A patient is being mechanically ventilated in the synchronized intermittent mandatory ventilation mode at a rate of 4 breaths/min. His spontaneous respirations are 12 breaths/min. He receives a dose of morphine sulfate, and his spontaneous respirations decrease to 4 breaths/min. Which acid-base disturbance will the nurse anticipate occurring?

Rationale: A. Metabolic acidosis is incorrect because metabolic acidosis results from either an accumulation of acids (like lactic acid or ketoacids) or a loss of bicarbonate. In this scenario, the patient’s primary issue is hypoventilation, not a metabolic process. B. Metabolic alkalosis is incorrect because this condition arises from loss of hydrogen ions (e.g., vomiting) or excessive bicarbonate intake. The patient’s reduced respirations do not directly affect metabolic acid-base balance. C. Respiratory acidosis is correct because hypoventilation caused by morphine-induced respiratory depression leads to CO₂ retention. Carbon dioxide combines with water to form carbonic acid, increasing hydrogen ion concentration and lowering blood pH. In this case, the patient’s spontaneous respiratory rate decreased from 12 to 4 breaths/min, significantly reducing alveolar ventilation and causing CO₂ buildup, resulting in respiratory acidosis. D. Respiratory alkalosis is incorrect because respiratory alkalosis occurs when hyperventilation causes excessive exhalation of CO₂, decreasing hydrogen ion concentration and increasing blood pH. Here, the patient’s respirations are decreased, not increased, so respiratory alkalosis is unlikely.