[Epidural anesthesia and metabolic response to surgical stress]

Surgical stress leads to reproducible physiological metabolic and hormonal responses, characterized by on altered carbohydrate metabolism, a net loss of protein and an increased lipolysis. They are due to an increased secretion of catecholamines, ACTH, cortisol and cytokines. Epidural analgesia prevents the hyperglycaemic, cortisol and adrenocortical responses to surgery. The lipolysis and the loss of protein are also attenuated. This effect only occurs in lower abdominal surgery, with an epidural blockade extending from T4 to S5, carried out with local anesthetic agents and started before the skin incision. However, such a blockade abates, but does not suppress, the metabolic response to upper abdominal or thoracic surgery, probably because of persistent vagal afferences, the incomplete blockade of somatic afferents, and a stimulation of the diaphragm and peritoneal free nerve endings. Likewise, epidural morphine does not modify the intraoperative metabolic and hormonal responses. The main reason is most probably the failure of opioids to block the sympathetic system, as well as their insignificant effects on fast conducting fibers.