Association of a single low-dose intraoperative magnesium bolus with postoperative opioid requirements: a multicentre...

Few studies have investigated the effects of a low-dose, single magnesium bolus on postoperative pain. We sought to evaluate the association between an intraoperative bolus of 2 g magnesium iv and postoperative opioid consumption, with secondary outcomes focused on potential adverse effects.

We conducted a multicentre retrospective cohort study of adult patients from 14 hospitals in the northeastern USA who had received general anesthesia for elective surgery between 1 January 2018 and 31 December 2022. The primary outcome was total postoperative opioid consumption, defined as intravenous morphine milligram equivalents (IV MME) administered during the postanesthesia care unit (PACU) period. Secondary outcomes included PACU recovery time, levels of consciousness in the PACU, and intraoperative hemodynamics.

Among 257,206 patient encounters meeting inclusion criteria, 16,233 (6%) received a magnesium bolus. Of those, 95% were given a dose of 2 g iv. In adjusted models, magnesium was associated with increased postoperative opioid consumption (mean difference, 0.9 IV MME; 95% confidence interval [CI], 0.8 to 1.0; P < 0.001). No difference was observed in levels of consciousness in the PACU or in PACU recovery times. After magnesium administration, arterial blood pressure and heart rate decreased, with a gradual return to baseline and with small estimated absolute changes.

Intraoperative administration of a single bolus of 2 g magnesium iv was associated with a negligible change in postoperative opioid consumption and trivial hemodynamic effects. The results of this study suggest that a single low-dose magnesium bolus may offer no clinical benefit.