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 morphine sulfate, and his spontaneous respirations decrease to 4 breaths/min. Which acid-base disturbance will the nurse anticipate occurring?

A. Metabolic acidosis results from increased acid production, decreased acid excretion, or bicarbonate loss (e.g., diabetic ketoacidosis, renal failure, diarrhea). The scenario describes hypoventilation due to opioid-induced respiratory depression, which is a respiratory problem, not a metabolic one. B. Respiratory alkalosis occurs when there is hyperventilation, leading to excessive carbon dioxide elimination (PaCO₂ 45 mm Hg) and lowering pH. Morphine sulfate depresses the patient’s spontaneous respirations from 12 to 4 breaths per minute, significantly reducing CO₂ elimination. Since the SIMV rate is low (4 breaths/min), total ventilation is inadequate, leading to CO₂ accumulation and respiratory acidosis.