PERIOPERATIVE MAGNESIUM INFUSION AND POSTOPERATIVE PAIN

Background: NMDA receptor activation is considered one of the mechanis ms involved in postoperative pain and hypersensitivity. Magnesium is t he physiological blocker of the NMDA-receptor-complex-associated calci um ionophore. The aim of this study was to determine if a pre-, intra- and postoperative infusion of magnesium would reduce postoperative pa in. Methods: In a prospective, randomised, double-blinded and placebo- controlled study 24 patients undergoing elective hysterectomy in stand ardised general anaesthesia received a 5 h infusion of either placebo or magnesium laevulinate (initial bolus 8 mmol: then 8 mmol/h) startin g with induction of anaesthesia. Postoperative analgesia was by PCA mo rphine for the first 48 h and patients were followed for 5 d with regu lar assessments of pain and side-effect scores. Results: Overall, pain scores were similar with magnesium and placebo infusion, although pat ients in the magnesium group experienced more episodes of severe or un bearable pain (placebo=6%, magnesium=16%, P=0.02). Median pain scores were higher in the magnesium group only at 3 h postoperatively (P=0.04 ): afterwards there were no significant differences. Except for the fi rst postoperative hour (placebo=12.8+/-4.7 mg, magnesium=9.3+/-3.2 mg, P=0.04), cumulative morphine consumption was similar. Gastrointestina l complication rates and patient satisfaction were similar in both gro ups. Conclusions: Perioperative magnesium infusion does not improve po stoperative analgesia. At the doses used in this study, the use of mag nesium is associated with short-term decreases in postoperative analge sia.