Comparison of Intramuscular and Epidural Morphine for Postoperative Analgesia in the Grossly Obese

Abstract

In a randomized double-blind study of thirty grossly obese patients undergoing gastroplasty for weight reduction, the effects of intramuscular and epidural morphine were compared as regards analgesia, ambulation, gastrointestinal motility, early and late pulmonary function, duration of hospitalization, and occurrence of deep vein thrombosis in the postoperative period. The patients were operated on under thoracic epidural block combined with light endotracheal anesthesia. A six-grade scale was devised to quantify postoperative mobilization. A radioactive isotope method using 99mTc -plasmin was employed to detect postoperative deep vein thrombosis. For 14 hr after the first analgesic injection, respiratory frequency was noted every 15 min and arterial blood gases were measured hourly. Peak expiratory flow was recorded daily until the patient was discharged from hospital. Spirometry was performed the day before and the day after surgery. Plasma concentrations of morphine were measured after both intramuscular and epidural administration. Both intramuscular and epidural morphine gave effective analgesia, but the average dose of intramuscular morphine was up to seven times greater than that required by the epidural route. A larger number of patients receiving epidural morphine postoperatively were able to sit, stand, or walk unassisted within 6, 12, and 24 hr, respectively. Being alert and more mobile as a result of superior postoperative analgesia from epidural morphine, patients in this group benefited more from vigorous physiotherapy routine, which resulted in fewer pulmonary complications. Furthermore, earlier postoperative recovery of peak expiratory flow and bowel function presumably contributed to a significantly shorter hospitalization in patients receiving epidural morphine. There was no evidence of prolonged respiratory depression in this high-risk category of patients. The 99mTc -plasmin tests revealed no significant difference between the two groups.