Effect of phenylephrine infusion on postpartum blood loss after cesarean delivery: A Placebo-controlled, randomized clinical trial

Background: Preclinical studies have documented the role of alpha-adrenergic agonists in myometrial contraction. Phenylephrine is frequently used to prevent and treat post-spinal hypotension during cesarean delivery. We hypothesized phenylephrine would reduce postpartum blood loss due to alpha-1 receptor-mediated uterine and vascular smooth muscle contraction.

Objectives: This translational study aimed to evaluate the role of phenylephrine in reducing postpartum blood loss due to alpha-1 receptor mediated uterine and vascular smooth muscle contraction.

Methods: This was a prospective, randomized, placebo-controlled, blinded, pilot, clinical trial. Low-risk parturients undergoing cesarean delivery under spinal anaesthesia were recruited in this study. The women were randomized to receive phenylephrine or placebo (normal saline) infusion. Each ml of phenylephrine contained 60 micrograms. The study drug began simultaneously with the start of spinal anesthesia, and was stopped at the end of surgery. The infusion rate was started at 50 mcg/min and was titrated to maintain the systolic blood pressure between 80-120 % of baseline. The primary outcome measure was postpartum blood loss till 24 hours postpartum, and it was assessed using a surgical swab weighing technique added to suction canister blood contents. The secondary outcomes were incidence of hypertension, hypotension, Apgar score, cord blood gas analysis and neonatal intensive care unit admission (NICU) admission.

Results: One hundred six women received study drugs and were eligible for final analysis. The demographic data, obstetric profiles and medications were comparable. In the phenylephrine group, the mean postpartum blood loss {median (interquartile range)} was significantly lower {(420 (349-502) vs 494 (397-600) ml; p= 0.009)}. Additionally, a significantly lower number of women had > 500 ml of blood loss in the phenylephrine group (26.4% vs 47.1%; p=0.02). Furthermore, more women in the control arm needed blood transfusion (37.7% vs 16.9%; p=0.01). Six women each had bradycardia and hypertension in the phenylephrine group. NICU admission, Apgar score, and umbilical artery PH were comparable.

Conclusion: Continuous phenylephrine infusion led to a statistically significant but clinically inconsequential reduction in postpartum blood loss in low-risk parturients undergoing cesarean delivery under spinal anesthesia.