[Effect of continuous epidural infusion of morphine for postoperative analgesia on pituitary-adrenocortical function]

Plasma levels of cortisol, ACTH and beta-endorphin like immunoreactivity (beta-ELI) were measured to evaluate postoperative pain relief with epidural morphine and systemic analgesics in conjunction with endocrine functions in 16 patients who underwent gastrectomy. Eight of these patients (epidural morphine group) obtained postoperative analgesia with continuous epidural infusion of morphine with a pump as in our previous report. A bolus of epidural morphine was administered through an indwelling thoracic (Th8,9) catheter at 3 hrs prior to the proposed end of the surgery, which was followed with continuous epidural infusion of morphine at a rate of 0.167-0.042 mg.hr-1 with a pump (CADD-PCA, Model 5200P, Pharmacia) during and after anesthesia and surgery with gradual decrease in dose until the third postoperative day. The remaining eight patients (systemic analgesics group) repeatedly received systemic pentazocine and buprenorphine when needed. Plasma cortisol levels increased significantly at the end of surgery and after in both groups. However plasma concentrations of cortisol in the epidural morphine group were significantly lower than those in the systemic analgesics group on the first and second postoperative days. Plasma levels of ACTH and beta-ELI increased significantly at the end of surgery but returned to levels of the previous day in both groups postoperatively. Our study suggests that continuous epidural infusion of morphine is adequate for postoperative pain relief and has suppressing effect on plasma cortisol levels as compared with systemic analgesics regimen.