Effects of the extradural administration of morphine, or bupivacaine, on the endocrine response to upper abdominal surgery

Abstract

The endocrine response, and the relief of pain, following the extradural administration of morphine or a local anaesthetic agent bupivacaine (0.5%) were studied for 24h after abdominal surgery and compared with a control group given conventional i.v. morphine after operation. Samples were taken before and at 2, 4, 6, 12 and 24 h after skin incision. Pain relief in both extradural groups was significantly better when compared with the control group. In all three groups, the plasma concentration of cortisol was increased immediately after surgery. Thereafter, significantly lower values were seen in the extradural groups. Plasma adrenaline concentration was lower immediately after surgery only in the group given the extradural local anaesthetic. Plasma noradrenaline concentration remained unchanged after extradural local anaesthesia while an intermediate increase occurred after extradural morphine. Plasma noradrenaline concentration was significantly greater in the controls compared with both extradural groups. Our results indicate that extradural analgesia with a local anaesthetic drug can suppress the increases in the plasma concentrations of the catecholamines and cortisol after surgery. In contrast to extradural local anaesthetic extradural morphine cannot suppress the endocrine response immediately after surgery. However, later in the postoperative period, extradural morphine can suppress the endocrine response, thus indicating that postoperative pain is a factor involved in the stress response following surgery.