Magnesium Sulfate for Reducing Postoperative Shivering Incidence

Abstract

Introduction: Postoperative shivering is a common distressing complication after general anesthesia, increasing metabolic demand and intracranial pressure. This review evaluates the prophylactic efficacy of intravenous magnesium sulfate compared to other pharmacologic agents.

Methods: A literature review included randomized placebo-controlled trials of adult patients undergoing surgery under general anesthesia. Magnesium sulfate was administered intraoperatively before emergence. The primary outcome was shivering incidence graded by the Wrench scale. Secondary outcomes included core temperature changes and adverse events.

Results: Twenty trials (1,856 patients) were analyzed. Magnesium sulfate reduced shivering incidence by 47% compared to placebo, with a number needed to treat of five. Efficacy was comparable to meperidine and tramadol but inferior to clonidine. Hypothermia on arrival to post-anesthesia care unit did not differ between groups. Mild hypotension and flushing were more common with magnesium.

Discussion: Magnesium suppresses shivering by antagonizing N-methyl-D-aspartate receptors, inhibiting calcium influx into smooth muscle, and reducing norepinephrine release. The lack of effect on core temperature indicates that magnesium likely raises the shivering threshold rather than altering heat balance. Most trials used a fixed magnesium dose rather than weight-based, potentially underdosing larger patients.

Conclusions: Intravenous magnesium sulfate effectively reduces postoperative shivering with a favorable safety profile. A weight-based dose of 30 mg/kg is recommended given 15 to 30 minutes before emergence.