularspace.Forthisreason,100mLof25%albuminwillresultinabout500mLofintravascularvolumeexpansion.Thishyperoncoticsolutionshouldgenerallybeavoidedinpatientsrequiringfluidresuscitation,becausealthoughtheintravascularspacewillbeexpanded,fluidwillshiftoutoftheISspace,potentiallycausingdehydration.Itmaybeusefulinpatientswhodonotrequirefluidresuscitationbutwhocouldbenefitfromaredistributionoffluid(e.g.,ascites,pleuraleffusions).
d. Hydroxyethylstarchanddextranproductshavebeenassociatedwithacoagulopathyandthereforeshouldbeavoidedinpatientsatincreasedriskofhemorrhage(e.g.,activebleeding,increasedriskofbleeding,kidneydisease).
table 1.DistributionofIntravenousFluid
Intravenous Fluid Infused Volume (mL)equivalent Intravascular Volume expansion (mL)
NS 1000 250LR 1000 250D5W 1000 100Albumin5% 500 500Albumin25% 100 500Hetastarch6% 500 500
D5W=5%dextrose;LS=lactatedRinger’s(solution);NS=normalsaline.
C. FluidResuscitation1. Intravascularfluiddepletioncorrelateswithreducedcardiacfunctionandorganhypoperfusion.2. Signsorsymptomsusuallyoccurwhenaround15%(750mL)ofbloodvolumeislost(e.g.,
hemorrhage)orshiftsoutoftheintravascularspace(e.g.,severesepsis).3. Fluidresuscitationisindicatedforpatientswithsignsorsymptomsofintravascularvolumedepletion.
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table 2.Signs/SymptomsofIntravascularVolumeDepletion
Tachycardia(>100beats/minute)Hypotension(SBP<80mmHg)OrthostaticchangesinHRorBPIncreasedBUN/Crratio>10:1DrymucousmembranesDecreasedskinturgorReducedurineoutputDizzinessImprovementinHRandBPaftera500-to1000-mLfluidbolusBP=bloodpressure;BUN=bloodureanitrogen;Cr=creatinine;HR=heartrate;SBP=systolicbloodpressure.
4. Thegoaloffluidresuscitationistorestoreintravascularvolumeandpreventorganhypoperfusion.5. Becauseintravascularvolumedepletioncancauseorgandysfunctionanddeath,promptresuscitation
is necessary.a. Intravenousfluidsareinfusedrapidly,preferablythroughacentralvenouscatheter.b. Intravenousfluidsareadministeredasa500-to1000-mLbolus,afterwhichthepatientis
reevaluated;thisprocessiscontinuedaslongassignsandsymptomsofintravascularvolumedepletionareimproving.
6. Crystalloids(0.9%NaClorLR)arerecommendedforfluidresuscitation.a. LRishistoricallypreferredinsurgery/traumapatients,butnoevidencesuggestssuperiorityover
NSforfluidresuscitation.b. ThelactateinLRismetabolizedtobicarbonateandcantheoreticallybeusefulformetabolic
acidosis;however,lactatemetabolismisimpairedduringshock.Thus,itmaybeanineffectivesourceofbicarbonate.
7. Colloidshavenotbeenshowntobesuperiortocrystalloidsandareassociatedwithaconsiderablyhighercost.Thefollowingareexamplesofmorecommon,althoughcontroversial,usesofcolloids:a. Semisyntheticcolloidsmaybeconsideredafterfluidresuscitationwithcrystalloid(usually4–6
L)hasfailedtoachievehemodynamicgoalsorwhenclinicallysignificantedemalimitsthefurtheradministrationofcrystalloid.
b. Albuminmaybeconsideredinpatientswithanalbuminconcentrationlessthan2.5g/dLwhohaverequiredalargevolumeofresuscitationfluidsandhavearelativecontraindication(i.e.,increasedriskofhemorrhage)forasemisyntheticcolloid.
c. Albumin(theoretically,25%ispreferred)maybeconsideredinconjunctionwithdiureticsforpatientswithclinicallysignificantedema(e.g.,pulmonaryedemacausingrespiratoryfailure)andanalbuminconcentrationlessthan2.5g/dL,whenappropriatelydoseddiureticsareineffective.
D. MaintenanceIntravenousFluids1. Maintenanceintravenousfluidsareindicatedinpatientswhoareunabletotolerateoralfluids.2. Thegoalofmaintenanceintravenousfluidsistopreventdehydrationandmaintainanormalfluidand
electrolytebalance.3. Maintenanceintravenousfluidsaretypicallyadministeredasacontinuousinfusionthrougha
peripheral or central intravenous catheter.4. Commonmethodsofestimatingthedailyvolumeinchildrenandadults
a. Administer100mL/kgforfirst10kg;then50mL/kgforthenext10–20kg(i.e.,1500mLsofar)plus20mL/kgforeverykilogramgreaterthan20kgor
b. Administer20–40mL/kg/day(foradultsonly).c. Adjustfluidsonthebasisoftheindividualpatient’sinput,output,andestimatedinsensibleloss.
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5. AtypicalmaintenanceintravenousfluidisD5Wwith0.45%NaClplus20–40mEqofKClperliter.TheKClcontentcanbeadjustedfortheindividualpatient.
Patient Cases1. A65-year-oldmanwitha3-dayhistoryoftemperatureto102°F,lethargy,andproductivecoughishospital-
izedforCAP.Hismedicalhistoryincludeshypertensionandcoronaryarterydisease.HisvitalsignsincludeHR104beats/minute,BP112/68mmHg,andtemperature101.4°F.Hisweightis80kg,urineoutput10mL/hour,BUN16,Cr1.7mg/dL,andWBC10.4.Otherlaboratoryvaluesarenormal.Whichoneofthefollow-ingismostappropriateatthistime?A. Furosemide40mgintravenously.B. Albumin25%intravenouslyover60minutes.C. Hetastarch6%500mLintravenouslyover60minutes.D. D5W/0.45%NaClplusKCl20mEq/Ltoinfuseat110mL/hour.
2. After2daysofappropriateantibiotictreatment,thepatientinquestion1hasWBCof9,andheisafebrile.HisBPis135/85mmHg,andhisurineoutputisnow45mL/hour.Hisalbuminis3.2,BUN14,andCr1.4mg/dL.Allotherlaboratoryvaluesarenormal.Hisappetiteisstillpoor,andheisnottakingadequatefluids.Hehasperipheralintravenousaccess.Whichoneofthefollowingismostappropriatetoinitiate?A. PeripheralPNtoinfuseat110mL/hour.B. Albumin5%500mLintravenouslyover60minutes.C. D5W/0.45%NaClplusKCl20mEq/Ltoinfuseat110mL/hour.D. LRsolutiontoinfuseat110mL/hour.
II. OSmOLALItY
A. PlasmaOsmolalityIsNormallyBetween275and290mOsm/kg.1. Terminologyclarification
a. Osmolalityisameasureoftheosmolesofsoluteperkilogramofsolvent(Osm/kg),whereasosmolarityisameasureofosmolesofsoluteperliterofsolution(Osm/L).
b. Plasmaosmolarity(mOsm/L)canbecalculatedbythefollowingequation:osmolarity=osmolality×0.995,illustratingthatthereisnoclinicallysignificantdifferencebetweenthem(i.e.,plasmaosmolarityisabout1%lowerthanplasmaosmolality).
2. Plasmaosmolalityismaintainedwithinanormalrangebythirstandsecretionofargininevasopressin(i.e.,ADH)fromtheposteriorpituitary.
3. SodiumsaltsaretheprimarydeterminantofplasmaosmolalityandthereforeregulatefluidshiftsbetweentheICandECfluidcompartments.
4. Plasmaosmolality(inmilliosmolesperkilogram)canbeestimated:(2×Na+)+(glucose/18)+BUN/2.8.
5. Increasesinplasmaosmolalitycauseanosmoticshiftoffluidintotheplasma,resultingincellulardehydrationandshrinkage.
6. Decreasesinplasmaosmolalitycauseanosmoticshiftoffluidintocells,resultingincellularoverhydrationandswelling.
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B. IntravenousFluidsCanBeClassifiedbyTheirOsmolarityRelativetoPlasma.1. Isotonicfluidwillnotresultinafluidshiftbetweenfluidcompartmentsbecausetheosmolarityis
similar to plasma.2. HypertonicfluidcancausefluidtoshiftfromtheICtotheECcompartmentwithsubsequentcellular
dehydrationandshrinkage.3. Hypotonicfluidwithanosmolaritylessthan150mOsm/LcancausefluidtoshiftfromtheECtothe
ICcompartmentwithsubsequentcellularoverhydrationandswelling.a. Redbloodcellswellingcancausecellrupture(i.e.,hemolysis).b. Braincellscanswell,causingcerebraledemaandherniation;thisismostlikelytooccurwith
acutehyponatremia(occurringinlessthan2days).
C. Definitions1. Equivalentweight=MWdividedbyvalence
a. Amilliequivalent(mEq)=1/1000ofanequivalent.b. Examplesofequivalentweight
table 3.ElectrolyteMW,Valence,andEquivalentWeightelectrolyte mW Valence equivalent Weight (g)Sodium 23 1 23Potassium 39 1 39Chloride 35.5 1 35.5Magnesium 24 2 12
MW=molecularweight.
2. Osmoles=numberofparticlesinsolution(assumingcompletedissociation)a. Amilliosmole=1/1000ofanosmole.b. Examplesofosmoles
table 4. Osmoles
Salt OsmolesNaCl 2KCl 2CaCl2 3
CaCl2=calciumchloride;KCl=potassium chloride;NaCl=sodiumchloride.
3. ConvertingMWtomilliequivalents
table 5. ConvertingMolecularWeighttoMilliequivalents
Convert23.4%NaCl(concentratedNaCl)tomEq/mLMolecularweight(MW)ofNaCl=23+35.5=58.5(addMWofNa+Cl)23.4g × 1equiv × 1000mEq=4mEq/mL100mL58.5g1equiv
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D. CalculatetheOsmolarityofIntravenousFluidsinMilliosmolesperLiter.1. Theosmoticcoefficientcanbeusedtocalculatetheosmolarityofintravenousfluidsbecausesalt
formsdonotcompletelydissociateinsolution.a. WithNaCl,forexample,thereissomeionicattractionbetweenNa+andCl,sotheydonot
completelydissociate,butrather,theyareabout93%dissociatedinsolution(thus,theosmoticcoefficientis0.93).
b. Inclinicalpractice,mostdonotconsidertheosmoticcoefficientwhencalculatingtheosmolarityofNaClorotherelectrolytes,andinreality,theosmoticcoefficientisprobablynotclinicallyrelevant(butisusedinthefollowingexamplesforcompleteness).
2. Normalsaline(NS;0.9%NaCl)
table 6. CalculationforNSmW Osmoles Osmotic Coefficient
58.5g/mol 2 0.930.9g × 1 mol × 2Osm × 1000mOsm × 1000mL×0.93=287mOsm/L100mL58.5g1mol1Osm1L
3. D5W(MW180g/mol)
table 7. Calculation for D5W5g × 1 mol × 1000mOsm × 1000mL=278mOsm/L100mL180g1mol1L
4. OsmolarityofD5W/NS=287mOsm/L+278mOsm/L=565mOsm/L5. OsmolarityofNS+KCl20mEq/L
table 8. CalculationforNSPlusKClStep 1: Convert meq to weight (g)
20mEq×1equiv × 74.5g=1.49gofKCl1000mEq1equiv
Step 2: Calculate mOsm/L
1.49g × 1 mol × 2Osm × 1000mOsm=40mOsm/LL74.5g1mol1Osm
Step 3: Add osmolarity of nS + KCl = 287 mOsm/L + 40 mOsm/L = 327 mOsm/L
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III. HYPeRtOnIC SALIne
A. Concentration:Typicallypreparedas3%(954mOsm/L),7.5%(2393mOsm/L),or23.4%(7462mOsm/L)
B. CommonUsesofHypertonicSaline(HS)1. HSisusedintraumaticbraininjurytoreduceanelevatedICPandtoincreaseBP.
a. TypicallyusedifICPisgreaterthan15mmHgusinganICPmonitorb. IftheserumNaconcentrationisclosetotheupperlimitofnormal(i.e.,145mEq/L),thenitis
preferabletousealowerconcentrationofHS(i.e.,3%).2. HSisusedforsymptomatichyponatremia(symptomsdescribedinhyponatremiasectionbelow).
a. SymptomsgenerallydonotoccurunlessserumNa+is120mEq/Lorless,andtheyincreaseinseverityasNa+decreases.
b. Inanefforttopreventseveresymptomsfromoccurring,somepractitionerstreatasymptomatichyponatremiaiftheserumNa+is120mEq/Lorlessbecauseoftheincreasedriskofsymptomsbelowthislevel.
C. InappropriateUseofHS1. Chronic asymptomatic hyponatremia
a. Asymptomaticsyndromeofinappropriatesecretionofantidiuretichormone(ADH)isusuallytreatedwithfluidrestrictionof1000–1200mLoffluidperday.
b. Hyponatremiaisgenerallyawaterproblem(i.e.,anexcessoffreewater)ratherthanadeficiencyofNa;thus,HSmakeslittlesenseintheabsenceofsymptoms(seeHyponatremiasectionbelow).
2. Hyponatremiaassociatedwithseverehyperglycemia(i.e.,diabeticketoacidosis)a. Typically,serumNawilldecreaseinanon-linearfashioninresponsetohyperglycemia(i.e.,
Na+decreasesbyabout1.6mEq/Lforevery100-mg/dLelevationinglucosebetween100and400mg/dL,butNa+willdecreasebyabout2.4mEq/Lforevery100-mg/dLelevationinglucoseabove400mg/dL).
b. Ashyperglycemiaiscorrectedwithinsulin,theserumNa+willnormalize.3. Hyponatremiaassociatedwithhypervolemia(i.e.,heartfailureleadstotissuehypoperfusion,
whichtriggersthesecretionofADH,causingreabsorptionofwaterfromthekidneysandleadingtohyponatremia)a. Ingeneral,thissituationistreatedwithfluidrestriction.b. Symptomatichyponatremiaisuncommoninpatientswithheartfailure.c. HScouldbeconsideredinsymptomaticpatients;however,theymayneeddiuresistoprevent
worseningvolumeoverload.
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D. PreparationofHS
table 9. CalculationstoPrepareHS
Steps exampleChoosebasesolutions Forthisexample,useconcentratedNaClavailableas23.4%vials
andsterilewatertomake1000mLof7.5%HSSetupalligation 23.4%
7.5%0
Addandsubtract 23.4%7.5parts(from23.4%NaCl) 7.5%0 15.9parts(fromsterilewater) 23.4 parts total
Divide 7.5parts/23.4parts=x/1000mL;x=320.5mLof23.4%NaCl15.9parts/23.4parts=x/1000mL;x=679.5mLofsterilewater
HS=hypertonicsaline;NaCl=sodiumchloride.
