Fluid & Electrolytes Fluid & Electrolytes ManagementManagement

Component & composition of body fluid

Mechanisms of fluid homeostasis

Parenteral fluid therapy

Fluid and electrolyte balance is an extremely complicated thing.

4

5

6

7

8

Solutes – dissolved particlesElectrolytes – charged particles Cations – positively charged ions

Na+, K+ , Ca++, H+

Anions – negatively charged ionsCl-, HCO3

- , PO43-

Non-electrolytes - Uncharged Proteins, urea, glucose, O2, CO2

Composition of Body Fluids:Composition of Body Fluids:

Ca 2+

Mg 2+

K+

Na+

Cl-

PO43-

Organic anion

HCO3-

Protein

0

50

50

100

150

100

150

Cations Anions

EC

FICF

Osmolarity = solute/(solute+solvent)Osmolarity = solute/(solute+solvent) Osmolality = solute/solvent (290~310mOsm/L)Osmolality = solute/solvent (290~310mOsm/L) Tonicity = effective osmolalityTonicity = effective osmolality Plasma osmolility = 2 x (Na) + (Glucose/18) + (Urea/2.8)Plasma osmolility = 2 x (Na) + (Glucose/18) + (Urea/2.8) Plasma tonicity = 2 x (Na) + (Glucose/18)Plasma tonicity = 2 x (Na) + (Glucose/18)

10

12

Regulation of Fluids:Regulation of Fluids:

Renal sympathetic nerves

Renin-angiotensin-

aldosterone system

Atrial natriuretic peptide (ANP)

GI secretionsVolume (ml) per day

• Saliva 1500• Gastric 2500• Bile 500 • Pancreatic 700• Intestinal 3000• TOTAL 8000

Composition of GI Composition of GI Secretions:Secretions:

SourceSource Volume Volume (ml/24h)(ml/24h) NaNa+*+* KK++ ClCl-- HCOHCO33

--

SalivarySalivary1500 (500~2000)

10 (2~10)26 (20~30)

10 (8~18) 30

StomachStomach1500 (100~4000)

60 (9~116)10 (0~32)

130 (8~154)

0

DuodenuDuodenumm

100~2000 140 5 80 0

IleumIleum 3000140 (80~150)

5 (2~8)104 (43~137)

30

ColonColon 100-9000 60 30 40 0

PancreasPancreas 100-800140 (113~185)

5 (3~7) 75 (54~95) 115

Bile Bile 50-800145 (131~164)

5 (3~12)100 (89~180)

35

* Average concentration: mmol/L

Crystalloid solutions –

clear fluids made up of water and electrolyte solutions; Will cross a semi-permeable membrane e.g Normal, hypo and hypertonic saline solutions; Dextrose solutions; Ringer’s lactate and Hartmann’s solution.

Colloid solutions – Gelatinous solutions containing particles suspended in solution. These particles will not form a sediment under the influence of gravity and are largely unable to cross a semi-permeable membrane. e.g. Albumin, Dextrans, Hydroxyethyl starch [HES]; Haemaccel and Gelofusine

Saline Solutions(1) 0.9% Normal Saline – Think of it as ‘Salt and water’

Principal fluid used for intravascular resuscitation and replacement of salt loss e.g diarrhoea and vomitingContains: Na+ 154 mmol/l, K+ - Nil, Cl- - 154 mmol/l; But K+ is often added

IsoOsmolar compared to normal plasmaDistribution: Stays almost entirely in the Extracellular space Of 1 litre – 750ml Extra cellular fluid; 250ml intravacular fluidSo for 100ml blood loss – need to give 400ml N.saline [only 25% remains intravascular]

(2) 0.45% Normal saline = ‘Half’ Normal Saline = HYPOtonic salineReserved for severe hyperosmolar states E.g. severe dehydrationLeads to HYPOnatraemia if plasma sodium is normalMay cause rapid reduction in serum sodium if used in excess or infused too rapidly. This may lead to cerebral oedema and rarely, central pontine demyelinosis ; Use with caution!

(3) 1.8, 3.0, 7.0, 7.5 and 10% Saline = HYPERtonic salineReserved for plasma expansion with colloidsIn practice rarely used in general wards; Reserved for high dependency, specialist areasDistributed almost entirely in the ECF and intravascular space. This leads to an osmotic gradient between the ECF and ICF, causing passage of fluid into the EC space. This fluid distributes itself evenly across the ECF and intravascualr space, in turn leading to intravascular repletion. Large volumes will cause HYPERnatraemia and IC dehydration.

