Magnesium Sulfate, Nicardipine, and Volatile Anesthetics in Severe Preeclampsia: Clinical and Mechanistic Implications for Uterine Atony and Postpartum Hemorrhage

Severe preeclampsia frequently requires the concurrent administration of magnesium sulfate, intravenous nicardipine, and volatile anesthetics during the peri-delivery period, exposing the myometrium to convergent inhibition of calcium-dependent contraction. We conducted a narrative review guided by the Scale for the Assessment of Narrative Review Articles framework. We searched PubMed/MEDLINE and screened reference lists through March 2026, prioritizing mechanistic studies, human myometrial experiments, clinical cohorts, randomized trials, meta-analyses, and contemporary obstetric anesthesia guidance. The evidence indicates that convergence occurs at multiple levels of the excitation-contraction coupling machinery, including L-type calcium channel influx, inositol 1,4,5-trisphosphate-mediated intracellular calcium release, oxytocin receptor signaling, intercellular coupling through connexin-43 gap junctions, and calcium sensitization via the Ras homolog family member A (RhoA)/Rho-kinase pathway. Magnesium sulfate acts as a broad calcium antagonist, nicardipine blocks L-type calcium channels, and volatile anesthetics depress spontaneous and oxytocin-induced force generation. Clinical evidence is more heterogeneous: magnesium sulfate shows mixed hemorrhagic associations, direct postpartum hemorrhage data for nicardipine remain sparse, and general anesthesia is associated with greater hemorrhagic risk than neuraxial techniques. This “tocolytic triad” is therefore best viewed as a mechanistically grounded risk model rather than a validated clinical syndrome. We propose a graded exposure-burden care bundle, anchored in quantified blood loss assessment, to align hemorrhage preparedness with cumulative pharmacologic inhibition of postpartum uterine contraction.