Arterial blood gases

 

Approach to Arterial Blood Gases

 

Classify the acid-base disturbance based on pH.

 

Anion gap

Increased anion gap in metabolic acidosis; decreased in hypoalbuminemia, paraproteinemia, halide ingestion, lab error)

anion gap = Na+ = Cl- - HCO3    ;    normal is <8-12


 

Assess for compensation

Δ in HCO3 should equal the Δ in anion gap

Δ in HCO3 should equal Δ in PCO2 x correction factor of xxx

 

If PCO2 is not available, can calculate by

If over 10% error, then one of the values is wrong

 

 

 

Converting pH and H+

Log rule

pH = -log[H+]

ie pH 7.4 = 10-7.4 mol/L H+ = 40

 

pH - [H+] rule of thumb

 

For a pH range of 7.25-7.55

drop the 7.

subtract from 80

 

ie pH 7.38 = 42

 

the 0.1 pH change rule

x 0.8 for every increase of 0.1 in pH

/ 0.8 for every decrease of 0.1 in pH

 

pH 7.00 = 100 nM H+

ph 7.4 = 40 nM H+

 

 

arterial blood gas sampling (Dalhousie University Common Common Currency)