29224520 arterial blood gases 1

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    Arterial Blood GasesArterial Blood Gases

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    ObjectivesObjectives

    Review of physiologyReview of physiology

    Basic interpretation of ABGsBasic interpretation of ABGs

    Radial ABG techniqueRadial ABG technique

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    Some DefinitionsSome Definitions

    pH: concentration of H+ in terms ofpH: concentration of H+ in terms of1010--xx per litreper litre

    pH of 7.0 = 10pH of 7.0 = 10--77

    = 0.0000001= 0.0000001 pH of 6.0 = 10pH of 6.0 = 10--66 = 0.000001= 0.000001

    Acidosis: acidic blood; increase in H+Acidosis: acidic blood; increase in H+concentration (therefore decrease inconcentration (therefore decrease inpH)pH)

    Alkalosis: alkalotic blood; increase inAlkalosis: alkalotic blood; increase inbase, therefore decrease in H+base, therefore decrease in H+

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    Basic principlesBasic principles

    Human bodies were designed toHuman bodies were designed tomaintain:maintain:

    pH 7.35-7.45

    PaO2 95-100mmHg

    PaCO2 35-45

    mmHgHCO3 22-26

    mmHg

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    BuffersBuffers

    Limit pH changes when strongLimit pH changes when strongacids/bases are introducedacids/bases are introduced

    Weak acid and its conjugate baseWeak acid and its conjugate base Addition of a strong acid is partlyAddition of a strong acid is partly

    neutralized by the weak baseneutralized by the weak base

    HB (weak acid) H+ (strong acid) B- (conjugate weak base)

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    Bicarbonate BufferSystemBicarbonate BufferSystem

    CO2+H20 H2CO3 H++HCO3-

    Main extracellular bufferMain extracellular buffer

    Also affected by lungs and kidneysAlso affected by lungs and kidneys

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    Key EquationKey Equation

    CO2+H20 H2CO3 H++HCO3-

    Blood (instantaneously)

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    Key EquationKey Equation

    CO2+H20 H2CO3 H++HCO3-

    Lungs

    (within minutes)

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    Key EquationKey Equation

    CO2+H20 H2CO3 H++HCO3-

    Excretion via kidneys(hours to days)

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    Key EquationKey Equation

    CO2+H20 H2CO3 H++HCO3-

    Blood (instantaneously)

    Lungs

    (within minutes)

    Excretion via kidneys(hours to days)

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    Respiratory AcidosisRespiratory Acidosis

    CO2+H20 H2CO3 H++HCO3-

    Increase in CO2 pushes balance towardsIncrease in CO2 pushes balance towardsproducing more H2CO3producing more H2CO3

    Concentration of H+ increases, loweringConcentration of H+ increases, loweringpHpH

    CausesCauses Impaired lung functionImpaired lung function

    Decreased respiratory driveDecreased respiratory drive

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    Respiratory AlkalosisRespiratory Alkalosis

    CO2+H20 H2CO3 H++HCO3-

    Increased RR causes decreased CO2Increased RR causes decreased CO2

    Balance shifts towards leftBalance shifts towards leftdecreasing concentration of H+decreasing concentration of H+(therefore increasing pH)(therefore increasing pH)

    CausesCauses Hyperventilation (anxiety)Hyperventilation (anxiety)

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    Metabolic AcidosisMetabolic Acidosis

    CO2+H20 H2CO3 H++HCO3-

    Abnormal metabolism releases H+,Abnormal metabolism releases H+,

    increasing concentration of pH, andincreasing concentration of pH, anddecreasing pHdecreasing pH

    CausesCauses

    DKA, lactic acidosis (arrest)DKA, lactic acidosis (arrest) ToxinsToxins

    Loss of HCO3 in diarrheaLoss of HCO3 in diarrhea

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    Metabolic AlkalosisMetabolic Alkalosis

