A Dose-Response Study of Four Fixed Weight-Based Phenylephrine Dosages in Obese Cesarean Delivery Patients to Prevent Spinal Anesthesia-Induced Hypotension.

Background and objective: Reports have suggested the use of intravenous infusion of vasopressors as an approach to prevent spinal anesthesia-induced hypotension (SAIH) in women undergoing cesarean deliveries. However, data on the suitability of this technique for obese people are limited. As such, the current experiment was designed to clarify the dose-response relationship associated with the preventive administration of phenylephrine to avoid SAIH during cesarean delivery in obese parturients under combined spinal-epidural anesthesia.

Methods: The current study included 100 parturients with a body mass index ≥30 kg/m² who were undergoing cesarean section delivery. They were randomly treated with phenylephrine at different doses: 0.375, 0.5, 0.625, or 0.75 μg/kg/min. An infusion of phenylephrine was deemed beneficial if hypotension was absent, with hypotension defined as a systolic blood pressure <90 mmHg or <80% of the baseline value between spinal injection and the delivery of the newborn. The 50% and 90% effective doses (ED₅₀ and ED₉₀, respectively) for prophylactic phenylephrine were determined via a probit regression.

Results: Respective rates of hypotension in the 0.375, 0.5, 0.625, and 0.75 groups were 52% (13/25), 40% (10/25), 20% (5/25), and 0% (0/25). ED₅₀ and ED₉₀ values of 0.42 (95% confidence interval 0.30-0.48) and 0.68 (95% confidence interval 0.60-0.87) μg/kg/min were calculated for phenylephrine treatment.

Conclusion: The study results indicated that prophylactic phenylephrine, which prevents SAIH in obese parturients following cesarean delivery, has calculated values of 0.42 and 0.68 μg/kg/min. These findings may contribute to developing appropriate clinical practice guidelines for improved patient management.

Clinical trial registration: https://www.chictr.org.cn/bin/project/edit?pid=153050 . Identifier ChiCTR2200058125.