Severe respiratory depression after epidural morphine in a patient with myotonic dystrophy

We describe a patient with myotonic dystrophy who underwent cholecystectomy, and developed severe respiratory depression following epidural administration of morphine to provide postoperative analgesia. At preoperative assessment, he demonstrated near normal vital capacity and maximal voluntary ventilation, but the presence of chronic ventilatory failure with a resting value of PaCO2 51 mmHg. Anaesthesia was produced by a combination of epidural and light general anaesthesia without intravenous anaesthetics, narcotics or neuromuscular relaxants. Five hours after epidural administration of 2 mg morphine, the patient developed severe respiratory depression with a PaCO2 of 93 mmHg. Intravenous naloxone resulted in transient improvement in minute volume, suggesting that epidural morphine was responsible for the depression. Epidural morphine can cause unexpected respiratory depression, even at a small dose, because of the sensitivity of the respiratory centre to morphine in patients with myotonic dystrophy.