An Evaluation of a Single Dose of Magnesium to Supplement Analgesia After Ambulatory Surgery: A Randomized Controlled Trial

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An Evaluation of a Single Dose of Magnesium to Supplement Analgesia After Ambulatory Surgery: A Randomized Controlled Trial
Martin R. Tramèr,* Chris J. Glynn†
(Anesth Analg, 104:1374-1379, 2007)
*Division of Anesthesiology, Departments of Anesthesiology, Pharmacology, and Intensive Care, University Hospitals Geneva, Geneva, Switzerland; and †Pain Relief Unit, Nuffield Department of Anesthetics, The Churchill, Oxford, United Kingdom
Magnesium may be a useful adjuvant to postoperative analgesia, based on previous studies. Two hundred patients undergoing ambulatory ilioinguinal hernia repair or varicose vein surgery under general anesthesia (propofol, fentanyl, isoflurane-N2O) were randomized (101 magnesium, 99 placebo) to receive magnesium sulfate 4 grams intravenously or physiological saline after induction. Preoperatively, all patients received diclofenac 100 mg rectally, and those undergoing hernia repair had a postoperative ilioinguinal-iliohypogastric nerve block performed. Pain, analgesia consumption, and adverse effects were recorded in the recovery room and, using a questionnaire, up to 3 days postoperatively. No differences existed in hemodynamic variables before and immediately after injection of the study drug. Intensity of pain at rest and on movement after 1, 2, and 4 hours, time to first rescue analgesic, and cumulative numbers of nonopioid and opioid analgesics were similar among groups. Likewise, there was no difference in the incidence of postoperative nausea and vomiting, dizziness, headache, or fainting. The incidence of postoperative shivering was markedly lower in the magnesium group (4% vs 13.1%). Adequately completed questionnaires were returned by 84 placebo and 82 magnesium patients. No difference existed between groups for any of the outcomes analyzed during the first 3 postoperative days, neither for patients undergoing inguinal hernia repair nor for those undergoing varicose vein stripping. In patients undergoing ambulatory ilioinguinal hernia repair or varicose vein surgery under general anesthesia supplemented with other analgesic adjuvants, pretreatment with magnesium sulfate 4 g has no effect on postoperative pain and analgesic consumption.
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