Key result
Magnesium sulfate dosed by actual body weight significantly reduced postoperative pain scores compared to control (p<0.001) and dosing by adjusted ideal body weight (p=0.017) in obese patients.
Why the study?
Although magnesium sulfate reduces opioid use and associated side effects, no consensus exists on whether optimal dosing in obese patients should be based on actual body weight or adjusted ideal body weight.
Does magnesium sulfate infusion calculated by actual body weight improve postoperative analgesia compared to adjusted ideal body weight in obese patients undergoing general anesthesia?
RCT (n=75)
Double-blind
randomized
Does magnesium sulfate infusion calculated by actual body weight improve postoperative analgesia compared to adjusted ideal body weight in obese patients undergoing general anesthesia?
Calculating the dose of magnesium sulfate based on actual body weight enhances postoperative analgesia in obese patients compared to using adjusted ideal body weight.
Actual body weight dosing improves postoperative analgesia versus adjusted ideal body weight in obese patients; extends magnesium dosing evidence from RCTs.
Background: Magnesium sulfate reduces opioid use and its associated side effects. However, no consensus exists on whether the optimal dosing should be based on actual body weight or adjusted ideal body weight. The primary objective of this study was to compare postoperative analgesia after magnesium sulfate infusion, using doses calculated based on actual body weight versus adjusted ideal body weight. Methods: This prospective, randomized, double‐blind, controlled clinical trial included 75 participants who underwent target‐controlled intravenous general anesthesia. The participants were divided into three groups: a control group (CG), a group receiving magnesium sulfate calculated by actual body weight (AWG), and a group receiving magnesium sulfate calculated based on the adjusted ideal body weight (IWG). Results: The AWG had significantly lower pain scores than the CG ( p < 0.001) and IWG ( p = 0.017). Opioid use was similar between the AWG and IWG, but significantly higher in the CG (AWG = IWG, p = 0.08; CG > AWG, p < 0.001; CG = IWG, p 0.03). The increase in magnesium concentration did not reach clinically relevant levels. Neuromuscular blockade latency decreased in the groups receiving magnesium sulfate ( p < 0.001 in both comparisons) compared to the CG. Conclusion: Calculating the dose of magnesium sulfate based on actual body weight enhances postoperative analgesia. The increase in magnesium concentration was not clinically significant and did not interfere with the action of cisatracurium in the groups receiving magnesium sulfate. Trial Registration: ClinicalTrials.gov identifier: NCT04645719
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Filho et al. (2025) conducted an RCT in Obesity requiring general anesthesia (n=75). Magnesium sulfate infusion vs. Control group and magnesium sulfate calculated based on adjusted ideal body weight was evaluated on Postoperative analgesia (pain scores) (p=< 0.001). Magnesium sulfate dosed by actual body weight significantly reduced postoperative pain scores compared to control (p<0.001) and dosing by adjusted ideal body weight (p=0.017) in obese patients.
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