E. HSDose1. Doseoptionsfortraumaticbraininjury
a. 3%HS250mLor2–4mL/kgintravenouslyover1–15minutesadministeredforelevatedICPb. 23.4%HS30mLover20–30minutesadministeredforelevatedICP
i. Standingorderssuchas30mLevery4or6hoursareNOTrecommended.ii. IfHSisneededforprolongedreductioninICP,a3%HSconcentrationisgenerally
recommended.2. Dose options for patients with symptomatic hyponatremia
a. TreatmentofpatientswithsymptomatichyponatremiainvolvesasmallbutquickincreaseinserumNa+by0.75–1mEq/L/hourtoaconcentrationof120mEq/L.Then,infusioncanbereducedsothatNa+increasesby0.5mEq/L/hour.
b. Estimateaninfusionrateof3%HSbymultiplyingidealbodyweight(IBW)bydesiredrateofserumNaincreaseperhour.(Note:IBWisusedtoavoidoverdosingobesepatients.)i. Forexample,70kg×1mEq/L/hour=70mL/hourtoincreaseserumNa+by1mEq/Lin1
hour.TheinfusioncanbeadjustedtoachievegoalchangesinserumNa+.ii. Infusionrateof3%HSisgenerally1–2mL/kg/hour.iii. Ingeneral,3%HSisnotrecommendedinasymptomaticpatients;ifusedinanasymptomatic
patient,theadministrationrateshouldgenerallynotexceed0.5–1mL/kg/hour.c. Alternatively,somepractitionersrecommenda250-mLbolusof2%–3%HSover30minutesor
50mLof3%HSadministeredasabolusevery30minutesfortwodoses.
F. AdministrationofHS1. Usecentralintravenousaccessbecausetheosmolarityisgreaterthan900mOsm/L.2. Ifnocentrallineisavailable,canuse2%HS3. Somepractitionersuse3%HSthroughaperipheralintravenousaccesssiteinanemergencybecause
theosmolarityisclosetothecutoffrangeforperipheraladministration.Ifaperipheralsiteisused,monitorforphlebitisandobtaincentralaccessassoonaspossible.
G. ClinicalGoalsandMonitoringforAdministeringHSinPatientswithSymptomaticHyponatremia
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1. Goalsa. Stopsymptoms(describedbelow).b. SafeserumNa+achievedusuallyintherangeof120–125mmol/Ltoavoidadverseneurologic
outcomes.NotethattheimmediategoalforpatientswithsymptomatichyponatremiaisnotanormalserumNa+.
c. ReachedmaximalsafeamountofchangeinserumNa+
i. Maximalsafeamountofchangeisgenerallyregardedas10–12mmol/L(or10–12mEq/L)in24 hours.
ii. Somepractitionerssuggestamaximalchangeof8mmol/Lin24hours.2. MonitorserumNa+every1–4hoursdependingonseverityofsymptoms.
H. ComplicationsofHS1. Centralpontinemyelinolysis(alsoreferredtoasosmoticdemyelinationsyndrome)canoccurwith
rapidcorrectionofhyponatremia.a. Characterizedbypermanentneurologicdamagesuchasparaparesis,quadriparesis,dysarthria,
dysphagia,andcomab. Morelikelytooccurwithrapidcorrectionofchronichyponatremiacomparedwithacute
hyponatremia.ThispartlyexplainswhyitisadvisablenottoadministerHSinpatientswithchronic asymptomatic hyponatremia.
c. PreventbyavoidingchangesinserumNa+ofmorethan10–12mmol/Lin24hoursormorethan18mmol/Lin48hours.
2. HypokalemiacanoccurwithlargevolumesofHS.3. HyperchloremicacidosiscanoccurbecauseoftheadministrationofCl-salts(i.e.,NaCl).Canprevent
byadministeringHSina1:1or2:1ratioofNaClandNa+ acetate4. Hypernatremia5. Phlebitisifadministeredinaperipheralvein6. Heartfailure
a. Fluidoverloadcanoccurbecauseofinitialvolumeexpansion.b. Overtime,HScanhaveadiureticeffect,leadingtointravascularvolumedepletion.
7. Coagulopathycausedbyplateletdysfunction8. HypotensionifHSisadministeredrapidly
I. OtherConsiderationsWhenUsingHS1. Becausehypokalemiacancausehyponatremia,remembertocorrectK+depletionifpresent.AsK+ is
replaced,serumNa+ will increase.2. If150mEqofNa+bicarbonateisaddedto850mLof0.9%NaCl,theresultantsolutionisequivalent
toabout3%HS.Whenaninfusionof150mEqofNa+bicarbonateperliterisindicated,itisrecommendedtoaddNa+bicarbonatetoD5Winsteadof0.9%NaCl.
IV. HYPOtOnIC IntRAVenOuS FLuIdS
A. HypotonicFluidsAdministeredIntravenouslyCanCauseCellHemolysisandPatientDeath.1. Albumin25%dilutedwithsterilewatertomakealbumin5%hasanosmolarityofabout60mOsm/L
andcancausehemolysis.2. “QuarterNS”or0.225%NaClhasanosmolarityof68mOsm/Landcancausehemolysis.
B. AvoidUsingIntravenousFluidwithanOsmolarityLessthan150mOsm/L.
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1. SterilewatershouldNEVERbeadministeredintravenously.2. Someprescribersusehypotonicsalineforapatientwithhypernatremia.
a. Inreality,apatientwithhypernatremiagenerallyneedswater,notNa+.b. Therefore,forpatientswithhypernatremia,enteraladministrationofwaterispreferable.c. Iftheenteralrouteisunavailable,recommendD5Wadministeredintravenously.
C. PreventaPotentiallyFatalErrorbyRecommendingOneoftheFollowingAlternativesinPlaceof0.225%NaCl:1. Recommendchanging0.225%NaCltoD5WaloneoracombinationofD5Wand0.225%NaCl.2. Alternatively,ifthereareconcernsrelatedtohyperglycemiawithusingD5W(50gofdextroseor170
kcal/L),recommendusing2.5%dextroseand0.225%NaCl.3. Alternatively,couldrecommendaddingKCltoincreaseosmolarity4. Recommendadministeringwaterenterally(bymouthorfeedingtube)
V. HYPOnAtRemIA And HYPO-OSmOLAL StAteS
A. SodiumSaltsArethePrimaryDeterminantsofPlasmaOsmolality(andsubsequentfluidshiftsbetweentheICandECcompartments).1. AreductioninserumNa+lessthan136mEq/Lusuallycorrelateswithareductioninplasma
osmolality.2. Hyponatremiawithsubsequenthypo-osmolalitycausesfluidtoshiftintocells(cellular
overhydration).Hypotonichyponatremiacanbedividedintothreetypesonthebasisofvolumestatus:
table 10.ClassificationofHyponatremiaHypervolemic Hyponatremia normovolemic Hyponatremia Hypovolemic Hyponatremia
Description CausedbyexcessNa+andfluidbutfluidexcesspredominates
NormaltotalbodyNa+withexcessfluidvolume(i.e.,dilutional)
DeficitofbothNa+andfluid,buttotalNa+isdecreasedmorethantotalbodywater
Example Heartfailure,cirrhosis, nephroticsyndrome
SIADH Fluidloss(e.g.,emesis,diarrhea,fever),third-spacing,renalloss(diuretics)
Diagnosis UrineNa+<25mEq/Lindicatesedematousdisorders(i.e.,heartfailure,cirrhosis,nephriticsyndrome);UrineNa+>25mEq/Lindicatesacute or chronic renal failure
Urineosmolality>100mOsm/Kg(indicatesimpairedwaterexcretion);urineNa>40mEq/L
UrineNa+<25mEq/LindicatesanonrenallossofNa+(e.g.,emesis,diarrhea);urineNa+>40mEq/LindicatesarenallossofNa+
Treatment Sodiumandwaterrestriction; treatunderlyingcause;vasopressinreceptorantagonists (e.g.,conivaptan,tolvaptan)
Ifdrug-inducedSIADH,removeoffendingagent;fluidrestriction;demeclocycline;vasopressinreceptorantagonists(e.g.,conivaptan,tolvaptan)
Fluidresuscitation(seeabove)
SIADH=syndromeofinappropriatesecretionofantidiuretichormone.
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3. Inselectcases,hyponatremiawillbeassociatedwitheitheranormalorelevatedplasmaosmolality.a. ThisisknownaspseudohyponatremiabecauseNa+contentinthebodyisnotactuallyreduced,
butrather,shiftsfromtheECcompartmentintothecellstomaintainplasmaosmolalityinanormalrange(thus,serumNa+willbelow).i. Severehyperlipidemiacanbeassociatedwithanormalorelevatedplasmaosmolality.ii. Severehyperglycemia(i.e.,duringdiabeticketoacidosis)isassociatedwithanelevated
plasma osmolality.b. Oncetheunderlyingconditioniscorrected,Na+willshiftoutofthecells,andhyponatremiawill
resolve.
B. CausesofHyponatremia1. Replacement of lost solute with water
a. Lossofsolute(e.g.,vomiting,diarrhea)usuallyinvolvesthelossofisotonicfluid;therefore,alone,it will not cause hyponatremia.
b. Afterthelossofisotonicfluid,hyponatremiacandevelopwhenthelostfluidisreplacedwithwater.c. Oneofthemostcommoncausesofhyponatremiainhospitalsisthepostoperativeadministration
ofhypotonicfluid.2. VolumedepletionandorganhypoperfusionstimulateADHsecretiontoincreasewaterreabsorptionin
thecollectingtubules,potentiallycausinghyponatremia.3. SyndromeofinappropriateADHsecretionandcortisoldeficiencyarebothrelatedtoexcessiverelease
ofADH.4. Medications,includingthiazidediureticsandantidepressants(especiallyselectiveserotoninreuptake
inhibitors,butalsotricyclicantidepressants),cancausehyponatremia.Drug-inducedhyponatremiaismorelikelyinelderlypatientsandinthosewhodrinklargevolumesofwater.
5. Renalfailureimpairstheabilitytoexcretediluteurine,predisposingtohyponatremia.
C. SymptomsofHyponatremia
table 11. SymptomsofHyponatremia
Serum Sodium (meq/L) Clinical manifestations120–125 Nausea,malaise115–120 Headache,lethargy,obtundation,unsteadiness,confusion110–115 Delirium,seizure,coma,respiratoryarrest,death
1. Symptomsaregenerallyattributabletohypo-osmolality,withsubsequentwatermovementintobraincellscausingcerebraloverhydration.
2. Ifhyponatremiaoccurschronically,cerebralcellswellingispreventedbyosmoticadaptation.a. Solutesmoveoutofbraincellstopreventtheosmoticshiftofwaterintobraincells.b. Forthisreason,patientswithchronichyponatremiamayshowlesssevereornosymptoms.
3. NeurologicsymptomsarerelatedtotherateofchangeintheserumNa+andtothedegreeofchangeinserumNa+.
4. Acutehyponatremiaoccursover1–3days.
D. TreatmentofHyponatremia1. Treatunderlyingcause.2. RaiseserumNa+atasaferate,definedasachangenogreaterthan10–12mEq/Lin24hours.
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3. Treatmentdependsonvolumestatus,thepresenceandseverityofsymptoms,andtheonsetofhyponatremia(thelattertwohavebeendiscussedpreviously).a. Ifthepatientisnormovolemicoredematous,therearetwotreatmentoptions:
i. Fluidrestrictionisthetypicalfirst-linerecommendation.NotethatNaadministrationisnotrecommendedandthatitcanworsenedema.
ii. Vasopressinantagonists(e.g.,intravenousconivaptan,oraltolvaptan)canbeusedinnormovolemic(i.e.,SIADH[syndromeofinappropriatesecretionofantidiuretichormone])orhypervolemic(i.e.,heartfailure)patientstopromoteaquaresis,increaseserumNa+,alleviatesymptoms,andreduceweight;however,thisapproachiscostlyandhasnotbeenshowntoimproveclinicaloutcomes(i.e.,fallprevention,hospitalization,hospitallengthofstay,mortality)inprospectiverandomizedcontrolledtrials.VasopressinantagonistsaresubstratesandinhibitorsofcytochromeP4503A4isoenzymes;monitorfordruginteractionswithother3A4inhibitorsthatcouldincreaseeffectandleadtoarapidincreaseinserumNa+. Fluidrestrictionincombinationwithavasopressinantagonistduringthefirst24hourscanalsoincreasetheriskofoverlyrapidcorrectionofserumNa+.Ifneeded,fluidrestrictioncanbeusedafter24hours.
b. Ifpatienthasintravascularvolumedepletion,needtoreplacevolumefirstwithintravenouscrystalloids(e.g.,0.9%NaCl)i. Untilintravascularvolumeisrestored,patientwillcontinuetosecreteADH,causingwater
reabsorptionandsubsequenthyponatremia.ii. Onceintravascularvolumeisrestored,ADHsecretionwilldecrease,causingwatertobe
excreted.ThiscanleadtoarapidcorrectionofserumNa+;carefulmonitoringisrequiredtopreventoverlyrapidcorrection.
iii. Volumestatuscanbeassessedbyskinturgor,jugularvenouspressure,andurineNa+.c. Onceintravascularvolumeisrestored,maystillneedtoadministerNa+ to patients who
experiencedvolumedepletion,diuretic-inducedhyponatremia,oradrenalinsufficiencyi. TheamountofNa+(inmilliequivalents)neededtoraisetheserumNa+ to a safe concentration
ofabout120mEq/LisestimatedusingLBWasfollows:0.5(LBW)×(120−Na+)forwomen(multiplyLBWby0.6formen).LBWhasbeenestimatedusingweightinkilogramsandheightincentimetersformalesasLBW=[(0.3)(kg)+(0.3)(cm)−29]orforfemalesasLWB=[(0.3)(kg)+(0.4)(cm)−43];formulapublishedin1966(JClinPathol1966;19:389)
ii. Alternatively,theequationabovecanbemodifiedtoestimatetheNa+deficitinthefollowingmanner:0.5(LBW)×(140−Na+)forwomen(multiplyLBWby0.6formen).IfcalculatingtheNa+deficit,itisrecommendedtoadminister25%–50%ofthedeficitduringthefirst24hourstopreventtheoverlyrapidcorrectionofserumNa+.
iii. RegardlessofthemethodusedtoestimateNa+replacement,theamountofNa+administeredshouldbeguidedbyserialserumNa+ concentrations.
d. PatientswithsymptomatichyponatremiashouldbetreatedwithHS(seesectiononHS).4. Correcthypokalemiaifpresentwithhyponatremia.
a. HypokalemiawillcauseareductioninserumNa+becauseNa+ enters cells to account for the reductioninICK+ to maintain cellular electroneutrality.
b. AdministrationofK+ will correct hyponatremia.c. UsecautionwhengivingK+topreventoverlyrapidcorrectionofserumNa+.
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Patient Cases3. A72-year-oldwomanwithahistoryofhypertensionhasdevelopedhyponatremiaafterstartinghydrochlo-
rothiazide3weeksearlier.Sheexperiencesdizziness,fatigue,andnausea.HerserumNa+is116mEq/L.Herweightis60kg,BPis86/50mmHg,andHRis122beats/minute.Whichoneofthefollowinginitialtreatmentregimensismostrecommended?A. 0.9%NaClinfusedat100mL/hour.B. 0.9%NaCl500-mLbolus.C. 3%NaClinfusedat60mL/hour.D. 23.4%NaCl30-mLbolusasneeded.