    CO2+H20 H2CO3 H++HCO3-

    I

    ncreased plasma HCO3I

    ncreased plasma HCO3-- neutralizesneutralizesH+H+

    Decreased concentration of H+Decreased concentration of H+

    Causes:Causes:

    Loss of H+ in vomitLoss of H+ in vomit

    Gain of HCO3 (ingestion, IV)Gain of HCO3 (ingestion, IV)

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    Interpreting the ABGsInterpreting the ABGs

    Remember the normalsRemember the normals

    pH 7.4, PaCO2 40, HCO3 24pH 7.4, PaCO2 40, HCO3 24

    Know the expected compensationKnow the expected compensation

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    CompensationCompensationDisorder Initial change Compensation

    MetabolicAcidosis

    Decrease HCO3 1 mmHg decrease inPaCO2 for every 1decrease in HCO3

    MetabolicAlkalosis

    Increase HCO3 0.3-0.5 mmHg increasein PaCO2 for every 1increase in HCO3

    Respiratoryalkalosis

    Decrease inPaCO2

    Acute: 2 decrease inHCO3 for every 10

    decrease in PaCO2Chronic: 4-5 decrease

    Respiratoryacidosis

    Increase inPaCO2

    Acute: 1 increase inHCO3 for every 10increase in PaCO2

    Chronic: 3 increase

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    CompensationCompensationDisturbance PaCO2 HCO3

    Resp acidosis(acute)

    10 1

    Resp acidosis

    (chronic)

    10 3

    Resp alkalosis(acute)

    10 2

    Resp alkalosis(chronic)

    10 4

    Metabolicacidosis

    1 1

    Metabolicalkalosis

    3 10

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    Basic ApproachBasic Approach

    Is the pH acidemic or alkalemic?Is the pH acidemic or alkalemic?

    What is the primary disturbance?What is the primary disturbance?

    Metabolic: change in HCO3 and pH inMetabolic: change in HCO3 and pH insame directionsame direction

    Respiratory: change in PaCO2 and pH inRespiratory: change in PaCO2 and pH inopposite directionopposite direction

    Is the compensation appropriate?Is the compensation appropriate?

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to24 yo M hx of drug abuse, brought toER cyanoticER cyanotic

    pH 7.08pH 7.08 PaCO2 80PaCO2 80

    PaO2 37PaO2 37

    HCO3 26HCO3 26

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to24 yo M hx of drug abuse, brought toER cyanoticER cyanotic

    pH 7.08pH 7.08 PaCO2 80PaCO2 80

    PaO2 37PaO2 37

    HCO3 26HCO3 26

    Acidemic or Alkalemic?Acidemic or Alkalemic?

    AcidemicAcidemic

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to24 yo M hx of drug abuse, brought toER cyanoticER cyanotic

    pH 7.08pH 7.08 PaCO2 80PaCO2 80

    PaO2 37PaO2 37

    HCO3 26HCO3 26

    pH in relation to PaCO2 and HCO3?pH in relation to PaCO2 and HCO3?

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    Basic ApproachBasic Approach

    Is the pH acidemic or alkalemic?Is the pH acidemic or alkalemic?

    What is the primary disturbance?What is the primary disturbance?

    Metabolic: change in HCO3 and pHMetabolic: change in HCO3 and pHin same directionin same direction

    Respiratory: change in PaCO2 andRespiratory: change in PaCO2 andpH in opposite directionpH in opposite direction

    Is the compensation appropriate?Is the compensation appropriate?

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to24 yo M hx of drug abuse, brought toER cyanoticER cyanotic

    pH 7.08pH 7.08 PaCO2 80PaCO2 80

    PaO2 37PaO2 37

    HCO3 26HCO3 26

    primarily respiratoryprimarily respiratory

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to24 yo M hx of drug abuse, brought toER cyanoticER cyanotic

    pH 7.08pH 7.08

    PaCO2 80PaCO2 80

    PaO2 37PaO2 37

    HCO3 26HCO3 26

    Is the compensation adequate?Is the compensation adequate?

