ABG Interpretation
(Last Updated - 11/27/2006)
-Step 1:
-Have the pH & pCo2 changed in the same direction? --> If yes then primary d/o is metabolic (See Step 2), if no then primary disorder is respiratory (See Step 3)
-Step 2 (Primary Metabolic D/o):
-Calculate the expected pCo2:
Acidosis: Expected pCo2 = (1.5 * HCo3) + 8 (+/- 2)
Alkalosis: Expected pCo2 = (0.7 * HCo3) + 21 (+/- 2)
-Check for a superimposed respiratory d/o:
pCo2 higher than expected --> superimposed resp acidosis
pCo2 lower than expected --> superimposed resp alkalosis
-Step 3 (Primary Respiratory D/o):
-Determine if the d/o is acute (before renal compensation) or chronic (after renal compensation):
Acute Resp Acidosis: Expected pH change = 0.008 * (pCo2 - 40)
Chronic Resp Acidosis: Expected pH change = 0.003 * (pCo2 - 40)
Acute Resp Alkalosis: Expected pH change = 0.008 * (40 - pCo2)
Chronic Resp Alkalosis: Expected pH change = 0.017 * (40 - pCO2)
***If the actual pH is somewhere b/w the expected pH for acute and chronic, then a superimposed metabolic d/o exists
***Renal compensation takes ~6-12 hrs
-Step 4 (Mixed D/o's):
-pCo2 is abnormal & pH is normal or unchanged or
-pH is abnormal & pCO2 is normal or unchanged
-Normal Values:
pH: 7.36 - 7.44
pCo2: 36 - 44
HCo3: 22 - 26
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