Dextrose solutions(1) 5% Dextrose (often written D5W) – Think of it as ‘Sugar

and Water’Primarily used to maintain water balance in patients who are not able to take anything by mouth; Commonly used post-operatively in conjuction with salt retaining fluids ie saline; Often prescribed as 2L D5W: 1L N.Saline [‘Physiological replacement’ of water and Na+ losses]Provides some calories [ approximately 10% of daily requirements]Regarded as ‘electrolyte free’ – contains NO Sodium, Potassium, Chloride or CalciumDistribution: <10% Intravascular; > 66% intracellularWhen infused is rapidly redistributed into the intracellular space; Less than 10% stays in the intravascular space therefore it is of limited use in fluid resuscitation. For every 100ml blood loss – need 1000ml dextrose replacement [10% retained in intravascular spaceCommon cause of iatrogenic hyponatraemia in surgical patient

(2) Dextrose saline – Think of it as ‘a bit of salt and sugar’Similar indications to 5% dextrose; Provides Na+ 30mmol/l and Cl- 30mmol/l Ie a sprinkling of salt and sugar!Primarily used to replace water losses post-operativelyLimited indications outside of post-operative replacement – ‘Neither really saline or dextrose’; Advantage – doesn’t commonly cause water or salt overload.

Colloid solutionsThe colloid solutions contain particles which do not readily cross semi-permeable membranes such as the capillary membraneThus the volume infused stays (initially) almost entirely within the intravascular space Stay intravascular for a prolonged period compared to crystalloidsHowever they leak out of the intravascular space when the capillary permeability significantly changes e.g. Severe trauma or sepsisUntil recently they were regarded as the gold standard for intravascular resuscitation (see next slide)Because of their gelatinous properties they cause platelet dysfunction and interfere with fibrinolysis and coagulation factors (factor VIII) – thus they can cause significant coagulopathy in large volumes.

Fluid & electrolyte balance

Fluid replacement1. Maintenance requirement2. Replacement of losses3. Ongoing losses

Volume Deficit-Clinical Types

Total body water: Water loss (diabetes insipidus, osmotic diarrhea)

Extracellular: Salt and water loss ( ascites, edema) Third spacing

Intravascular: Acute hemorrhage

Replacement of losses

1. Actual losses Bleeding Vomiting/diarrhoea

2. Ongoing losses Stoma Drains Fistulae NGT U/O

Parenteral Fluid Therapy:Parenteral Fluid Therapy:

Crystalloids:Crystalloids: - contain Na as the main osmotically active particle - useful for volume expansion (mainly interstitial space) - for maintenance infusion - correction of electrolyte abnormality

Crystalloids:Crystalloids:

Isotonic crystalloids - Lactated Ringer’s, 0.9% NaCl - only 25% remain intravascularly

Hypertonic saline solutions - 3% NaCl

Hypotonic solutions - D5W, 0.45% NaCl - less than 10% remain intra- vascularly, inadequate for fluid resuscitation

Colloid Solutions:Colloid Solutions:

Contain high molecular weight substancesdo not readily migrate across capillary walls

Preparations - Albumin: 5%, 25% - Dextran - Gelifundol

- Haes-steril 10%

SolutionSolutionss

VolumeVolumess

NaNa++ KK++ CaCa2+2+ MgMg2+2+ ClCl-- HCOHCO33-- DextroseDextrose mOsm/LmOsm/L

ECFECF 142 4 5 103 27 280-310

Lactated Lactated Ringer’sRinger’s

130 4 3 109 28 273

0.9% 0.9% NaClNaCl

154 154 308

0.45% 0.45% NaClNaCl

77 77 154

D5WD5W

D5/0.45% D5/0.45% NaClNaCl

77 77 278 406

3% NaCl3% NaCl 513 513 1026

6% Hetast6% Hetastarcharch 500 154 154 310

5% 5% AlbuminAlbumin

250,500130-160

<2.5

130-160

330

25% 25% AlbuminAlbumin

20,50,100

130-160

<2.5

130-160

330

Common parenteral fluid therapyCommon parenteral fluid therapy

The Influence of Colloid & The Influence of Colloid & Crystalloid on Blood Volume:Crystalloid on Blood Volume:

1000cc

500cc

500cc

500cc

200

600

1000

Lactated Ringers

5% Albumin

6% Hetastarch

Whole blood

Blood volumeInfusion volume

Example of IVF order

Maintenance (patient of average weight): 1L N/S + 20mmol KCl 1L 4% Dex N/5 + 20mmol KCl 1L 4% Dex N/5 + 20mmol KCl

Note: Gastric outlet obstruction – N/S + KCl SBO – Hartmann’s solution Most of ongoing “surgical” losses are rich in Na

Your fluid chart should look something like this. (I have written it out twice as I was unconvinced of my first attempt)

Maintenance

VariableUsually 2.5-3L/day

Rough guide: 2-3mmol

NaCl/kg/day 1-2mmol K/kg/day

Volume Electrolytes

Fluid Management:Fluid Management:

Goal:Goal: - to maintain urine output of 0.5~1.0ml/kg/h

Electrolytes require:Electrolytes require: - Na+: 1-2mmol/kg/day - K+: 0.5~1.0mmol/kg/day

Avoid fluid overload, especially in malnutrition,

heart failure and renal insufficiency patient

Fluid Management:Fluid Management:

For acute blood lossFor acute blood loss - Begin with 2-3L isotonic crystalloid to restore blood pressure and peripheral perfusion - Early use of colloid - Crystalloid + 5% albumin in a ratio of

4:1 - Blood transfusion - Large borne IV line