Interpret the arterial blood gas: pH 7.25, PaCO2 60 mmHg, HCO3- 28 mEq/L.

• A. Primary metabolic acidosis with partial metabolic compensation
• B. Primary respiratory acidosis with partial metabolic compensation
• C. Metabolic alkalosis with respiratory compensation
• D. Combined metabolic and respiratory acidosis

Answer: (B)

High PaCO2 with acidemia indicates the primary problem is respiratory in origin. The pH is low, showing acidemia, and the elevated PaCO2 confirms hypoventilation as the driving cause. The bicarbonate is elevated (above normal), which shows the kidneys have started to compensate for the respiratory acid it’s producing, buffering some of the excess acid. Because the pH remains acidic, the compensation is only partial, not a full chronic correction.

If the primary issue were metabolic, you’d expect a low HCO3- with acidemia or a high HCO3- with alkalemia, not an elevated CO2 as the main driver. A combined metabolic and respiratory derangement would typically push the pH even lower or show a conflicting pattern between CO2 and bicarbonate, which isn’t the case here.