Vasopressor Regimens and Maternal Core Temperature During Cesarean Delivery: A Randomized, Double‑blind, Non‑inferiority Trial

Background: Norepinephrine (NE), a vasopressor commonly used during cesarean section, avoids the phenylephrine (PE)-induced decreases in heart rate and cardiac output. Conversely, PE reduces the incidence and severity of maternal shivering and hypothermia during cesarean section. Therefore, before recommending NE as a complete replacement for PE, their effects on maternal core temperature must be compared. This study aimed to determine whether prophylactic infusion of NE is non-inferior to PE in maintaining maternal core temperature. Materials and Methods: One hundred and forty eligible women scheduled for cesarean section under spinal or combined spinal-epidural anaesthesia were randomly assigned to either the NE or PE group. All participants, caregivers, and outcome assessors were blinded. NE (8 μg/mL) or PE (100 μg/mL) was administered intravenously at a fixed rate of 15 mL/h (equivalent to NE 2 μg/min or PE 25 μg/min), starting concurrently with the subarachnoid injection, and continuing until the end of surgery. The primary outcome was postoperative maternal core temperature, with a non-inferiority margin set at 0.2°C. Results: Postoperative maternal core temperature was non-inferior in the NE group (mean, 36.35°C; 95% confidence interval [CI], 36.28– 36.42) compared to the PE group (mean, 36.41°C; 95% CI, 36.34– 36.49). The mean difference between the two groups was − 0.06°C (95% CI, - 0.16 to 0.04), meeting the criterion for non-inferiority (one-sided p = 0.008). The incidence of bradycardia was significantly lower in the NE group than in the PE group (7.4% vs. 33.8%; p < 0.001). No significant differences were found between the groups in the incidence or severity of shivering, the incidence of hypothermia, or the thermal comfort score. Conclusion: NE was not inferior to PE regarding its effect on maternal core temperature, providing a rationale for its use during cesarean sections.