The effect of preoperative single dose magnesium sulphate on the postoperative morphine consumption: a preliminary study

Abstract

Magnesium is a NMDA receptor antagonist. NMDA receptor antagonists potentiate the analgesic effects of opioids. The aim of this preliminary, randomised, double blind, placebo controlled study was to evaluate the effect of a preoperative single dose magnesium sulphate on the postoperative morphine consumption. At the preoperative period either 40 mg/kg magnesium sulphate (GI) or % 0.9 NaCl (GII) were given to 30 patients who underwent gynecological surgery. Serum magnesium levels were measured preoperatively, after induction and after extubation. After standardized anaesthesia method postoperative analgesia was provided by the patient controlled analgesia (PCA) method using morphine. The groups were compared for the total morphine consumption, PCA demand and delivery rates, satisfaction of the patient and side effects. Magnesium levels were higher in GI than GII after induction and extubation. The total morphine consumption in 24 hours and patient demand rates were statistically significantly lower in GI than in GII (24.5±5.5 / 28.1±3 mg/day and 68.8±17.8 / 84.7±20.7 respectively; p=0.04). Patient satisfaction was better in GI. No differences between the two groups were detected in terms of side effects. We conclude that 40 mg/kg magnesium sulphate as a single preoperative dose reduces postoperative morphine requirement without side effects and increases the postoperative patient comfort.