Magnesium administration for vasospasm prevention in acute aneurysmal SAH: a multicenter randomized controlled trial.

Aneurysmal subarachnoid hemorrhage (aSAH) is associated with significant morbidity and mortality, with cerebral vasospasm (CV) and delayed cerebral ischemia (DCI) being the primary contributors to poor outcomes. Magnesium sulfate (MgSO₄) has demonstrated neuroprotective and vasodilatory properties in preclinical models. This study aimed to evaluate the effect of targeted serum magnesium (Mg) maintenance on CV and exploratory clinical outcomes following aSAH. We conducted a prospective, multicenter, single-blind RCT across four neurocritical care units in Korea between 2019 and 2024. A total of 121 aSAH patients were randomized to receive either IV MgSO₄or placebo within six hours of admission. Mg was infused to maintain serum concentrations between 2.0 and 3.0 mg/dL for 14 days. The primary outcome was incidence of CV assessed by transcranial doppler. Secondary outcomes included DCI, ICU and hospital length of stay, modified rankin scale (mRS) at 30 days. There was no significant difference in overall CV incidence; however, the Mg group demonstrated significantly lower mean flow velocity and Lindegaard ratio on days 4-9, indicating reduced vasospasm severity. In exploratory multivariable analyses, a median serum Mg concentration > 2.5 mg/dL during the first 14 hospital days was independently associated with lower risks of CV and DCI. No significant differences were found in mRS scores, ICU and hospital stay, or serious adverse events between groups. Early targeted Mg administration improved TCD-derived hemodynamic markers during the peak vasospasm window; however, it did not significantly reduce CV incidence, DCI, ICU or hospital stay, or 30-day functional outcome.