A 56-year-old man undergoes a left upper lobectomy. An epidural catheter is inseed for postoperative pain relief. Ninety minutes after the first dose of epidural morphine, the patient complains of itching and becomes increasingly somnolent. Blood-gas measurement reveals the following: pH 7.24, PaCO2 58, PaO2 100, and HCO3 - 28. Which of the following is the most appropriate initial therapy for this patient?

Thoracic epidural narcotics have become an increasingly popular means of postoperative pain relief in thoracic and upper abdominal surgery. Local action on g-opiate receptors ensures pain relief and consequent improvement in respiration without vasodilation or paralysis. The less lipid-soluble opiates are effective for long periods. Their slow absorption into the circulation also ensures a low incidence of centrally mediated side effects, such as respiratory depression or generalized itching. When these do occur, the intravenous injection of an opiate antagonist is an effective antidote. The locally mediated analgesia is not affected. One poorly understood side effect, which is apparently unrelated to systemic levels, is a profound reduction in gastric activity. This may be an impoant consideration after thoracic surgery when an early resumption of oral intake is anticipated.