A Step by Step Approach to Interpreting ABG’s:

Step 1: Determine primary abnormality

Determine Acidosis versus alkalosis:

• pH <7.35:>

• pH >7.45: Alkalosis

Step 2: Determine is it is Respiratory or Metabolic:

• For Metabolic disorders remember the Ph changes in the same direction as the Bicarb or Co2.

• For Respiratory disorders remember the Ph changes in the opposite direction as the Bicarb or Co2.

For Example:

• Metabolic Acidosis: Serum pH/Serum Bicarb/Co2 all decreased

• Metabolic Alkalosis: Serum pH/Serum Bicarb/Co2 all increased

• Respiratory Acidosis: Serum pH decreased - Serum Bicarb/Co2 increased

• Respiratory Alkalosis: Serum pH increased - Serum Bicarb/Co2 decreased

Step 3: Determine if the Acidosis/Alkalosis is Partially or Completely Compensated:

Complete Compensation is simple if you remember one key concept. The body only “JUST” compensates back to normal range and then it stops; so if the pH is in normal range, determine which end of normal and that will tell you what the original problem was.

For Example:

Compensated ABG with pH 7.36 (the patient had an acidosis)

Compensated ABG with pH 7.44 (the patient had an alkalosis)

Partial Compensation works the same way only the pH is not yet within normal limits.