The nurse reviews arterial blood gas results showing pH 7.21, pCO2 75 mmHg, and HCO3 32 mEq/L. The nurse concludes the client is most likely experiencing which acid–base disturbance?

• A. Respiratory acidosis that is partially compensated
• B. Metabolic acidosis
• C. Respiratory alkalosis
• D. Metabolic alkalosis

Answer: (B)

An acidemia with a high CO2 points to a respiratory cause. The pCO2 of 75 mmHg shows the patient is hypoventilating and retaining carbon dioxide, which drives the acidity. The bicarbonate is elevated at 32 mEq/L, indicating the kidneys have started to compensate by retaining more bicarbonate to buffer the excess acid. Because the pH is still acidic, the compensation is partial rather than complete, which is typical for a respiratory acidosis with metabolic (renal) compensation.

Metabolic acidosis would require a low bicarbonate level, not a high one, and metabolic alkalosis would raise pH, not lower it. Respiratory alkalosis would show a low pCO2. Therefore, this pattern fits respiratory acidosis with partial compensation.