In a patient with narcotic overdose who is breathing about four times per minute, which acid-base disturbance best fits?

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

Answer: (B)

Hypoventilation from narcotic overdose causes carbon dioxide to accumulate in the blood. Higher CO2 drives the formation of carbonic acid, which dissociates to hydrogen ions and bicarbonate, lowering the pH. So the primary disturbance is respiratory acidosis due to CO2 retention from depressed respiratory drive. In an acute overdose, you’d expect a high PaCO2 with a decreased pH; bicarbonate may still be near normal, with renal compensation developing later if the situation persists. If the patient were hyperventilating, you'd see respiratory alkalosis instead, and metabolic disturbances would involve changes in bicarbonate independent of CO2.