Interpret the arterial blood gas with pH 7.42, PaCO2 50 mmHg, HCO3- 30 mEq/L. How should this be interpreted?

• A. Fully compensated respiratory acidosis
• B. Partially compensated metabolic acidosis
• C. Acute respiratory alkalosis
• D. Uncompensated metabolic alkalosis

Answer: (A)

The main idea is recognizing a primary respiratory problem with metabolic healing. The PaCO2 is elevated at 50 mmHg, indicating hypoventilation and a respiratory acidosis. The bicarbonate is elevated at 30 mEq/L, which shows the kidneys have compensated by retaining bicarbonate to offset the acid buildup. Because the pH is still within the normal range (7.35–7.45) despite the high CO2, this indicates the acid-base balance has been fully restored through metabolic (renal) compensation. The combination of elevated CO2 with an appropriately increased HCO3− and a normal pH pattern fits a fully compensated respiratory acidosis, most consistent with a chronic process rather than an acute one.