An ABG result shows pH of 7.35, PaCO2 of 30 mm Hg, and HCO3– of 18 mEq/L. What com-pensatory measure has the body taken to at least partially compensate for the acid-base disorder?

a. Blown off CO2
b. Retained HCO3–
c. Retained H+
d. Not enough information to determine

ANS: A
The patient has a compensated metabolic acidosis. This is characterized by a low HCO3–, a pH between 7.35 and 7.39, and a low PaCO2. The compensatory response (decreased PaCO2) has restored the pH to the low normal range.