4. Forthepatientdescribedabove,whichoneofthefollowingisthebesttreatmentgoalforthefirst24hoursincorrectingherserumNa+fromherinitialvalueof116mEq/L?A. IncreaseNa+concentrationto140mEq/L.B. IncreaseNa+concentrationto132mEq/L.C. IncreaseNa+concentrationto126mEq/L.D. MaintainserumNa+between116mEq/Land120mEq/L.
5. Onedaylater,thepatientfromthequestionabovehasimprovedsomewhat.HerBPisnow122/80mmHg,andherHRis80beats/minute.HerserumNa+is120mEq/L,andK+is3.2mEq/L;shestillfeelstired.Sheiseatingaregulardiet.HerECGisnormal.Whichoneofthefollowingisthebestrecommendation?A. D5W/0.9%NaClplusKCl40mEq/Ltoinfuseat100mL/hour.B. 0.9%NaClinfusedat100mL/hour.C. 3%NaClinfusedat60mL/hour.D. Micro-K20mEqbymouthevery6hours×4doses.
VI. HYPeRnAtRemIA And HYPeROSmOLAL StAteS
A. SerumNa+Greaterthan145mEq/LGenerallyCausesHyperosmolality.1. Theosmoticgradientassociatedwithhypernatremiacauseswatermovementoutofcellsandintothe
ECspace.2. Symptomsareprimarilyrelatedtothedehydrationofbraincells.
B. CausesofHypernatremia1. Lossofwaterbecauseoffever,burns,infection,renalloss,gastrointestinal(GI)loss2. RetentionofNa+becauseoftheadministrationofHSoranyformofNa+
C. PreventionofHypernatremiaThroughOsmoregulation1. Plasmaosmolalityismaintainedbetween275and290mOsm/kgdespitechangesinwaterandNa+intake.2. HypernatremiaispreventedfirstbythereleaseofADH,causingwaterreabsorption.3. Hypernatremiaisalsopreventedbythirst.
a. Hypernatremiaprimarilyoccursinadultswithalteredmentalstatuswhohaveanimpairedthirstresponseordonothaveaccesstoortheabilitytoaskforwater.
b. Hypernatremiacanalsooccurininfants.
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D. CerebralOsmoticAdaptation1. Similartopatientswithhyponatremia,patientswithchronichypernatremiacanhavecerebralosmotic
adaptation.a. Braincellstakeupsolutes,Na+,andK+,thuslimitingtheosmoticgradientbetweentheICandEC
fluidcompartments.b. Thispreventscellulardehydration,anditwillincreasethebrainvolumetowardanormalvalue
despitehypernatremia.2. Becauseofosmoticadaptation,patientswithchronichypernatremiamayberelativelyasymptomatic.
E. SymptomsofHypernatremiaArePrimarilyNeurologic.1. Similartohyponatremia,thesymptomsofhypernatremiaarerelatedtotherateofincreaseinplasma
osmolalityandthedegreeofincreaseinplasmaosmolality.2. Earliersymptomsincludelethargy,weakness,andirritability.3. Symptomscanprogresstotwitching,seizures,coma,anddeathiftheserumNa+isgreaterthan158
mEq/L.4. Cerebraldehydrationcancausecerebralveinrupturewithsubsequentintracerebralorsubarachnoid
hemorrhage.
F. TreatmentofHypernatremia1. Rapidcorrectionofchronichypernatremiacanresultincerebraledema,seizure,permanent
neurologicdamage,anddeath.a. Withosmoticadaptation,thebrainvolumeisraisedtowardnormaldespiteanelevatedserum
osmolarity.b. Osmoticadaptationcombinedwitharapidreductioninplasmaosmolalitycancauseanosmotic
gradient,causingwatertomoveintobraincellswithsubsequentcerebraledema.2. Inpatientswithsymptomatichypernatremia,serumNa+shouldbereducedslowlybynomorethan
0.5mEq/L/houror12mEq/L/day.3. Treathypernatremiabyreplacingwaterdeficitslowlyoverseveraldaystopreventoverlyrapid
correctionofserumNa+.a. UsingLBW,theestimatedwaterdeficit(inliters)=(0.4×LBW)×[(serumNa+/140)−1]in
women(multiplyLBWby0.5inmen).b. Notethatinwomenandmen,thetotalbodywateristypicallyabout50%and60%ofLBW.Thus,
somesourcesrecommendavariationontheaboveequationasfollows:waterdeficit=(0.5×LBW)×[(serumNa+/140)−1]inwomen(multiplyLBWby0.6inmen).However,hypernatremicpatientsaregenerallywaterdepleted;thus,theequationusingthelowervaluesabove(i.e.,40%or0.4and50%or0.5)isreasonable.
4. AdministerfreewaterorallyorintravenouslyasD5W.5. IfconcurrentNa+andwaterdepletion(e.g.,vomiting,diarrhea,diuretic-induceddepletion),canusea
combinationofD5Wand0.25%NaCl6. Ifpatientishypotensivebecauseofvolumedepletion,firstrestoreintravascularvolumewith0.9%
NaCltorestoretissueperfusion.NSisthepreferredcrystalloidforfluidresuscitation,andinthehypernatremicpatient,itisstillrelativelyhypotonic.
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Patient Case6. A74-year-oldwomanhasbeenreceivingJevitytubefeedingsat60mL/hourforthepast8daysthrough
hergastrostomyfeedingtube.Sherecentlysufferedanischemicstroke;sheisresponsive,butshedoesnotcommunicate.HerserumNa+was142mg/dLonthedaytheJevitywasstarted,andithasrisensteadilyto149,156,and163mg/dLondays3,4,and8,respectively,afterthestartofthetubefeedings.Herweightis50kg.Whichoneofthefollowingisthebesttreatmentforherhypernatremia?A. Administersterilewaterintravenouslyat80mL/hour.B. AdministerD5Wintravenouslyat80mL/hour.C. AdministerD5W/0.2%NaClintravenouslyat80mL/hour.D. Administerwaterbyenteralfeedingtube200mLevery6hours.
VII. dISORdeRS OF K+
A. NormalPlasmaK+ConcentrationsAre3.5–5mEq/L.
B. PotassiumIsthePrimaryICCation(maintainselectroneutralitywithNa,theprimaryECcation).
C. PotassiumBalanceIsMaintainedBetweentheICandECCompartmentsbySeveralFactors,Including:1. β2-adrenergicstimulation(causedbyepinephrine)promotescellularuptakeofK
+.2. InsulinpromotescellularuptakeofK+.3. PlasmaK+concentrationdirectlycorrelateswithmovementofK+inandoutofcellsowingtopassive
shiftsbasedontheconcentrationgradientacrossthecellmembrane.(Anormalresponsetodiarrhea-inducedhypokalemiaisforK+toshiftoutofthecellspassively,minimizingthereductioninplasmaK+concentration.)
D. NormalPlasmaConcentrationsofK+AreMaintainedbyRenalExcretion.
E. Hypokalemia(K+concentrationlessthan3.5mEq/L)1. Causesofhypokalemia
a. Reducedintakeseldomcauseshypokalemiabecauserenalexcretionisminimizedbecauseofincreasedrenaltubularabsorption.
b. IncreasedshiftofK+intocellscanoccurwiththefollowing:i. IncreasedpHii. Insulinoracarbohydrateloadiii. β2-receptorstimulationcausedbystress-inducedepinephrinereleaseoradministrationofa
β-agonist(e.g.,albuterol,dobutamine)iv. Hypothermia
c. IncreasedGIlossesofK+canoccurwithvomiting,diarrhea,intestinalfistulaorenteraltubedrainage,andchroniclaxativeabuse.
d. Increasedurinarylossescanoccurwithmineralocorticoidexcess(e.g.,aldosterone)anddiureticuse(e.g.,loopandthiazidetype).
e. HypomagnesemiaiscommonlyassociatedwithhypokalemiacausedbyincreasedrenallossofK+;correctionofplasmaK+requiressimultaneouscorrectionofserummagnesium.
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2. SymptomsofhypokalemiagenerallyoccurwhenplasmaK+isbelow3mEq/Landcanincludethefollowing.a. Muscleweaknessoccursmostcommonlyinthelowerextremitiesbutcanprogresstothetrunk,
upperextremities,andrespiratorymuscles.MuscleweaknessintheGItractcanmanifestasparalyticileus,abdominaldistention,nausea,vomiting,andconstipation.
b. ECGchanges(flattenedTwavesorelevatedUwave)c. Cardiacarrhythmias(bradycardia,heartblock,ventriculartachycardia,ventricularfibrillation)d. Digoxintoxicitycanoccurdespitenormalserumdigoxinconcentrationsinthepresenceof
hypokalemia.e. Rhabdomyolysiscanoccurbecausehypokalemiacancausereducedbloodflowtoskeletalmuscle.
3. Treatmentofhypokalemiaa. Potassiumdeficitcanbeestimatedas200–400mEqofK+forevery1-mEq/Lreductioninplasma
K+(assumingnormaldistributionofK+betweenECandICcompartments).b. AlthoughtheK+deficitcanbeestimated,K+replacementisguidedbyK+concentrations;recheck
every2–4hoursifK+islessthan3mEq/L.c. PotassiumCl-isthepreferredsaltinpatientswithconcurrentmetabolicalkalosisbecausethese
patients typically lose Cl-throughdiureticsorGIloss.Thisisthemostcommonpresentationofhypokalemia.
d. Potassiumacetatecanbeadministeredintravenously,orK+bicarbonatecanbeadministeredorallyforpatientswithametabolicacidosisthatrequiresfrequentK+ supplementation.
e. GuidelinesforadministeringK+
i. PatientswithoutECGchangesorsymptomsofhypokalemiacanbetreatedwithoralsupplementation.
ii. AvoidmixingK+indextrose,whichcancauseinsulinreleasewithasubsequentICshiftofK+.iii. Toavoidirritation,nomorethanabout60mEq/Lshouldbeadministeredthrougha
peripheral vein.iv. Recommendedinfusionrateis10–20mEq/hourtoamaximumof40mEq/hour(thefaster
rateshouldbeinfusedthroughacentralvenouscatheter).v. PatientswhoreceiveK+atratesfasterthan10–20mEq/hourshouldbemonitoredusinga
continuousECG.
table 12.K+ Replacement
Plasma K+ (meq/L)
treatmenta Comments
3–3.5 OralKCl60–80mEq/dayifnosignsorsymptoms (dosesgreaterthan60mEqshouldbedividedto avoidGIadverseeffects)
RecheckK+daily
2.5–3 OralKCl120mEq/dayorIV60–80mEqadministeredat10–20mEq/hourifsignsorsymptoms
MonitorK+ closely (i.e.,2hoursafterinfusion)
2–2.5 IVKCl10–20mEq/hour ConsidercontinuousECGmonitoringLessthan2 IVKCl20–40mEq/hour RequirescontinuousECGmonitoring
aTreatmentdosesareforpatientswithnormalkidneyfunctionandshouldbereducedforpatientswithkidneydysfunctionorelderlypatients.ECG=electrocardiogram;GI=gastrointestinal;IV=intravenous;KCl=potassiumchloride;K+=potassium.
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F. Hyperkalemia1. Causesofhyperkalemia
a. Increasedintakeb. ShiftofK+fromtheICtotheECcompartmentcauseshyperkalemiaandcanoccurwiththe
following:i. Acidosisii. Insulindeficiencyiii. β-Adrenergicblockadeiv. Digoxinoverdosev. Rewarmingafterhypothermia(e.g.,aftercardiacsurgery)vi. Succinylcholine
c. Reducedurinaryexcretioncanoccurwithi. Kidneydysfunctionii. Intravascularvolumedepletioniii. Hypoaldosteronismiv. Potassium-sparingdiureticsv. Angiotensin-convertingenzymeinhibitorsandangiotensinreceptorblockers
2. Symptomsofhyperkalemiaa. Muscleweaknessorparalysisiscausedbychangesinneuromuscularconductionandtypically
occurswhenplasmaK+exceeds8mEq/L.b. Abnormalcardiacconductioncanfirstmanifestaspeaked,narrowedTwaves(typically,when
plasmaK+exceeds6mEq/L),wideningoftheQRS,andcanprogresstoventricularfibrillationandasystole.
c. NotallpatientswillexperienceECGchanges,andtheinitialmanifestationofhyperkalemiacanbeventricularfibrillation;thus,consideremergencytreatmenteveninpatientswithnoECGchangesifplasmaK+exceeds6.5mEq/L.
d. Conductiondisturbancesareenhancedbyhypocalcemia,hyponatremia,acidosis,andrapidelevationintheplasmaK+ concentration.
3. Pseudohyperkalemiashouldbesuspectedifthereisnoapparentcauseorsymptomsofhyperkalemia.a. CanoccurifK+isreleasedfromcellswhile–orafter–obtainingthebloodspecimen;usually
becauseoftraumaduringvenipunctureb. CanoccurfrommeasurementoftheserumratherthantheplasmaK+concentration;causedbyK+
releaseduringcoagulation4. Treatmentofhyperkalemia
a. PatientswithanasymptomaticelevationintheplasmaK+whodonothavesignsorsymptomscanbetreatedwithacationexchangeresin(e.g.,Napolystyrenesulfonate)alone.
b. Urgentandimmediatetreatmentisrequiredforpatientswiththefollowingsignsorsymptoms:i. PlasmaK+above6.5mEq/Lii. Severemuscleweaknessiii. ECGchanges
c. Calciumshouldbeadministeredintravenouslytopatientswithsymptomatichyperkalemiatopreventhyperkalemia-inducedarrhythmiasevenifpatientsarenormocalcemic.i. Calciumgluconatecanbeadministeredperipherallyandispreferredovercalciumchloride
(CaCl)becauseofareducedriskoftissuenecrosis;doseis10mL(equivalentto1g,90mgelemental,or4.65mEq)of10%Ca++gluconateadministeredover2–10minutes;mayrepeatin5minutesifnoimprovementinECG.Calciumchloridecanbeusedifcentralintravenousaccessisavailable;however,thedoseshouldbeadjustedbecause10mL(1g,270mgelemental,or13.6mEq)provides3timestheamountofelementalCaascalciumgluconate.
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ii. Onsetiswithinminutes,butdurationisshort(30–60minutes).iii. WillnotreduceplasmaK+,butwillantagonizetheeffectofK+incardiacconductioncellsiv. Useinurgentcircumstanceswhilewaitingforothermeasures(e.g.,insulinandglucose)to
lowerplasmaK+.v. Avoiduseinpatientsreceivingdigoxinbecausehypercalcemiacanprecipitatedigoxin
toxicity,andtherearereportsofsuddendeath.d. Thefollowingtreatmentoptionsaretransient,causingatemporaryshiftofK+fromtheECfluid
intothecells,andshouldbeusedforsymptomatichyperkalemia.i. Insulinandglucose
(a) Doseisregularinsulin10unitsintravenouslyplus25–50gofglucoseadministeredasa50%dextroseintravenouspushtopreventhypoglycemia.
