Effect of Epidural Morphine on Minimum Alveolar Concentration of Isoflurane in Humans

BACKGROUND AND AIMS: The anaesthetic potency of volatile anaesthetic agents is measured by the minimum alveolar concentration (MAC) required to suppress response in 50% of subjects. We studied the effect of epidural morphine on MAC of isoflurane in humans. SETTINGS AND DESIGN: A prospective single-blind study designed to study the effect of epidural morphine on MAC of isoflurane. SUBJECTS AND METHODS: Forty-eight patients were randomly divided into two groups - Group I patients received 3 mg morphine in 10 ml saline, and Group II patients received 10 ml saline epidurally. Anaesthesia was induced with isoflurane in oxygen and nitrous oxide. Later nitrous oxide was discontinued and MAC of isoflurane determined using modified Dixon's method of sequential sampling. RESULTS: Epidural morphine resulted in a significant reduction in MAC of isoflurane, 0.98 vs. 1.14 in control group (p<0.05). CONCLUSIONS: Epidural administration of 3 mg morphine in 10 ml saline decreased the MAC of isoflurane.