A dose-response study of nalbuphine for post-thoracotomy epidural analgesia.

The analgesic efficacy and side-effects of epidural nalbuphine (0.075-0.3 mg.kg-1) were compared with epidural morphine 0.1 mg.kg-1 in a randomised double-blind study in post-thoracotomy patients. The drugs were administered via a lumbar epidural catheter one hour before the end of surgery. Efficacy was assessed using visual analogue pain scores and supplementary iv fentanyl requirements; respiratory function was studied with an inductive plethysmograph and arterial blood gas analysis; and plasma nalbuphine levels were measured. Pain scores and fentanyl supplementation were lowest in the morphine group (P less than 0.01). No dose-response effect was apparent in the nalbuphine dose-range studied. Respiratory depression was more common in patients receiving morphine (higher mean PaCO2P less than 0.01, more frequent apnoeas greater than 15 sec P less than 0.05, and incidence of PaCO2 greater than 50 mmHg requiring naloxone P less than 0.01). There were no differences in haemodynamic variables, sedation, or other side-effects among the groups. The pharmacokinetic profile of epidural nalbuphine was similar to that seen with rapid iv injection. The results indicate that, relative to morphine, lumbar epidural nalbuphine is an ineffective analgesic after thoracotomy. Despite the lower incidence of respiratory depression its administration by this route cannot be recommended.