(b) TypicallylowersplasmaK+by0.5–1.5mEq/Lwithin1hourandmaylastforseveralhours(c) Ifpatientsarehyperglycemic,insulinalonecanbeadministered.(d) Morepredictableinpatientswithkidneyfailurethansodiumbicarbonateorβ2-adrenergic
agonists(e) Cautionwithincreasedriskofinsulinerrorswhenusedinemergencysituations(e.g.,
nursespreparinginsulininfusions).Errorsinvolvingcalculations(100units/mL)anduseof4-or10-mLsyringesinsteadofaninsulinsyringearecommon.
ii. Sodiumbicarbonate(a) Doseis50mEqofsodiumbicarbonateinfusedslowlyover5minutes;mayrepeatin30
minutesifneeded(b) MaylowerplasmaK+within30–60minutesandpersistforseveralhours(c) Theefficacyofbicarbonateisdisputed,anditseemsleasteffectiveinpatientswith
advancedkidneydisease;maybeeffectiveinpatientswithunderlyingmetabolicacidosisiii. β2-adrenergicagonists(e.g.,albuterol)
(a) Doseisalbuterol10–20mgnebulizedover10minutesor0.5mgintravenously(notavailableintheUnitedStates).
(b) WilllowerplasmaK+by0.5–1.5mEq/L(c) Onsetiswithin90minuteswithinhalation.(d) Avoiduseinpatientswithcoronaryischemiabecauseofriskoftachycardia.(e) Upto40%ofpatientswillnotrespondtoinhaledalbuterol;therefore,itisnot
recommendedasasingleagentforurgenttreatmentofhyperkalemia;consideruseincombinationwithinsulin.
e. ThetreatmentoptionsaboveshouldbefollowedbyoneofthefollowingagentstoremoveexcessK+fromthebody.i. Diuretics
(a) Looporthiazide-typediureticsincreaseK+renalexcretion.(b) Ineffectiveinpatientswithadvancedkidneydisease
ii. Cation-exchangeresin(a) ExchangesNa++forK+,resultinginGIexcretionofK+
(b) Becauseofaslowonset(2hours)andunpredictableefficacy,Na++ polystyrene sulfonate (Kayexalate)isnotindicatedforemergencytreatmentofhyperkalemia.
(c) Oraldoseofsodiumpolystyrenesulfonateis15grepeatedevery6hoursasneeded.Thiscanbemixedin20–100mLofwaterorsyrup,butitisnolongerrecommendedtomixin70%sorbitolbecauseoftheriskofintestinalnecrosis(therearereportsaswellwiththepremixed33%sorbitolsuspension,but70%sorbitolappearstohaveastrongercorrelationwithintestinalnecrosis).Oralsorbitolcanpreventconstipationassociatedwiththeresin;however,thehighestriskofintestinalnecrosisoccurswhenadministeredtopatientswithin1weekofsurgery(occursinabout1.8%ofpatients).
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(d) Althoughtheoralrouteismoreeffective,canalsogive30–50gasaretentionenemamixedin100–200mLofanaqueousvehicle(e.g.,water,10%dextrose)thathasbeenwarmedtobodytemperatureandkeptincolonfor30–60minutesorupto3hours.Irrigatecolonafterenema.(1) Sorbitolisnotrecommendedasavehicleforrectalusebecauseoftheriskof
intestinalnecrosisandotherseriousGIadverseevents.PatientswithkidneydiseaseareatincreasedriskoftheseGIadverseeffects.
(2) CautioninpatientswithkidneyfailureorheartfailurecausedbyNaretentioniii. Dialysis
(a) Usedwhenothermeasuresareineffectiveorwhenseverehyperkalemiaispresent(b) PlasmaK+fallsbymorethan1mmol/Linthefirsthourofdialysisandbyabout2
mmol/Lafter3hoursofdialysis.(c) HemodialysisremovesK+fasterthanperitonealdialysis.(d) MonitorforreboundincreaseinK+afterdialysis.(e) Usedinpatientswithadvancedkidneydisease
Patient Case7. A61-year-oldman isbrought to theemergencydepartmentwithshortnessofbreathandbilateral lower
legedema.PertinentvitalsignsandlaboratoryvaluesincludeHR30beats/minute,BP102/57mmHg,K+ 7.9mEq/L,Na+139mEq/L,glucose228mg/dL,Ca++8.8mg/dL,digoxin2.0ng/mL,BUN49,andCr2.4mg/dL.HisECGshowswideQRSandpeakedTwaves.Hismedicalhistoryincludesheartfailure,atrialfibrillation,coronaryarterydisease,peripheralarterialdisease,anddiabetes.Thepatienthasperipheralintravenousaccessandanexternalpacemaker.Whichoneofthefollowingismostappropriate?A. Calciumgluconate10mLintravenouslyover2minutes.B. Insulin10unitsintravenously.C. Sodiumbicarbonate50mEqintravenouslyover10minutes.D. Albuterol10mgnebulizedover10minutes.
VIII. dISORdeRS OF mAgneSIum HOmeOStASIS
A. NormalSerumMagnesiumConcentrationIs1.7–2.3mg/dL(1.4–1.8mEq/Lor0.85–1.15mmol/L).
B. Hypomagnesemia(serummagnesiumconcentrationlessthan1.7mg/dL)1. Usuallyassociatedwithimpairedintestinalabsorption(e.g.,ulcerativecolitis,diarrhea,pancreatitis,
chroniclaxativeabuse),inadequateintake,hypokalemia,orincreasedrenalexcretion(e.g.,diureticuse)a. Commoninhospitalizedpatientsb. Usuallyassociatedwithalcoholismanddeliriumtremens
2. Oftenoccursconcurrentlywithhypokalemiaandhypocalcemia3. Signsandsymptoms
a. Neuromuscularsymptomsincludetetany,twitching,andseizures.b. Cardiovascularsymptomsincludearrhythmias,suddencardiacdeath,andhypertension.
4. Treatmenta. Oralsupplements(e.g.,magnesiumoxide,magnesium-containingantacidsorlaxatives)canbe
usedforasymptomaticpatients;however,treatmentislimitedbythehighfrequencyofdiarrhea.
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b. Symptomaticpatientsshouldinitiallybetreatedwith1–4g(8–32mEq)ofmagnesiumsulfatebyslowintravenousinfusion(about1g/hourtoavoidhypotensionand/orincreasedrenalexcretionbecauseofrapidadministration),followedbyabout0.5mEq/kg/dayaddedtointravenousfluidandadministeredasacontinuousinfusion.Foremergencytreatment(e.g.,torsades),magnesiumcanbeadministeredbyintravenouspush.
c. Reducedosebyhalfinpatientswithkidneyinsufficiency.d. Aroundhalfofadministeredmagnesiumisexcretedintheurine;therefore,magnesium
replacementshouldoccurover3–5days.
C. Hypermagnesemia(serummagnesiumgreaterthan2.3mg/dL)1. Rarelyoccursandisgenerallyassociatedwithchronickidneydisease2. Signsandsymptomsincludenausea,vomiting,bradycardia,hypotension,heartblock,asystole,
respiratoryfailure,anddeath;signsandsymptomsrarelyoccurunlessmagnesiumconcentrationisgreaterthan4–5mg/dL.
3. Treatmenta. Discontinueallmagnesium-containingmedications.b. Asymptomaticpatientswithnormalkidneyfunctioncanbetreatedwith0.9%NaClandloop
diuretics.c. Symptomaticpatientsshouldbetreatedwith100–200mgofelementalCaadministered
intravenouslyover5–10minutesforcardiacstability.d. Hemodialysismaybeneededforpatientswithkidneydisease.
IX. dISORdeRS OF PHOSPHORuS HOmeOStASIS
A. NormalSerumPhosphorusConcentrationIs2.5–4.5mg/dL.
B. Hypophosphatemia(serumphosphorusconcentrationlessthan2.5mg/dL)1. Causes of hypophosphatemia
a. Increasedrenalelimination(e.g.,diuretics,glucocorticoids,sodiumbicarbonate)b. Rapidlyrefeedingpatientswithchronicmalnutrition(seerefeedingsyndromeinNutritionsection)c. Respiratoryalkalosisd. Treatmentofdiabeticketoacidosis;phosphorusshiftsintotheICcompartmentasdiabetic
ketoacidosisiscorrected2. Signsandsymptoms
a. Tissuehypoxiacanoccurbecauseofadecreaseinoxygenreleasetoperipheraltissues.b. Neurologicmanifestationsincludeconfusion,delirium,seizures,andcoma.c. Pulmonaryandcardiacsymptomscanincluderespiratoryfailure,difficultyweaningfrom
mechanicalventilation,heartfailure,andarrhythmias.d. Otherorgansystemsaffectedincludemuscle,hematologic,bone,andkidney.
3. Preventionandtreatmenta. Preventhypophosphatemiabysupplementingintravenousfluidwith10–30mmol/Lintravenous
phosphorusinpatientsatriskofhypophosphatemia(e.g.,malnourished,alcoholism,diabeticketoacidosis).
b. Oralphosphorusproducts(e.g.,K-PhosNeutral;alsocontainK+andNa)canbeusedforasymptomaticpatients,buttheyarepoorlyabsorbed.
c. Symptomaticpatientsshouldreceive15–30mmol(or0.5–0.75mmol/kgofIBW)ofphosphorus(Na+phosphateorK+phosphate)administeredintravenouslyover3–6hours(maximalrateis7.5mmol/hour).Note:Na+content(4mEqper3mmolphosphate)andK+content(4.4mEqper3mmolphosphate)
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C. Hyperphosphatemia1. Typicallyoccursinpatientswithchronickidneydiseaseorhypoparathyroidism2. Ingeneral,patientsareasymptomatic,buttheycanhavesignsandsymptomsincludinghypocalcemia,
ECGchanges,paresthesias,andvascularcalcifications.3. Treatment(seetreatmentofhyperphosphatemiaintheNephrologychapter)
X. dISORdeRS OF CALCIum HOmeOStASIS
A. NormalSerumCa++ConcentrationIs8.5–10.5mg/dL(totalCa++includesboundandunboundCa++),andNormalIonizedCa++Is1.1–1.3mmol/L.
B. DistributionofCa1. ECfluidcontainslessthan1%ofthetotalbodystoresofCa++;99%oftotalbodystoresofCa++
isinskeletalbone.a. AbouthalfofCa++intheECcompartmentisboundtoplasmaproteins(primarilyalbumin).b. TheactiveformofCa++istheunboundorionizedCa++.
2. IonizedCa++isregulatedbyparathyroidhormone,phosphorus,vitaminD,andcalcitonin.
C. Hypocalcemia1. Occursinpatientswithchronickidneydisease,hypoparathyroidism,vitaminDdeficiency,
alcoholism,andhyperphosphatemia,aswellasinpatientsreceivinglargeamountsofbloodproductsorpatientsundergoingcontinuousrenalreplacementtherapy(CRRT[i.e.,Ca++ chelates with citrate in bloodproductsorCRRT])
2. FactorsthatcauseanincreaseinECCa++bindingtoalbumin(e.g.,metabolicalkalosis)cancauseareductioninplasma-ionizedCa++concentration,leadingtosymptomatichypocalcemia.
3. AlowserumalbuminwillcauseafalselylowtotalserumCa,soanadjustmentisnecessary.Forevery1-g/dLdecreaseinserumalbuminlessthan4g/dL,add0.8mg/dLtototalserumCaconcentration to correct the value.
4. Signsandsymptomsincludetetany,musclespasms,hypoactivereflexes,anxiety,hallucinations,lethargy,hypotension,andseizures.
5. Treatmenta. Asymptomatichypocalcemiaassociatedwithhypoalbuminemiaistypicallyassociatedwith
normalionizedCa++concentrationsandthereforedoesnotrequiretreatment.b. AsymptomatichypocalcemiacanbetreatedwithoralCa++supplementsatadoseof2–4g/dayof
elemental Ca++;patientsmayalsorequirevitaminDsupplementation.c. Symptomatichypocalcemiaistreatedwith200–300mgofelementalCa++administered
intravenouslyover5–10minutes,followedbyacontinuousinfusion.i. Equivalentto1gofCaCl2(273mgofelementalCa
++)administeredthroughacentralintravenouscatheter;peripheraladministrationofCaCl2canresultinseverelimbischemia
ii. Equivalentto2–3gofCa++gluconate(180–270mgofelementalCa++);preferredforperipheralintravenousadministration
iii. Do not infuse Ca++ataratefasterthan60mgofelementalCa++perminute;rapidadministration,whichisnotrecommended,isassociatedwithhypotension,bradycardia,orasystole.
iv. ThedurationofabolusdoseofCa++isideally1–2hours,followedbyacontinuousinfusionrateof0.5–2mg/kg/hourofelementalCa++.
D. Hypercalcemia(serumCa++concentrationgreaterthan10.5mg/dL)isusuallyrelatedtomalignancyorhyperparathyroidism;seeOncologySupportiveCarechapter.
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XI. enteRAL nutRItIOn
A. Indication:Enteralnutritionisusedinhemodynamicallystablepatientsatriskofmalnutritioninwhomitisanticipatedthatoralfeedingswillbeinadequateforatleast1–2weeks.Malnutritionisassociatedwithpoorwoundhealingandincreasedriskofinfection.AccordingtotheAmericanSocietyforParenteralandEnteralNutrition(ASPEN)guidelines,well-nourishedadultswithoutexcessivemetabolicstresscanusuallytoleratelittletononutritionforupto7days.
B. ENContraindications1. Completeintestinalobstruction2. GIfistula(ifafeedingtubecannotbeplacedawayfromthefistulaorifhigh-outputfistula,whichis
definedasgreaterthan500mL/dayofoutput)3. Extremeshortbowel4. Severediarrheaorvomiting5. Hemodynamicinstabilityorintestinalischemia6. Paralyticileus(however,manypatientscanbefedthroughthesmallbowel,despiteanileus)7. Note:TheabsenceofbowelsoundsisNOTacontraindicationfortheprovisionofEN
(i.e.,positivebowelsoundsarenotrequiredforENinitiation).ENpromotesgutmotility.
C. ENAdministrationRoutes1. Orogastrictubesarepreferredinpatientswithnasal/facialtraumaorsinusitis,buttheyare
uncomfortableforalertpatients.2. NGtubesarethemostcommontubesforshort-termenteralaccess,andtheycanbeusedforstomach
decompressioninadditiontofeeding.a. Prolongedusecancausesinusitisornasalmucosalulceration.b. PatientswithagastricileuswillnottolerateNGfeedingsandwillhaveanincreasedriskof
aspiration.3. NasoduodenaltubesaresmallerandmoreflexiblethanNGtubes.
a. Ideally,thetipisplacedpastthepyloricsphinctertoimprovetubefeedingtoleranceandpreventaspiration.
b. Thesetubes,whicharesmallerthanNGtubes,willclogifnotflushedappropriately.c. Patientswithagastricileusmaytoleratethistypeoffeedingtube.
4. NasojejunaltubesareadvancedintothefourthportionoftheduodenumorpasttheligamentofTreitz.5. Gastrostomytubes(alsoknownasPEGtubesforpercutaneousendoscopicgastrostomy)areplaced
throughtheabdominalwallintothestomachforpatientsrequiringlong-termfeeding.6. Jejunostomytubesareplacedthroughtheabdominalwallintothejejunumusuallytofacilitate
immediatepostoperativeorpostinjuryfeeding.
