Influence of Epidural Morphine on Postoperative Pain, Endocrine-Metabolic, and Renal Responses to Surgery. A Controlled Study

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Abstract
In order to assess the analgesic properties of epidural low‐dose morphine and its possible influence on thr adrenocortical, hyperglycemic, renal, electrolyte and leukocyte responses to surgery and nitrogen excretion, a double‐blind randomized study was undertaken in 14 otherwise healthy patients admitted lor hysterectomy under halothane, N2O/O2 anesthesia. Before induction of anesthesia, an epidural catheter was introduced into the lumbar epidural space. After induction of anesthesia, either morphine 4 mg in 10 ml saline or 10 ml saline was injected into the epidural space, according to the allocation. Postoperatively, the degree of pain was evaluated by means of a visual analogue scale (0–10). When pain score exceeded 5 points during the 24‐h trial, either 4 mg morphine in saline or saline was given epidurally. If the pain score did not decrease more than 2 points after an epidural injection, morphine was given parenterally (5 mg i.v. f 5 mg i.m.). The results showed that pain scores, duration of pain relief and doses of morphine differed significantly between groups (P<0.05). Plasma concentrations of cortisol and glucose, plasma‐ and urine electrolytes, 24‐h creatinine and free‐water clearances, diuresis, fluid balance, leukocyte count and nitrogen excretion differed insignificantly between groups. In conclusion, epidural low‐dose morphine is a superior alternative to conventional postoperative pain treatment because of greater and longer lasting pain relief, without apparent side‐effects. The measured endocrine‐metabolic and renal responses did not differ between groups, indicating that low‐dose epidural morphine does not inhibit afferent neurogenic stimuli from the site of surgical trauma.