Effect of interpleural morphine on postoperative pain and pulmonary function after thoracotomy

We have investigated the effect of interpleural morphine on postoperative pain and pulmonary function after thoracotomy. At the end of surgery, an interpleural catheter was inserted in 17 patients and, in a double-blind and randomized manner, either a bolus of morphine 2.5 mg interpleurally (i.p.) and normal saline i.v. (group I) or, as a control for systemic absorption, morphine 2.5 mg i.v. and i.p. saline (group II) was injected. After the initial bolus, a continuous infusion of morphine 0.5 mg h-1 i.p. and saline i.v. (group I) or morphine 0.5 mg i.v. and saline i.p. (group II) was maintained for 24 h. Postoperative pain was assessed by a visual analogue scale, a numerical rating scale and the McGill Pain Questionnaire. Pulmonary function was assessed by spirometry. Supplementary analgesics, side effects, degree of sedation, vital signs and chest tube drainage were recorded. All variables were assessed on the day before surgery and 1, 2, 3, 4, 5, 6 and 24 h and 7 days after surgery. Supplementary morphine was given upon request. There was no significant difference in any pain measure or postoperative pulmonary function variable between the groups. We conclude that, after thoracotomy, interpleural morphine does not provide superior analgesia or improve pulmonary function compared with systemic morphine.