D. ENDelivery1. Gravitycontrolreferstodeliverywithtubingthatisfittedwitharollerclamptoallowinfusioninto
thestomachasdesired.2. Continuousinfusionusinganenteralfeedingpumpismostcommonlyusedinhospitalsbecauseof
thereducedriskofaspirationcomparedwithbolusfeedings;mustbeusedforduodenalorjejunalfeedings
3. Cyclicfeedingsareadministeredcontinuouslyfor10–12hours(overnight)tofacilitatepatientmobilityduringthedaytime.
4. Intermittentbolusfeedingof100–300mLfor30–60minutesevery4–6hourscanonlybeusedforfeedingtubesendinginthestomach.
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E. BenefitofEN1. ENispreferredinpatientswithafunctionalGItractbecauseitisassociatedwithalowerriskofinfection
thanPN.EarlyadministrationofENisassociatedwithdecreasedinfectionandshorterlengthofstay.2. GImucosalatrophyoccurswithanabsenceofEN.Thiscanleadtoanincreasedriskofbacterial
translocationbecausegutbacteriacancrosstheweakenedintestinalbarrier.
F. ENFormulations1. Typicallycontaincarbohydrate,fat,protein,electrolytes,water,vitamins,andtraceelementsinvarying
amounts2. Intactorpolymericformulasareusedinpatientswithnormaldigestiveprocesses,andtheytypically
contain1–1.2kcal/mL.ExamplesincludeOsmoliteandIsocal.a. Thesearegenerallyinexpensiveandanappropriatefirstchoiceformanypatients.b. Somepolymericformulasareconcentratedforpatientsrequiringfluidrestrictionandcontain2
kcal/mL.ExamplesincludeMagnacal,TwoCalHN,andDeliver2.0.c. Somepolymericformulasaredesignedfororaladministrationandareusedtosupplementthe
patient’sdiet.ExamplesincludeBoostandEnsure.3. Elementalformulasareeasilydigestedforpatientswithimpaireddigestivecapacityormalabsorption
(e.g.,shortbowel,pancreaticinsufficiency);theyaretypicallymoreexpensivethanpolymericEN.ExamplesincludeOptimental,Peptamen,VitalHN,andVivonexTEN.
4. SomeENcontainsfiberforpatientswithconstipation.ExamplesincludeUltracalandJevity.5. Disease-specificEN
a. ENforpatientswithrenalfailureistypicallyconcentrated(i.e.,2kcal/mLtoadheretofluidrestrictions)andcancontainreducedamountsofproteinandelectrolytes(fornondialysispatients)ormoreproteinandmoderateelectrolytes(fordialysispatients).ExamplesincludeMagnacalRenalandNepro.
b. SomeENproductsdesignedforpatientswithrespiratoryfailurehavemorecaloriesfromfat(40%–55%oftotalcalories)andfewerfromdextrosetoreducetheproductionofCO2(dextroseismetabolizedtowaterandCO2)andfacilitateventilatorweaning.However,excessiveCO2
productionisprimarilycausedbyoverfeedingwithtotalcaloriesratherthanthetotalamountofdextrose;therefore,thesemoreexpensiveformulationsmaynotbenecessaryaslongasthepatientisnotbeingoverfed;examplesincludePulmocare,Respalor,andNutriVent.
c. ENforpatientswithdiabeteshasmorecaloriesfromfat,fewercaloriesfromcarbohydrates,andaddedfibertoimproveglycemiccontrol.ExamplesincludeChoiceDMandGlucerna.
d. ENforpatientswithhepaticfailureandhepaticencephalopathycontainsmorebranched-chainAAandlessaromaticAA,whichmayimproveencephalopathy(controversial).NutriHepisanexample.
e. ENforhighlystressedpatients(e.g.,trauma,burninjury,acuterespiratorydistresssyndrome,sepsis)isenhancedwithprotein,arginine,glutamine,omega-3fattyacids,nucleotides,orbetacarotene.Theseenteralformulationsaredesignedtoenhanceimmunefunctionandclinicaloutcomes.ExamplesincludeImpactGlutamineandOxepa.
G. ENComplications1. Impropertubeplacementordisplacement2. Cloggedfeedingtubes
a. Preventbyflushingfeedingtubebefore,between,andaftertheadministrationofeachdrug.b. Unclogfeedingtubeswithwarmwater,cola,pancreaticenzymes,orNabicarbonate.
3. Aspiration pneumoniaa. Preventbykeepingtheheadofbedelevatedat30–45degrees.b. Preventbymonitoringgastricresidualsanddiscontinuinginfusionifgastricresidualvolumeis
greaterthan250–500mL.
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i. PreventdelaysingastricemptyingusinganENformulawithlessfat.ii. Gastricmotilitycanbeincreasedwithmetoclopramide(5–20mgintravenouslyevery6hours)
and/orerythromycin(250mgintravenouslyevery6–8hoursadministereduntiltoleratingENforatleast24hours);cancombinemetoclopramideanderythromycin,butmonitorfordiarrheaandtachyphylaxis
c. AdministeringENpastthepyloricvalveusingaduodenalfeedingtubecanpreventaspirationpneumonia.
d. PreventalsobyinitiatingENataslowrate(e.g.,20mL/hour)andadvanceevery4–6hoursastoleratedtogoalrate.
4. Diarrheaa. Morecommonwithelementalproductsbecauseofahigherosmolarityb. Considerothercausesofdiarrheasuchasantibioticuse,infection,lactoseintolerance,magnesium,
andsorbitolinliquidpreparations.5. Constipationcanbepreventedbyaddingfiberormetoclopramide.6. Dehydration7. HypernatremiaoccurswhenpatientsaregiveninsufficientwaterwhilereceivingEN.
a. Patientsrequireabout1mLofwaterforeachcalorie.b. Hypernatremiatypicallyoccursinpatientswithalteredmentalstatus.c. Calorie-dense(i.e.,1.5or2kcal/mL)ENformulashavelesswaterthanproductscontaining1
kcal/mLandthereforerequireadditionalwatertopreventhypernatremia.8. Nasopharyngealerosions,epistaxis,tracheoesophagealfistula9. Sinusitis10. Electrolyteabnormalitiesaremostlikelytooccurinpatientswhodeveloprefeedingsyndrome
(discussedlater).
Patient Case8. A72-year-oldfemalepatientweighing65kgisreceivingMagnacalRenal,acalorie-richtubefeedingde-
signedforpatientswithkidneydisease.Thepatient’sbaselineandcurrentCris1.5mg/dL,andherurineoutputisabout50mL/hour.Thetubefeedingisinfusingatagoalrateof35mL/hourthroughanNGfeed-ingtubeproviding2kcal/mL,35mEq/LofNa+,and710mL/Lofwater.Thepatient’sserumNa+ was 140 mEq/Lwhenthetubefeedingwasinitiatedafewdaysago,andnow,herNa+is145mEq/L.Whichoneofthefollowingrecommendationsisthebestapproachforpreventinghypernatremiainthispatient?A. ChangetoanENformulawithalowerconcentrationofNa+.B. AdministerintravenousD5Wat45mL/hour.C. Administer200mLofwaterthroughafeedingtubeevery4hours.D. Reducethetubefeedingto30mL/hour.
H. ENMonitoring1. Bloodglucoseconcentration2. Headofbedelevationto30–45degrees3. Gastricresidualsarechecked,andinfusionrateisgenerallyheldorreducediftheresidualamount
exceeds250–500mL(appliestogastrictubefeedingsonly,notsmallbowel).AccordingtotheSocietyofCriticalCareMedicineandASPENguidelines,holdingENforgastricresidualvolumeslessthan500mLintheabsenceofothersignsofintoleranceshouldbeavoided.
4. GItolerance
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a. Abdominalpainand/ordistensionb. Stoolfrequencyandvolumec. Gastricresidualsd. Nausea/vomiting/diarrhea
5. Prealbuminweekly.(Exception:Notrecommendedincriticallyillpatientsbecauseitreflectsacute-phaseresponseratherthannutritionalstatus)
6. SerumNaandotherelectrolytes7. Woundhealingisasignofadequatenutritionaltherapy.
I. DevelopinganENRegimen
table 13. DevelopinganENRegimen
Steps Calculation guide exampleDeterminecaloricrequirements 25–30kcal/kg/dayORestimate
energyrequirementsusinganequationsuchastheHarris- Benedictequation(seemoredetailsinParenteralNutritionsectionandCriticalCarechapter)
A60-kgpatientwouldrequireabout25kcal/kg/day×60kg=1500kcal
Chooseaformulaandassessthecalories per milliliter
Usually1,1.2,1.5,or2kcal/mL Ultracalprovides1kcal/mL
Determine infusion rate (VolumeofEN)/24hours 1500mL/24hours=62.5mL/hourMakesurepatientwillreceive enoughprotein
Seeproductinformationtofindproteincontent(seeproteinrequirementsinParenteral Nutritionsection)
Ultracalprovides45g/Lofprotein;therefore,1500mLwillprovide67.5gofproteinor1.1g/kgforapatientweighing60kg
Makesurepatientwillreceiveabout 1mLofwaterforeachcalorie
Seeproductinformationtofind water content
Ultracalprovides830mL/Lofwater.Apatientreceiving1500mL/daywouldneedabout250mLofadditionalwater.Thiscanbeadministeredaswaterflushesthroughthefeedingtube(i.e.,60–70mLevery6hours)
EN=enteralnutrition.
J. DrugAdministrationUsingEnteralAccess1. Liquidsarepreferable,andtheyshouldbedilutedwith2–3timesthemedicationvolume,withsterile
waterforirrigation.2. Diarrheacanoccurwithmedicationshavingahighosmolality(e.g.,medicationsmixedinsorbitol).3. Flushwith20mLofwaterbeforeandafterdrugadministration.4. Donotcrushsustained-releaseorenteric-coatedpills.5. Mixcrushedtabletsorcapsulecontentswith10–15mLofsterilewaterforinjection,andadminister
eachdrugseparately.6. Mayneedtodiscontinuetubefeedingsbeforeandafterdrugadministrationtemporarilytoprevent
reducedbioavailability(e.g.,fluoroquinolones,phenytoin,warfarin,bisphosphonates)7. Considerfeedingtubelocationandsubsequentdrugabsorption(e.g.,forefficacy;antacidsneedtobe
administeredintothestomach,nottheduodenum).
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XII. PARenteRAL nutRItIOn
A. PNistheadministrationofintravenousnutritioninpatientswithanonfunctioningorinaccessibleGItractinwhichthedurationofPNisanticipatedtobeatleast7days(i.e.,itisanticipatedthatthepatientwillbeunabletobefedorallyorenterallyforatleast7days).
B. IndicationsforPN1. Severepancreatitis2. Peritonitis3. Severeinflammatoryboweldisease(e.g.,Crohndisease,ulcerativecolitis)4. Extensivebowelresection(e.g.,shortbowelsyndrome)causingmalabsorptionormaldigestion5. Completebowelobstruction6. Severeintractablevomitingordiarrhea7. Inabilitytomeetfullnutritionalneedsbyenteralroutealone(canusePNassupplementtoEN)
C. IntravenousInfusionofPN1. PNisusuallyadministeredthroughacentralline.Thisincludesanyintravenouscatheter(e.g.,
peripherallyinsertedcentralcatheterorPICC,Hickman,Port-a-Cath)wherethetipofthecatheterisinthesuperiorvenacavaoradjacenttotherightatrium(femoralcathetersshouldbeavoidedbecauseofhigherriskofvenousthrombosisandcatheter-relatedinfection).
2. Peripheralaccessisdefinedasthecathetertippositionoutsidethecentralvesselsorinferiororsuperiorvenacava;ifaperipheralveinisusedforPNadministration,theosmolaritymustnotexceed900mOsm/L.PeripheraladministrationcanbeusedinpatientswithanappropriateindicationforPN(seeabove)inwhomcentralintravenousaccessisunavailableandtheneedforPNisexpectedtobelessthan2weeks.a. Finaldextroseconcentrationshouldbe10%orless.b. FinalAAconcentrationshouldbe2.5%–4%.c. Caconcentrationshouldbe5mEq/Lorless.d. Potassiumconcentrationshouldbe40mEq/Lorless.
3. Inhospitalizedpatients,PNistypicallyadministeredasacontinuousinfusion,whichshouldbecompletedwithin24hours.
4. AmbulatorypatientsmaypreferacyclicPNinwhichthePNisusuallyinfusedfor12hoursovernight.
5. Infusionsaregenerallybettertoleratedbypatientsiftheyareremovedfromtherefrigerator30–60minutesbeforeinfusion.
table 14. EstimatingtheOsmolarityofPN
nutrient estimated OsmolarityAminoacids 10mOsm/LDextrose 5mOsm/LLipidemulsion20% 1.3–1.5mOsm/LSodium 2mOsm/mEqPotassium 2mOsm/mEqCalciumgluconate 1.4mOsm/mEqMagnesiumsulfate 1mOsm/mEq
PN=parenteralnutrition.
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D. TypesofPNAdmixtures1. 2-in-1referstoPNinwhichallnutrientsaremixedinthesameintravenousbag,exceptforlipids.
a. Lipidsareinfusedseparatelyatnofasterthan0.1g/kg/hour.b. Rapidadministrationoflipidsisassociatedwithheadache,fever,nausea,hypertriglyceridemia,
dyspnea,cyanosis,flushing,sweating,andbackorchestpain.c. Lipidinfusiontimeshouldbelessthan12hoursbecauseofthepotentialformicrobialgrowth
afterthistime(growthisreducedwhenlipidsaremixedwithdextroseandAA,asinthe3-in-1below,becauseofreducedpHandincreasedosmolarity).
d. Administrationtubingfora2-in-1shouldbechangedevery72hours;lipidtubingshouldbediscardedafteruse(nolongerthan12hours).
2. 3-in-1referstoPNinwhichallnutrientsaremixedinthesameintravenousbagtoformalipidemulsion.a. Stabilityofa3-in-1dependsonthepH,whichisprimarilydeterminedbythefinalconcentration
ofAA(maintainbetween2.5%and4%).b. Donotaddconcentrateddextrosedirectlytoalipidemulsionwhenmixing(seeorderofmixing
below).c. AvoidexcessiveamountsofCaandmagnesium(seerecommendeddosesbelow).d. Administrationtubingfora3-in-1shouldbechangedevery24hours.
table 15.2-in-1PNComparedwith3-in-1PN
Advantages disadvantages
2-in-1 Longerstability(1–2months)VisualinspectioneasierFilterusing0.22-micronfilter(bacteria-eliminating)
IncreasednursingtimeRequirestwosetsoftubingIncreasedbacterialgrowthinlipidsMaximum12-hourhangtimeofseparatelipids
3-in-1 Time-efficientfornursesSinglebagwithsingletubingDecreasedveinirritationInhibitedbacterialgrowth
Shorterstability(1–2days)Complexcompounding(withoutautomatedcompounder)VisualinspectiondifficultEmulsioninstabilityMustfilterusing1.2-micronfilter,not0.22-micronLimitedcompatibilitywithmedicationsCatheter occlusion more common
E. NutritionalComponentsofPNFormulation1. DextroseusedforcompoundingPNisusually70%andcontains3.4kcal/g.Glycerol(orglycerin)is
anothercarbohydratesourcethatprovides4.3kcal/gandisusedinpremixedparenteralproducts(e.g.,ProcalAmine)
2. Fatemulsionisavailableas10%or20%andcontainsabout10kcal/g;alsoavailableasa30%formulationforcompoundingin3-in-1only
3. AAavailableas3%–20%andprovide4kcal/g4. Electrolytesareaddedtomaintainphysiologicserumconcentrations.5. Multivitaminsandtraceelementsareaddedonthebasisoftherecommendeddailyamount.
