This man has a respiratory acidosis. Overdose with drugs that suppress ventilation (e.g., heroin, morphine, barbiturates, methaqualone, and "sleeping pills") often causes hypercapnia. In patients with an intact renal response, the respiratory acidosis causes a compensatory rise in plasma HCO3-, which lessens the fall in pH. However, the renal response requires several days to develop fully. The plasma HCO3- of 26 mEq/L (normal: 22-28 mEq/L) for this man is typical of acute respiratory acidosis with little or no renal compensation. pH 7.34, PaCO2 (mm Hg) 29, HCO3- (mEq/L) 15 reflects metabolic acidosis. pH 7.40, PaCO2 (mm Hg) 40, HCO3- (mEq/L) 24 is normal. pH 7.47, PaCO2 (mm Hg) 20, HCO3- (mEq/L) 14 reflects respiratory alkalosis.