Arterial blood gas shows pH 7.30, PaCO2 50 mmHg, and HCO3- 24 mEq/L. What is the primary disturbance?

• A. Respiratory acidosis
• B. Metabolic acidosis
• C. Respiratory alkalosis
• D. Metabolic alkalosis

Answer: (A)

The key idea is how to interpret ABGs by looking at pH first, then the primary driver of the disturbance. A pH of 7.30 shows acidemia. The PaCO2 is elevated at 50 mmHg, indicating that the acidemia is driven by carbon dioxide retention—a respiratory problem. The bicarbonate is normal at 24 mEq/L, meaning there’s no metabolic compensation yet. Put together, this points to a primary respiratory acidosis. The normal bicarbonate suggests an acute process; if this were chronic, the kidneys would have increased HCO3- to compensate, raising the bicarbonate level. So the best answer reflects respiratory acidosis due to CO2 retention.