F. DevelopingaPNRegimenforAdministrationThroughaCentralIntravenousLine1. Determinecaloricrequirements.
a. Forpatientswithabodymassindex(BMI)lessthan30kg/m2,administer25–35kcal/kg/daybasedonactualbodyweight(BMI=(wtinkg)/(htinmeters)2)
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b. IfBMIexceeds30kg/m2,canadminister11–14kcal/kgbasedonactualbodyweightor22–25kcal/kgbasedonIBWi. Alternatively,somepractitionersadvocateusingadjustedbodyweight(ABW)rather
thanIBW.ii. ABW=[(actualweight–IBW)×0.25]+IBW.
c. Permissiveunderfeedinginvolvestheadministrationofabout80%ofcaloricrequirements,anditcanbeconsideredinitially(exceptinpatientswithkidneyfailurerequiringhemodialysis;thesepatientshaveincreasedproteinandcaloricrequirementstomaintainapositivenitrogenbalance).
d. Acommonlyusedmethodistoestimatebasalenergyexpenditure(BEE)usingtheHarris-Benedictequation:i. Men: BEE=66+13.7(wtinkg)+5(htincm)–6.8(ageinyears).ii. Women: BEE=655+9.6(wtinkg)+1.8(htincm)–4.7(ageinyears).
e. Energyexpendituremayalsobeestimatedthroughindirectcalorimetryincriticallyillpatients(seeCriticalCarechapter).
2. Determinefluidrequirements.a. Usually30–35mL/kg/dayor2500–3500mL/day(forpatientswithoutfluidrestrictions)to
maintainurineoutputintherangeof0.5–2mL/kg/hourb. Fluidrequirementsforpatientswithfluidrestrictions(e.g.,kidneyand/orcardiacdysfunction)
shouldbeindividualized.c. DonotusePNforfluidreplacement,butformaintenancefluidonly.
3. Determineprotein(AA)requirements.a. ForpatientswithaBMIlessthan30kg/m2,proteinisusuallyintherangeof0.8–2g/kg/dayon
thebasisofactualbodyweight(maybehigherinburnortraumapatients).i. Maintenance0.8–1g/kg/dayii. Moderatestress1.3–1.5g/kg/dayiii. Severestress1.5–2g/kg/day
b. ForpatientswithaBMI30–40kg/m2,cangive2g/kg/dayproteinbasedonIBW.ForpatientswithaBMIgreaterthan40kg/m2,cangive2.5g/kg/daybasedonIBW
c. Patientswithkidneydysfunctionmayneedaproteinrestrictiontopreventuremia.i. Kidneydysfunctionwithoutdialysis0.5–1g/kg/dayii. Kidneyfailurewithintermittenthemodialysis1.2–1.5g/kg/day(1.5–2.5g/kg/dayif
continuousrenalreplacement)d. Caloriesfromprotein(4kcal/g)shouldbeincludedinthetotalcaloricprovisionstoprevent
overfeeding.e. For3-in-1formulations,thefinalAAconcentrationshouldbe2.5%–4%toprovideadequate
bufferingcapacityandpreventlipidemulsiondestabilization.f. Completeproteinrequirementscanbeprovidedonday1ofPN(i.e.,thereisnoneedtoslowly
titrateuptorecommendedamount).4. Calculateremainingcalories,andadministerabout20%–30%oftotalcaloriesaslipidandthe
remainderasdextrose.a. Makesuredextroserateofadministrationdoesnotexceedthemaximalrateofhepaticoxidation
of4–6mg/kg/minute(maybelowerincriticallyillpatients,somonitorforhyperglycemiaandadjustamountofdextroseprovidedifneeded).i. Initialdextroseamountscanbeintherangeof150–200g/day.ii. Mayneedtoreduceto100–150g/dayinitiallyinpatientswithdiabetesorstress-induced
hyperglycemia;increasegraduallyduringfirst3–4daystogoalsifbloodglucosevaluesarelessthan150mg/dL
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b. Ahigherpercentageofcaloriesfromlipid(upto50%–60%or2.5g/kg/day)canbeprovidedforashorttimeincertaincases(e.g.,hyperglycemia,hypercapnia).
c. Essentialfattyaciddeficiencycanbepreventedbysupplying2%–4%oftotalcaloriesaslipid(canadministerlipidemulsiononceevery1–2weeks).
5. Estimateadailymaintenanceamountofelectrolytes,vitamins,andtraceelements(seebelow).a. ElectrolyteabnormalitiesshouldbeaddressedandcorrectedbeforePNisinitiated.Avoid
replacingelectrolytedeficienciesusingPNinacutelyillpatients.b. Maintenanceelectrolytes(amountswillvaryandshouldbeindividualized)
i. Sodium60–150mEq/day(1–2mEq/kg/day)ii. Potassium40–80mEq/day(1/mEq/kg/day)iii. Phosphate10–40mmol/day(or15mmol/1000kcal)iv. Calcium10–15mEq/day(gluconateispreferredtopreventincompatibilities)v. Magnesium8–20mEq/day(sulfateformispreferredoverchloridetoprevent
incompatibilities)vi. Chlorideandacetatesaltformsshouldbeusedinaratioof1:1or1.5:1(thesesaltformsdo
nothavespecificrecommendedamounts).vii. Electrolyteadjustment
(a) Typicallywillneedincreasedamountsofmagnesium,phosphorus,andK+duringthefirstfewdaysofPNbecauseofICshifts
(b) Chlorideandacetatesaltformscanbeadjustedasneededtomaintainacid-basebalance(seebelowunder“Monitoring”)
c. Standardtraceelementscontainselenium,chromium,copper,manganese,andzinc (e.g.,MTE-5).i. Patientswithhigh-outputfistulas,diarrhea,burns,orlargeopenwoundsmayrequire
additionalzincsupplementation.ii. Patientswithchronicdiarrhea,malabsorption,andshort-gutsyndromemayrequire
additionalseleniumsupplementation.iii. Patientswithseverecholestasisshouldhavecopperandmanganeserestrictedtoprevent
accumulationandtoxicitybecausebothundergobiliaryelimination.d. Parenteralmultivitaminshouldbeaddeddaily(generallycontains150mcgofvitaminK).
i. Additionalthiamine(25–100mg)canbesupplementedinpatientswithahistoryofalcoholabuse.
ii. Duringshortagesofparenteralvitamins,canreducefrequencyofadministrationto3times/weekorcanadministerindividualvitaminsdaily(i.e.,thiamine,ascorbicacid,niacin,pyridoxine,folicacid)ormonthly(i.e.,vitaminB12)
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table 16. CentralPNCalculations
Exampleofacentral3-in-1PNformulafora70-kgpatienthospitalizedwithischemicbowel:(fora2-in-1PNformula,thelipidsarehungseparately)
1.Totalcaloriesestimatedas30kcal/kg×70kg=2100kcal
2.Fluidrequirementsestimatedas1500mL+(20mL/kg×50kg)=2500mL/day
3.Estimatedproteinneedsare1.5g/kg×70kg=105gofprotein.Considerprotein-basedcaloriesaspartoftotalcalories:4kcal/g×105g=420kcalfromprotein.Using10%AA-basedsolution,willneed1050mLtoequal105gofprotein(canroundto1000mLifthismakescompoundingeasier)
4.Determinecaloriesfromfatanddextrose.Totalcaloriesneededis2100kcal−420kcalfromAA=1680remainingcaloriesneeded.Administer25%–30%oftotalkilocaloriesaslipid,orabout500kcalfromlipid.Using10%lipidemulsion,willneed500mLtoequal500kcal(around1kcal/mL)
Totalcaloriesneededis2100kcal−420kcal(AA)−500kcal(lipid)=1180kcalneededfromdextrose.Assuming3.4kcal/g,thenneedaround350gofdextrose.Usinga70%basedextrosesolution,willneed500mLtoequal350gor1190kcal
Calculatetherateofdextroseadministrationinmilligramsperkilogramperminute: [(350g/24hours)×(1000mg/g)×(1hour/60minutes)]/70kg=3.5mg/kg/minute Thisisanappropriaterateofdextroseadministration
5.Finalformulawillcontainthefollowing: AA10%1050mL Lipid10%500mL Dextrose70%500mL Electrolytes,multivitamins,andtraceelements(about100mL) Finalvolumeof2150mLtoinfuseat2150mL/24hour=90mL/hour (Finalvolumeassumespatientisreceivingabout350mLoffluidfromothermedications)
6.FinalconcentrationofmacronutrientsinPNis: AA105g/2150mLfinalvolume=4.9% Lipid50g/2150mL=2.3% Dextrose350g/2150mL=16%
7.FinalcaloricvalueofPNis: AA105g×4kcal/g=420kcal Lipid50g×10kcal/g=500kcal Dextrose350g×3.4kcal/g=1190kcal Totalcalories=420+500+1190=2110kcal/70kg=30kcal/kg 24%oftotalcaloriesareprovidedaslipid
AA=aminoacids;PN=parenteralnutrition.
G. DevelopingaPNRegimenforAdministrationThroughaPeripheralIntravenousLine1. Willlikelynotmeetnutritionalneedsbasedonmacronutrientandmicronutrientconcentration
restrictions(seeabove)2. Foradditionalcalories,increasepercentageofcaloriesadministeredaslipid.
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table 17. PeripheralPNCalculations
Exampleofaperipheral3-in-1PNformulafora70-kgpatient:1.Totalcaloriesestimatedas30kcal/kg×70kg=2100kcal2.Fluidrequirementsestimatedas1500mL+(20mL/kg×50kg)=2500mL/day;prescriberwantsPNto
containnomorethan2000mL3.Calculateamountofdextroseas2000mL×10%=200gofmaximaldextroserecommended4.CalculateamountofAAas2000mL×3%=60gofmaximalAArecommended5.Addabout500kcalaslipid(canaddmoreifpatienttolerates).Canuse10%or20%lipidemulsion6.Calculatevolumesofar.Using70%dextrose,need286mLtoequal200gofdextrose.Using10%AA,
willneed600mLtoequal60g.Using10%lipid,willneed500mL.Willaddelectrolytes,traceelements,multivitamins,andenoughsterilewaterforatotalvolumeof2000mL
7.Finalformulawillcontainthefollowing: AA10%600mL Lipid10%500mL Dextrose70%286mL Electrolytes,multivitamins,andtraceelements Sterilewateraddedfor2000mLfinalvolumetoinfuseat2000mL/24hours=83mL/hour8.FinalconcentrationofmacronutrientsinPNis: AA60g/2000mLfinalvolume=3% Lipid50g/2000mL=2.5% Dextrose200g/2000mL=10%9.FinalcaloricvalueofperipheralPNis: AA60g×4kcal/g=240kcal Lipid50g×10kcal/g=500kcal Dextrose200g×3.4kcal/g=680kcal Totalcalories=240+500+680=1420kcal/70kg=20kcal/kg 35%oftotalcaloriesareprovidedaslipid
H. OrderofMixing(formanualcompounding)1. Adddextrose,AA,sterilewater2. Addphosphate.3. Addotherelectrolytes(exceptCa)andtraceminerals.4. MixwelltoensurephosphateisevenlydistributedandtopreventprecipitationwithCa.5. AddCa.6. Observeforprecipitatesorcontaminants.7. Addlipidif3-in-1formulation.(Note:DonotmixdextroseandlipidsdirectlybecausethelowpHof
dextrosecandestabilizethelipidemulsion.)8. Addvitaminslast,asclosetothetimeofPNadministrationaspossibleinacutecaresettings,orjust
beforeinfusioninpatientsreceivinghomePN.
I. FactorsAssociatedwithCaandPhosphatePrecipitationinPN1. IncreasingpH(morebasic)increasestheriskofCaandphosphateprecipitation.2. IncreasingCaorphosphateconcentrationincreasestheriskofprecipitation.
a. IfCaconcentrationis6mEq/Lorlessandphosphateconcentrationis30mmol/Lorless,theriskof precipitation is low.
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b. CaClismorelikelytoprecipitatewithphosphatethanCagluconate;CaClshouldneverbeusedincompoundingPNformulations.
3. ThefinalconcentrationofAAshouldbeatleast2.5%orhighertopreventCaandphosphateprecipitation.a. AAformsolublecomplexeswithCaandphosphate.b. AAprovideabuffersystemtomaintainalowerpHofthePNinanacceptablerangetoprevent
Ca or phosphate precipitation.4. Asthetemperatureincreases,theriskofprecipitationincreases.
a. PNshouldberefrigeratedifnotadministeredwithin24hoursofcompounding.b. Ifrefrigerated,PNshouldbeadministeredwithin24hoursofrewarming.
5. A1.2-micronfilter(usedfora3-in-1PN)maynotpreventembolismofaCaphosphateprecipitatebutshouldbeusedanywaytoreducetherisk.
6. Orderofmixingadditives(seeabove)7. ThePNshouldbeagitatedoftenduringcompoundingtoensureadequatemixtureintosolution.
J. MedicationAdditivesinPN1. Ingeneral,medicationsshouldnotbeaddedtoPNifitcanbeavoided.2. DonotaddthefollowingtoPN:Ceftriaxone(precipitateswithCa),phenytoin(canchangethepH
ofPN),medicationscontainingpropyleneglycolorethanolasdiluents(e.g.,furosemide,diazepam,lorazepam,digoxin,phenytoin,etoposide),irondextran(trivalentcationsdestabilizethelipidemulsionin3-in-1PNformulations)
3. Incompatibledrugsshouldbeadministeredthroughaseparateintravenouscatheteroraseparatelumenofacentralvenouscatheterifpossible.
4. IfanincompatibleintravenousdrugneedstobeadministeredthroughthesameintravenouscatheterasthePN,thePNshouldbestopped,followedbyacompatibleflushbeforeandafterdrugadministration.ThevolumeofflushshouldbesufficienttocleartheentirecatheterofPNandofdrug(typicallyaround10mLifflushingtheportclosesttothepatient);fordrugsrequiringlongerinfusiontimes,seebelowforprecautionstopreventreboundhyperglycemiawithprolongedinterruptionsofPN.
5. OnlyregularinsuliniscompatiblewithPN.
K. PNComplications1. Catheter-relatedinfectionsareprimarilycausedbyStaphylococcus aureus andCandida albicans.2. Catheterinsertioncomplications(e.g.,pneumothorax,incorrectplacement)3. Peripheralvenousthrombophlebitiscanoccurwithperipheralcatheterplacement;riskisincreasedby
day4ofcatheterization;therefore,siteshouldberotatedevery3days.4. Fluidimbalance5. Acid-baseimbalancesareusuallyrelatedtothepatient’sunderlyingcondition;however,excessiveCl
saltsinthePNcancauseametabolicacidosis,whereasexcessiveacetatesaltsinthePNcancauseametabolicalkalosis.
