Dose-response relationship of prophylactic norepinephrine infusion for prevention of spinal anesthesia-induced hypotension during caesarean delivery: A comparative study of normal weight and obese parturients.

Obese parturients are at increased risk of spinal anesthesia-induced hypotension during cesarean delivery, but optimal prophylactic norepinephrine dosing remains unclear. In this randomized, double-blind, dose-response study, 200 parturients undergoing elective cesarean delivery were stratified into obese (BMI ≥30 kg/m²) and normal weight (BMI 18.5-24.9 kg/m²) groups. Within each group, patients received norepinephrine infusion at 0.02-0.06 µg·kg⁻¹·min⁻¹. Standardized combined spinal-epidural anesthesia with 16 mg hyperbaric ropivacaine was used, and infusion was started immediately after spinal injection. Hypotension was defined as SBP <90 mmHg or >20% decrease from baseline, and success as absence of hypotension. Probit regression was used to estimate ED50 and ED95. ED50 and ED95 were 0.022 (95% CI 0.015-0.029) and 0.051 (0.041-0.061) µg·kg⁻¹·min⁻¹ in normal weight, compared with 0.036 (0.029-0.043) and 0.080 (0.058-0.102) µg·kg⁻¹·min⁻¹ in obese parturients. The relative potency ratio was 1.597 (95% CI 1.007-2.187; P=0.013). Neonatal outcomes and maternal adverse effects were comparable. Obese parturients require higher weight-adjusted norepinephrine infusion rates to prevent spinal anesthesia-induced hypotension during cesarean delivery.