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    Case 1Case 1

    PaCO2 increased by 40PaCO2 increased by 40

    For every 10 increase you wouldFor every 10 increase you would

    expect 1 increase in HCO3expect 1 increase in HCO3 Expected HCO3 would be ~28Expected HCO3 would be ~28

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    Case 1Case 1

    24 yo M hx of drug abuse, brought to ER24 yo M hx of drug abuse, brought to ERcyanoticcyanotic pH 7.08pH 7.08

    PaCO2 80PaCO2 80 PaO2 37PaO2 37

    HCO3 26HCO3 26

    Acidemic, primarily respiratory, but mildAcidemic, primarily respiratory, but mild

    component of metaboliccomponent of metabolic Also hypoxemicAlso hypoxemic

    Narcotic ODNarcotic OD

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    Case 2Case 2

    42 F IDDM, presents with 4d hx of unwell42 F IDDM, presents with 4d hx of unwell

    pH 7.23pH 7.23

    PaCO2 27PaCO2 27

    PaO2 118PaO2 118

    HCO3 12HCO3 12

    Acidemia, metabolicAcidemia, metabolic

    DKA, Na 135, Cl 99DKA, Na 135, Cl 99 AG = NaAG = Na ClCl HCO3 = 135HCO3 = 135 111 = 24111 = 24

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    Case 3Case 3

    71 m hx of COPD, c/o SOB71 m hx of COPD, c/o SOB

    pH 7.21pH 7.21

    PaCO2 75PaCO2 75 PaO2 41PaO2 41

    HCO3 30HCO3 30

    Acidemia, resp (acute on chronic),Acidemia, resp (acute on chronic),hypoxichypoxic

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    Case 4Case 4

    23 F c/o SOB, lightheaded and23 F c/o SOB, lightheaded andperioral tinglingperioral tingling

    pH 7.54pH 7.54

    PaCO2 22PaCO2 22

    PaO2 115PaO2 115

    HCO3 21HCO3 21

    Alkalemia, resp (acute)Alkalemia, resp (acute)

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    Case 5Case 5

    32 M c/o vomitting x 5d, HR 110 BP32 M c/o vomitting x 5d, HR 110 BP90/50, dry MM90/50, dry MM

    pH 7.50pH 7.50

    PaCO2 47PaCO2 47

    PaO2 80PaO2 80

    HCO3 38HCO3 38

    Alkalemia, metabolicAlkalemia, metabolic

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    ABG SamplingABG Sampling

    IndicationsIndications

    Assessment of illness, or response toAssessment of illness, or response totherapytherapy

    ContraindicationsContraindications

    Positive Allens testPositive Allens test

    Overlying infectionOverlying infection

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    ABG samplingABG sampling

    SitesSites

    Radial artery, brachial, femoralRadial artery, brachial, femoral

    ComplicationsComplications Arterial spasmArterial spasm

    Hemorrhage/hematomaHemorrhage/hematoma

    Nerve injuryNerve injury

    infectioninfection

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    Allens testAllens test

    AnatomyAnatomy

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    Allens testAllens test

    Step 1: tight fist x 20 secStep 1: tight fist x 20 sec

    Step 2: Occlude radial and ulnar arteriesStep 2: Occlude radial and ulnar arteries

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    Allens testAllens test

    Step 3: open hand and look forStep 3: open hand and look forblanchingblanching

    Step 4: release ulnar artery and lookStep 4: release ulnar artery and look

    for capillary refill (5for capillary refill (5--7 sec)7 sec)

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    ABG techniqueABG technique

    Position wristPosition wrist

    Prep skinPrep skin

    Insert needle ~45Insert needle ~45degrees, bevel updegrees, bevel up

    Apply pressure xApply pressure x5min post5min post

    procedureprocedure