6. Hyperglycemiacanleadtonosocomialandwoundinfections.7. Gutatrophy8. Overfeedingcancausehepaticsteatosis,hypercapnia(elevatedCO2),hyperglycemia,andazotemia.9. Essentialfattyaciddeficiency
a. Symptomsincludeskindesquamation,hairloss,impairedwoundhealing,hepatomegaly,thrombocytopenia,fattyliver,andanemia.
b. Canoccurwithin1–3weeksofalipid-freePN
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10. Refeedingsyndromecanoccurinacutely(canincludecriticallyillpatients)orchronicallymalnourishedpatientsbyinitiatingENorPN.a. Characterizedbyhypophosphatemia,hypokalemia,hypomagnesemiab. Cancausecardiacdysfunction,respiratorydysfunction,anddeathc. Preventionofrefeedingsyndrome:
i. Identifypatientsatrisk(e.g.,anorexia,alcoholism,cancer,chronicallyill,poornutritionalintakefor1–2weeks,recentunintentionalweightloss,malabsorption)
ii. Initially,providelessthan50%ofcaloricrequirements;thenadvanceoverseveraldaystodesiredgoal.
iii. SupplementvitaminsbeforeinitiatingPNaswellasK+,phosphate,andmagnesium(ifneeded);monitordailyforatleast1week;andreplaceelectrolytesasneeded(manypatientswillneedaggressiveelectrolytereplacementduringthefirstweekofPN).
11. Aluminumtoxicitya. Morelikelytooccurinpatientsonlong-termPNorinthosewithrenaldysfunction(aluminumis
renallyeliminated)b. AccumulatesinboneandinterfereswithboneCauptake,causingosteopeniac. Neurotoxicityd. Aluminumcontaminatesmanyintravenouselectrolytesandintravenousfluids.e. Seedruglabelsforamountofaluminumcontent(mandatedbytheFDA[U.S.FoodandDrug
Administration]).12. Hepatobiliarydisorders(includessteatosis,cholestasis,andgallbladdersludgeorstones)canoccur
withlong-termadministrationofPN.a. Steatosis(orfattyliver)isassociatedwithoverfeedingandatransientelevationin
aminotransferaseconcentration.Althoughitisusuallybenign,itcanprogresstofibrosisorcirrhosisinpatientsreceivinglong-termPN.
b. Cholestasisusuallyoccursinchildren,butitcanalsooccurinadultsreceivinglong-termPNandcanprogresstocirrhosisandliverfailure;aconjugatedbilirubinconcentrationgreaterthan2mg/dListheprimarysign.
c. Gallbladderstasisisassociatedwiththedevelopmentofgallstones,sludge,andcholecystitisandismoreattributabletoalackofENthantoPNadministration.
13. Osteoporosisandosteomalaciacanoccurinpatientsreceivinglong-termPN,andtheyareassociatedwithhigherproteindoses(causesincreasedCaexcretion)andchronicmetabolicacidosis(becauseofinsufficientacetate).
Patient Case9. A43-year-oldmaletraumapatient(wt100kg,ht6′3′′),wasrecentlyextubatedandisreceivingPN.HisPN
formulacontains35kcal/kg,1.2g/kgofprotein,dextroseinfusingat4.4mg/kg/minute,and25%oftotalcaloriesas lipid.Hehasgraduallydevelopedsymptomsofhypercapniaandhasdevelopedarespiratoryacidosis.Themedicalteamisconsideringstrategiestocorrectthistoavoidreintubation.WhichoneofthefollowingchangestothePNformulacouldbestcorrectthissituation?A.ChangePNtoENandmaintaincurrentcaloricgoals.B.ReducedextroseamountinPNto3mg/kg/minuteandincreaselipidtomaintaincurrentcaloricgoal.C.ChangeelectrolytestotheacetatesaltinthePNtocorrecttheacid-baseimbalance.D.Reducethecaloriesto25kcal/kgtopreventoverfeeding.
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L. MonitoringPatientsWhoAreReceivingPN1. Monitorforinfection(temperature,WBC,intravenousaccesssite).2. Monitorforperipheralveinthrombophlebitisand/orinfiltration(ifperipheralaccess);symptoms
includepain,erythema,andtendernessorapalpablecordatthesiteoftheperipheralvein;treatbyremovingcatheter.
3. Monitorfluidstatus(weight,edema,vitalsigns,inputandoutput,temperature).4. Monitor nutritional status.
a. Prealbuminisveryusefulinmonitoringtheeffectsoflong-termnutritionsupportinpatientswhoarenotcriticallyill(seeMonitoringENabove).i. Values
(a) Normalrange16–40mg/dL(b) Moderatemalnutrition11–16mg/dL(c) Severemalnutritionislessthan11mg/dL.
ii. Goalformalnourishedpatientsisanincreaseofatleast3–5mg/dL/weekuntilwithinnormalrange.
b. Serumalbumin(normal3.5–5g/dL)isapoorpredictorofnutritionalstatusbecauseithasalonghalf-lifeandconcentrationsfluctuateduringillness.
5. Monitorforhyperglycemiaandhypoglycemia.a. Acommongoalbloodglucoseis150mg/dLorless,althoughthereisnoconsensusforacutelyill
hospitalizedpatients.b. Regularinsulin(initially0.05–0.2unitofdextrosepergram)canbeaddedtothePNforpatients
usingaconsistentdosage.c. Forpatientswithhyperglycemiaorfluctuatinginsulindosages,insulincanbesupplemented
separatelyfromthePN,althoughthispracticevariesbypractitioner.d. AbruptdiscontinuationofPNisusuallytoleratedinnondiabeticpatients,butrebound
hypoglycemiamayoccurinotherpatients;avoidbygraduallytaperingoffPNover1–2hours;checkbloodglucose30minutesto1hourafterdiscontinuationofPN.IfPNisdiscontinuedabruptly,canavoidreboundhypoglycemiabyadministrationof5%or10%dextrose(unnecessaryifPNisadministeredthroughaperipheralcatheter)
6. Monitorforelectrolyteandacid-baseimbalances.TheClandacetatesaltscanbeadjustedonthebasisoftheacid-basestatusofthepatient.a. Formetabolicalkalosis,NaandK+canbeadministeredastheClsalts.b. Formetabolicacidosis,NaandK+canbeadministeredastheacetatesalts(acetateisconvertedto
bicarbonate).c. Forrespiratoryacid-basedisorders,correcttheunderlyingcauseoradjusttheventilatorsettings
asneeded.7. Monitortriglycerideconcentrationsandwithholdlipidsinpatientswithaconcentrationgreaterthan
400mg/dL.Whencalculatinglipidrequirements,accountforanydrugsmixedinalipidemulsion(e.g.,propofol,clevidipine).
8. Monitor hepatic function.9. MonitorforpatientreadinessfororalorENsupport.
a. Well-nourished,relativelyhealthypatientscanchangeimmediatelyfromPNtooral/EN.b. Elderly,debilitated,and/ormalnourishedpatientsmayneedatransitionperiodinwhichoralor
ENfeedingsaregraduallyincreased,coincidingwithareductioninPN.
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Patient Cases10. Apatientweighing70kgreceivespropofolat45mcg/kg/minute.Propofolisavailableataconcentration
of10mg/mLandismixedina10%lipidemulsion.Assumingthepatientisreceivingthisinfusionratefor24hours,whichofthefollowingbestapproximatesthetotalcaloriesprovidedbythepropofolinfusionina24-hourperiod?A. 200kcal.B. 250kcal.C. 300kcal.D. 500kcal.
11. Apatientwhoweighs65kgisreceivingPNafterabdominalsurgery.ThePNcontainsabout1600kcalin-cluding100gofprotein,500kcalaslipid,and200gofdextrose.Thefollowingadditivesarealsoincludedina24-hourinfusionofPN:NaCl50mEq,Na+acetate100mEq,K+acetate60mEq,Na+ phosphate 30 mmol,magnesiumsulfate12mEq,Ca++gluconate10mEq/day,multivitamins10mL,andseveral traceelements3mL.ThepatienthasanNGtubeinplaceandissuctioningabout400–500mL/day,whichisbe-ingreplacedwithaninfusionof0.9%NaCl.After48hoursofPN,thepatienthasthefollowinglaboratoryvalues:Na+140mEq/L,K+3.8mEq/L,Cl- 93mEq/L,bicarbonate35mEq/L,pH7.5,Pco247mmHg,andbicarbonate36mEq/L.WhichoneofthefollowingadjustmentstothePNformulaisbestatthistime?A. Increaselipidstoprovide750kcalandreducedextroseto130g.B. IncreaseNaacetateto150mEq/dayanddiscontinueNaCl.C. IncreaseNaClto150mEq/dayanddiscontinueNa+ acetate.D. Addsodiumbicarbonate50mEqtoPN.
12. A75-year-old,50-kgwomanisreceivingPNafteranextensivebowelresection.Sheisexpectedtorequireabout1weekofPN.Sheisreceivingthefollowingmacronutrientsinherformula:70%dextrose300mL,10%lipid300mL,and10%AA750mL.Ifthesemacronutrientsareinfusedover24hours,whichofthefollowingmostcloselyapproximatesthetotalcaloriesthatthispatientisreceiving?A. 20kcal/kg.B. 26kcal/kg.C. 30kcal/kg.D. 35kcal/kg.
13. Thepatientinquestion12hasreceivedthePNformulaabovefor3days.Herbloodglucoseconcentrationshaverangedfrom200to280mg/dL.Shehasordersforthefollowingslidingscaleofregularinsulin:bloodglucose200–250give2units,bloodglucose251–300give4units,andbloodglucose301–350give6units.Shehasbeenreceivingabout14–16unitsofinsulindailythroughthesliding-scaleorders.Hermedicalhis-toryissignificantforhypertension,diabetes,chronicobstructivepulmonarydisease,andcoloncancer.Shewasrecentlyinitiatedonmethylprednisolone60mgintravenouslyevery6hoursforachronicobstructivepulmonarydiseaseexacerbation.Today,thedosewillbereducedto40mgintravenouslyevery8hours.Whichoneofthefollowingisthebestrecommendationtobettercontrolthispatient’sbloodglucose?A. Addinsulinglargine10–20units/daytoPN.B. Change70%dextroseinPNtoD5W.C. Increasethesliding-scaleinsulinto4unitsforbloodglucose200–250,8unitsforbloodglucose
251–300,and12unitsforbloodglucose301–350.D. AddNPH(neutralprotamineHagedorn)insulin5–10unitssubcutaneouslyevery12hours.
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7. RoseBD,PostTW.Clinical Physiology ofAcid-BaseandElectrolyteDisorders,5thed.NewYork:McGraw-Hill,2001.
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9. VerbalisJG,GoldsmithSR,GreenbergA,etal.Hy-ponatremiatreatmentguidelines2007:expertpan-elrecommendations.AmJMed2007;120:S1–S21.
10. Vincent JL,WeilMH. Fluid challenge revisited.CritCareMed2006;34:1333–7.
nutrition1. A.S.P.E.N.BoardofDirectors.Guidelinesfor the
use of parenteral and enteral nutrition in adultand pediatric patients. J Parenter Enter Nutr2002;26(Suppl):1SA–138SA.
2. Bankhead R, Boullata J, Brantley S, et al.A.S.P.E.N.EnteralNutritionPracticeRecommen-dations.JParenterEnterNutr2009;33:122.
3. BtaicheIF,KhalidiN.Metaboliccomplicationsofparenteralnutritioninadults,part1.AmJHealthSystPharm2004;61:1938–49.
4. BtaicheIF,KhalidiN.Metaboliccomplicationsofparenteralnutritioninadults,part2.AmJHealthSystPharm2004;61:2050–7.
5. CanadaT,CrillC,GuenterP.A.S.P.E.N.ParenteralNutritionHandbook.SilverSpring,MD:AmericanSocietyofParenteralandEnteralNutrition,2009.
6. Marik PE. Maximizing efficacy from parenteralnutritionincriticalcare:appropriatepatientpopu-lations,supplementalparenteralnutrition,glucosecontrol, parenteral glutamine, and alternative fatsources.CurrGastroenterolRep2007;9:345–53.
7. MirtalloJ,CanadaT,JohnsonD,etal.TaskForcefor the Revision of Safe Practices for ParenteralNutrition.Safepracticesforparenteralnutrition.JParenterEnterNutr2004;28:S39–S70.
8. NewtonDW,DriscollDF.Calciumandphosphatecompatibility: revisited again. Am J Health SystPharm2008;65:73–80.
9. StapletonRD,JonesN,HeylandDK.Feedingcriti-callyillpatients:whatistheoptimalamountofen-ergy?CritCareMed2007;35:S535–S540.
10. Martindale RG, McClave SA, Vanek VW, et al.Guidelines for the provision and assessment ofnutrition support therapy in the adult criticallyill patient: Society of Critical Care MedicineandAmericanSociety for Parenteral andEnteralNutrition: executive summary. Crit Care Med2009;37:1757–61.
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AnSWeRS And eXPLAnAtIOnS tO PAtIent CASeS
1. Answer CAlthoughthispatient’sBPisnotnecessarilylow,it islikelylowcomparedwithhisbaseline,consideringhishistory of hypertension. In addition to his relativelylowBP,hisothersignsandsymptomsofintravascularvolume depletion include an increased BUN/Cr ratioandareducedurineoutput.Crystalloidsorcolloidsareappropriatefluidsforresuscitation,makinghetastarch(Answer C) the best option. Furosemide (Answer A)may increase his urine output, but at the cost of fur-therdepletingtheintravascularvolume.Albumin25%(Answer B) should be avoided for fluid resuscitationbecauseitcausesashiftoffluidfromtheISspaceintotheintravascularspace,whichcanpotentiatehisdehy-dration.AnswerDwouldbeappropriateforamainte-nanceinfusion;however,D5W/0.45%NaClplusKCl20mEq/Lwouldnotprovideoptimal replacementof theintravascularspacegiventhedistributioninTBF.
2. Answer CThispatienthasnocurrentsignsorsymptomsofintra-vascularvolumedepletion,sohedoesnotrequirefluidresuscitation.Becauseheisnottakingadequatefluidsbymouth,heshouldbeadministeredmaintenancein-travenousfluid topreventdehydrationandelectrolyteimbalances.Thisis typicallyaccomplishedbyacom-binationoffreewater(asD5W)and0.45%NaClwithK+.The infusion rate is calculated as 1500mL+ (60kg×20mL/kg)=2700mL/24hoursorabout110mL/hour.Parenteralnutrition(AnswerA)is inappropriatebecausethereisnoevidencethatthepatient’sGItractisnonfunctional.Albumin5%(AnswerB)orLRsolu-tion(AnswerD)shouldbereservedforfluidresuscita-tioninpatientswithsignsorsymptomsofintravascularvolumedepletion.
3. Answer BAlthoughthispatientisexperiencingsymptomatichy-ponatremia,she isalsoshowingsignsof intravascularvolumedepletion.ThisintravascularvolumedepletionisapotentstimulusforADHsecretion,whichwillpo-tentiate hyponatremia. In patients with hyponatremia and intravascular volume depletion, it is important torestore intravascularvolumefirst topreventorganhy-poperfusionaswellastoinhibitthesecretionofADH.Fluid resuscitationshouldbeaccomplishedwith0.9%
NaClasafluidbolus,followedbyareevaluationoffluidstatus.Aslowerinfusionof0.9%NaCl(AnswerA)willnotquicklyrestore intravascularvolume.Once the in-travascular volume is restored, secretionofADHwillcease.ThiscanbefollowedbyawaterdiuresiswithasubsequentriseintheserumNa+concentration.Ofim-portance,thepatientshouldbemonitoredcloselytopre-ventariseinserumNa+greaterthan10–12mEq/L/day.IfserumNa+risestoofast,0.45%NaClcanbeinfusedtoslowtherateofriseofserumNa+concentration.Hy-pertonicsaline(AnswerCandAnswerD)wouldnotbeadvisableunlessthepatientcontinuedtohavesymptomsofhyponatremiaafterappropriatefluidresuscitation.
