Blood Gas AnalysisNo click
The Blood Gas Report: normals…
pH 7.40 + 0.05PaCO2 40 + 5 mm HgPaO2 80 - 100 mm Hg
HCO3 24 + 4 mmol/L
O2 Sat >95Always mention and see FIO2
The essentials
HCO3
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Bicarbonate:
Henderson - Hasselbach equation:
pH = pK + Log HCO3
Dissolved CO2
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20 × 5 = 100
Expected PaO2 =
FiO2 × 5 = PaO2
Normal situation
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5The
Steps forSuccessfulBlood Gas
Analysis
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Step 2 Who is responsible for this change in pH ( culprit )? CO2 wil l change pH in opposite direction Bicarb. wil l change pH in same directionAcidemia: With HCO3 < 20 mmol/L = metabolic
With PCO2 >45 mm hg = respiratory
Alkalemia: With HCO3 >28 mmol/L = metabolicWith PCO2 <35 mm Hg = respiratory
Step 1Look at the pHIs the patient acidemic pH < 7.35or alkalemic pH > 7.45
Step 3If there is a primary respiratory disturbance, is it acute ?
.08 change in pH ( Acute )
.03 change in pH ( Chronic )
10 mm Change PaCO2
=
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Step 4I f the disturbance is metabolic is the respiratorycompensation appropriate?For metabolic acidosis:Expected PaCO2 = (1.5 x [HCO3]) + 8 ) + 2 or simply…expected PaCO2 = last two digits of pH
For metabolic alkalosis:Expected PaCO2 = 6 mm for 10 mEq. r ise in Bicarb.
Suspect if . . . . . . . . . . . . . actual PaCO2 is more than expected :
addit ional …respiratory acidosis actual PaCO2 is less than expected :
addit ional …respiratory alkalosis
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Step 4 cont.I f there is metabolic acidosis, is there a wide anion gap ?
Na - (Cl -+ HCO3-) = Anion Gap usually <12
If >12, Anion Gap Acidosis : M ethanolU remiaD iabetic KetoacidosisP araldehydeI nfection (lact ic acid)E thylene GlycolS alicylate
Common causes1) Lactic acidosis2) Metabolic disorders3) Renal failure
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th step
Clinical correlation5
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HCO3 META.pH
PaCO2 pH RESP.
Same direction
Opposite direction
Same direction
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Remember the format
pHPaCO2
PaO2
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