Effects of epidural administration of local anaesthetics or morphine on postoperative nitrogen loss and catabolic hormones

Abstract

To examine the effects of postoperative epidural analgesia with local anaesthetics or morphine on the excess nitrogen loss after upper abdominal surgery and to assess the roles of catabolic hormones in the nitrogen loss, urinary excretion of nitrogen and catecholamines and plasma concentrations of cortisol and glucagon were measured in three groups of patients undergoing elective gastrectomy. Group G patients received the operation under general anaesthesia, and their postoperative pain was relieved by intermittent injections of analgesics. Group PE received prolonged epidural analgesia with local anaesthetics during and after surgery. Group EM received epidural analgesia intra-operatively and epidural morphine postoperatively. Urinary nitrogen excretion during the first three postoperative days was significantly less in the PE and EM groups than in the G group, and the PE group excreted slightly less nitrogen than the EM group. In the G group, urinary excretion of adrenaline increased mainly on the day of operation, and noradrenaline chiefly on postoperative days. These catecholamine responses were almost completely abolished in the PE group, and significantly inhibited in the EM group. Plasma cortisol response was most remarkable shortly after the operation and then decreased in all groups, but was significantly lower in the two epidural groups than in the G group throughout the study. Plasma glucagon increased postoperatively in all groups, and the increase was less pronounced in both epidural groups than in the G group. These results suggested that an elevated sympathic activity, represented by increased noradrenaline excretion and elicited by painful nociceptive and sympathetic nervous afferents, is responsible for the postoperative nitrogen loss which is mediated by glucagon and cortisol.