4. Answer CTopreventcentralpontinemyelinolysisinpatientswithhyponatremia, it is recommended that the serumNa+ concentrationberaisedbynomorethan10–12mEq/Lin24hours.Ofemphasis, thegoalisnottoachieveanormal serum Na+ concentration in 24 hours. Rapidcorrection of chronic hyponatremia can cause perma-nentneurologicdamage.
5. Answer dThis patient has hyponatremia and hypokalemia. Inpatientswith hypokalemia, there is a reduction in ICK+.Tomaintaincellularelectroneutrality,Na+ will shift intocells.AsK+isreplaced,Na+willshiftoutofcells,and theserumNa+ concentrationwill rise.Therefore,inthiscase,thehypokalemiashouldbecorrectedfirst,whichwillcauseasubsequentimprovementinthehy-ponatremia.BecausethispatienthasnoECGchangesrelatedtothehypokalemia,oralsupplementationwithK+isrecommendedoverintravenousreplacement(An-swerA).Adoseof60–80mEq/dayshouldcauseanin-creaseintheK+concentrationofabout1.5mEq/L.Be-causethepatientiseatingaregulardiet,sheshouldnolonger require intravenous fluids (AnswerB).Hyper-tonicsaline(AnswerC)isincorrectbecausethispatientisnotexperiencingserioussymptomsofhyponatremia.
6. Answer dThispatienthasnotbeengivenenoughwater,andsheis unable to communicate (or feel) thirst. Thismedi-cal error can be prevented by administering about 1mLofwater foreverycalorieadministered. It should
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alsobepreventedbymonitoringserumNaconcentra-tionsandadjustingwaterintakeasneeded.Tocorrectthehypernatremia,watershouldbeadministeredpref-erably through the enteral feeding tube. If this is notpossible,thenitcanbereadministeredintravenouslyasD5W(AnswerBorC)butneverassterilewater(An-swerA).Sterilewateradministeredintravenouslycancausehemolysisanddeath.Thepatient’swaterdeficit(inliters)canbeestimatedbytheequation0.4×LBW×[(Na+/140)−1].Watershouldbereplacedoverseveraldays,takingcaretoavoidchangesinserumNa+greaterthan10–12mEq/Lin24hours.
7. Answer BThis patient hasECGchanges consistentwith hyper-kalemia.Insulin(AnswerB)willhavethefastestonsetandmostpredictableactionof loweringserumpotas-sium.Calciumgluconate(AnswerA)shouldbeavoidedinthispatientbecauseitcanpotentiatedigoxintoxicityand bradycardia. The efficacy of sodium bicarbonate(AnswerC)isnotwellestablished.Albuterol(AnswerD)canbeefficaciouswhenaddedtoinsulin,butitmaynotbeeffectiveinabout40%ofpatientsandisthere-fore not recommended as initial therapy or asmono-therapyforhyperkalemia.
8. Answer CThis patient is receiving a calorie-dense EN formulathattypicallyhaslesswaterthanotherenteralproducts.Therefore,althoughsheisnotcurrentlyhypernatremic,thepatient isat riskofdevelopinghypernatremiabe-causeofinsufficientwaterintake.Thiscanbeprevent-ed by administering additional water. The preferredrouteisenteralifpossible.Theadditionalwaterneededonadailybasiscanbeestimatedas1mL/kcal.There-fore, if this patient is receiving the enteral feeding at35mL/hour×2kcal/mL, she is receiving1680kcal/day.Sheisonlyreceiving710mL/Lofwaterofenteralformula,whichamountsto596mL/dayforthe840mLofenteralfeedingdaily(35mL/hour×24hours=840mL/day).Becausesheisreceiving1680kcal,sheneedsabout1680mL/dayofwater.Subtractingthewaterfromthefeedingsfromthetotalneeded,1680−596=1084mL is needed.This can be divided and administeredthroughthegastricfeedingtubeasaround180mL/doseevery4hours.Ofnote,thepatientshouldbemonitoredforfluidoverload,especiallygivenherchronickidneydisease.Giventhispatient’sstablekidneydiseaseand
heradequateurineoutput,sheshouldbeabletotoler-atethisamountoffreewater.Theamountoffreewa-terneededonadailybasisisanestimationandshouldbeadjustedonthebasisofspecificpatientparameters(e.g., serumNa+, input, output, dailyweight, edema).Freewatershouldnotbeadministeredas intravenousdextrose (Answer B) unless enteral administration isnot feasible.AnswerA is incorrect because reducingNawillnotpreventhypernatremia;theproblemisre-latedtotoolittlewaterratherthantoomuchNa+. An-swerDisincorrectbecausethecaloricgoalsshouldnotbesacrificed,andtheywouldnoteliminatetheproblemofinsufficientwateradministered.
9. Answer dThis patient is developing a respiratory acidosis pos-siblybecauseofoverfeeding.Althoughdextroseisme-tabolizedtowaterandCO2,itgenerallywillnotcausearespiratoryacidosisunlessthepatientisbeingoverfed.Therefore,byreducingthetotalcaloriesto25kcal/kg,theriskofoverfeedingisdiminished,andreintubationcanbeavoided.AnswerAisincorrectbecausepatientscanbeoverfedwitheitherPNorEN.AnswerBisin-correctbecauseevenwithreducingthedextroseinthePN, the patient can still develop symptoms of over-feeding.AnswerCisincorrectbecausetheunderlying(overfeeding)causeshouldbecorrected,ratherthanad-justingtheacetatetotreatarespiratoryacidosis.
10. Answer dTodeterminetheamountofcaloriesprovidedbypro-pofol,itmustfirstbedeterminedhowmanymillilitersa day are infused. For this patient receiving 45mcg/kg/minuteofpropofolandweighing70kg,454mLisinfuseddaily(assumingaconstantinfusionrate).Next,assumingthata10%lipidemulsionprovidesabout1.1kcal/mL,itcanbecalculatedthat454mL/dayofpropo-folprovidesaround500kcal/day.
11. Answer CThispatienthasdevelopedametabolicalkalosislikelysecondarytothelossofgastricfluidthroughNGsuc-tioning.The low serumCl- andelevated serumbicar-bonateconcentrationssupportthistheory.Inaddition,the acid base is consistentwith ametabolic alkalosiswith a compensatory respiratory acidosis. The treat-ment in this circumstance is to replace the lost fluidwith0.9%NaCl,whichisbeingdone.Inaddition,Na+
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andK+canbeadministeredas theCl-salt, rather thantheacetatesalt.Forthiscase,onlyNa+isconvertedtoCl-salt,andK+isleftastheacetatesaltinitially.Withdailymonitoring,theratioofCl-toacetatecanbead-justedfurtherifneeded.AnswerBisincorrectbecauseitwould likelyworsen themetabolic alkalosis asNa+ acetateisconvertedtobicarbonate.AnswerAisincor-rectbecausehypercapniaisacompensatoryresponse,nottheprimaryacid-basedisturbance.AnswerDisin-correctforseveralreasons.First,itisneveradvisabletoaddNa+bicarbonatetoPNbecauseofincompatibilityandincreasingtheriskofCa++-phosphate precipitation. Second,Na+bicarbonateistheincorrecttreatmentforametabolicalkalosisbecauseitcanworsenalkalosis.
12. Answer BThetotalcaloriesarecalculatedbyaddingthecaloriesprovidedbydextrose,lipid,andAA.Dextroseprovides714kcal(210g×3.4kcal/g);lipidprovidesabout300kcal(30g×10kcal/g);andAAprovides300kcal(75g×4kcal/g).Addingthesetogetherprovidescaloriesof1314kcal/50kg=26.3kcal/kg.
13. Answer dThis patient’s hyperglycemia could be attributable toeitherstressorcorticosteroids.Becausethecorticoste-roiddoseisbeingtapereddownward,thebloodglucoseconcentrationswillalsolikelydecreasewithtime.Forpatientswithafluctuatingbloodglucoseconcentration,itcanbedifficulttoaddinsulintoPNbecauseitcan-notbeadjustedinatimelymanner.Regardless,AnswerA is incorrect because long-acting insulin should notbeaddedtoPN.IfinsulinisaddedtoPN,itshouldberegularinsulin.Althoughsomeexpertspromote“per-missiveunderfeeding,”AnswerBisincorrectbecauseit would provide insufficient calories for this patient.Sliding scales of insulin can be usefulwhen used inconjunctionwithabaselineofinsulininpatientswithafluctuatingbloodglucoseconcentration.However,aslidingscale(AnswerC)shouldnotbeusedasthepri-maryinterventionforbloodglucosecontrolbecauseitis reactive and fails toprevent hyperglycemia. In ad-dition,theslidingscaledescribedrecommendsinsulinonlywhenthebloodglucosereaches200,whichistoohigh.AnswerDiscorrectbecauseitprovidesabaselineofinsulinthatcanbeadjustedinatimelymannerasthebloodglucoseconcentrationsfluctuateon thebasisofthe patient’s status.
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AnSWeRS And eXPLAnAtIOnS tO SeLF-ASSeSSment QueStIOnS
1. Answer: dThispatientcontinuestohavehypotensionandtachy-cardia, both signs of intravascular volume depletion.TheimprovementinBPandtachycardiaafterafluidbo-lusalsoindicatesintravascularvolumedepletion.Fluidadministrationshouldcontinueuntilthereisnofurtherimprovementinvitalsigns.Patientswithintravascularvolume depletion require a rapid bolus of crystalloid(either0.9%NaClorLR) in theamountof500–1000mL(orabout20mL/kg),followedbyareassessment.Arapidbolusisessentialtopreventorgandysfunctioncausedbyhypoperfusion.Althoughthepatienthaspoorurineoutput,administrationoffurosemide(AnswerA)willworsenvolumedepletion.Asvolumeisreplaced,urineoutputwilllikelyincrease.Administrationof5%albumin in combination with a vasopressor (AnswerB) shouldnotbe the initial treatment as longasvitalsignsareimprovingwiththeadministrationoffluidbo-luseswith 0.9%NaCl. In addition, colloids aremoreexpensive,andthereisnoevidenceshowingimprovedoutcomesforfluidresuscitationcomparedwithcrystal-loids. Furthermore,infusionofalbuminover4hoursis incorrectbecause itwouldnotrestore intravascularvolume rapidly enough to prevent organ dysfunction.IntravenousfluidcontainingD5W(AnswerC)isnotap-propriateforfluidresuscitationregardlessofthebloodglucoseconcentration.
2. Answer AToanswerthisquestion,analligationmustfirstbesetupusing0.9%and23.4%NaCl.If0.9%NaClcontains154mEq/L,then3%shouldcontainaround513mEq/L.Aftercompletingthealligation,thecorrectamountscanbedouble-checkedbyverifyingtheamountofNaClinthepreparedproduct:907mLof0.9%NaClcontains140mEqofNaCl;93mLof23.4%NaClcontains372mEq ofNaCl; therefore, 140mEq + 372mEq = 512mEq/LofNaClinthefinalproduct.Theosmolarityiscalculatedas(3g/100mL)×(1mol/58.5g)×(2Osm/mol)×(1000mOsm/Osm)×(1000mL/L)×0.93=954mOsm/L.Becauseoftheosmoticcoefficient(0.93),theNaCl does not completely dissociate in solution. Al-thoughuseoftheosmoticcoefficientprovidesamoreaccurateosmolarity,itislikelynotclinicallyrelevantincalculatingtheosmolarityofintravenousNaCl.There-fore,itissafetoestimatetheosmolarityofNaClasei-
ther954or1026mOsm/Lbecausethereisnoapparentclinicaldifferencebetweentheseosmolarities.Becausetheosmolarityisgreater than900mOsm/L, theinfu-sionshouldbeadministered throughacentral line, ifpossible,topreventpainandirritation.
3. Answer dInthiscase,hyponatremiaislikelybecauseofconges-tiveheartfailureandhaslikelydevelopedoverapro-longedperiod (not acuteonset).Patientswith chronichyponatremia because of heart failure are typicallyasymptomatic.Rapidcorrectionofchronichyponatre-mia is associatedwith permanent neurologic damagecaused by central pontinemyelinolysis. Furthermore,HScanworsenvolumeoverloadinpatientswithheartfailure.Althoughhyponatremiaisasignofworseningheart failure, correction of hyponatremia in patientswithheartfailuredoesnotimproveoutcomes.Forthesereasons,therisksofcorrectingtheserumsodiumwithHS(AnswerA,AnswerB,andAnswerC)outweighthepotentialbenefits.
4. Answer BPatientswith hyperkalemia andECG changes shouldbetreatedfirstwithCa+forcardiacstability.AfterCa++ administration, other measures can be taken to shiftK+ fromtheECcompartment to theICcompartment.Insulin (AnswerA) can accomplish this; however, inthis hyperglycemic patient, insulin should be admin-isteredwithoutglucose.Sodiumpolystyrenesulfonate(Kayexalate;AnswerC)canbeadministered,butitisnoteffectiveimmediatelyandisthereforenotappropri-ate forfirst-line treatment of symptomatichyperkale-mia.Sodiumbicarbonate (AnswerD) is incorrectbe-causeitdoesnottreatcardiacinstability.
5. Answer CThispatientisnottakingadequatenutritionalintakebe-causeofhermentalstatus.BecauseherGItractisfunc-tional,itshouldbeusedforfeedingtopreventgutmu-cosalatrophy.AnNGornasoduodenalfeedingtubeisappropriate for enteral access for short-term nutritional support.Apercutaneousgastrostomytube(AnswerD)requiresasurgicalprocedureandisusedforlong-termnutritionalsupport.Thepatientshouldreceivebetween25and35kcal/kg/day.ThePNformulas(AnswerAand
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AnswerB)shouldnotbeusedinapatientwithafunc-tionalGItract.AlthoughAnswerBwouldbeanappro-priatePNformulaforperipheraladministration,PNisassociatedwithmorecomplicationsthanEN.
6. Answer CThiscorrectformulaprovidesabout30kcal/kgofcalo-ries, 1.5 g of protein per kilogram (AA), and30%oftotalcaloriesaslipid.AnswerAisincorrectbecauseitprovides1000caloriesaslipid,whichisabout62%ofthe totalcaloriesprovided.AnswerB is incorrectbe-cause itcontainsonly0.8g/kgofAA,an insufficientamountconsideringthepatient’sstressandtheappar-entabsenceofkidneyinjury.AnswerDisincorrectbe-cause it contains too much AA.
7. Answer BThis patient has hypomagnesemia and hypokalemia.Correction of hypokalemia requires correction of hy-pomagnesemiatopreventrenallossofK+.Magnesiumshould be administered slowly to avoid hypotensionand increasedrenalexcretioncausedbyrapidadmin-istration.
8. Answer CEnteralnutritionpreventsgutmucosalatrophyandsub-sequentbacterialtranslocation.BacterialtranslocationisthecrossingofbacteriafromtheGItractintothesystemiccirculation.Enteralnutritionisassociatedwithfewerin-fectiouscomplicationsthanisPN,whichmaybepartlybecauseofareductioninbacterialtranslocation.
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