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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