Variable Versus Fixed-rate Infusion of Phenylephrine During Cesarean Delivery

A Randomized Controlled Trial

Ahmed Hasanin; Sara Habib; Yaser Abdelwahab; Mohamed Elsayad; Maha Mostafa; Marwa Zayed; Mohamed Maher Kamel; Kareem Hussein; Sherin Refaat; Ahmed Y. Fouda; Ahmed A. Wali; Khaled A. Elshafaei; Doaa Mahmoud; Sarah Amin


BMC Anesthesiol. 2019;19(197) 

In This Article

Abstract and Introduction


Background: Phenylephrine is the most commonly used vasopressor for prophylaxis against maternal hypotension during cesarean delivery; however, the best regimen for its administration is not well established. Although variable infusion protocols had been suggested for phenylephrine infusion, evidence-based evaluation of variable infusion regimens are lacking. The aim of this work is to compare variable infusion, fixed on-and-off infusion, and intermittent boluses of phenylephrine for prophylaxis against maternal hypotension during cesarean delivery.

Methods: A randomized controlled study was conducted, including full-term pregnant women scheduled for elective cesarean delivery. Participants were divided into three groups which received phenylephrine by either intermittent boluses (1.5 mcg/Kg phenylephrine), fixed on-and-off infusion (with a dose of 0.75 mcg/Kg/min), or variable infusion (with a starting dose of 0.75 mcg/Kg/min). The three groups were compared with regard to frequency of: maternal hypotension (primary outcome), second episode hypotension, reactive hypertension, and bradycardia. Other outcomes included heart rate, systolic blood pressure, physician interventions, and neonatal outcomes.

Results: Two-hundred and seventeen mothers were available for final analysis. The 2 infusion groups showed less incidence of maternal hypotension {26/70 (37%), 22/71 (31%), and (51/76 (67%)} and higher incidence of reactive hypertension compared to the intermittent boluses group without significant differences between the two former groups. The number of physician interventions was highest in the variable infusion group compared to the other two groups. The intermittent boluses group showed lower systolic blood pressure and higher heart rate compared to the two infusion groups; whilst the two later groups were comparable.

Conclusion: Both phenylephrine infusion regimens equally prevented maternal hypotension during cesarean delivery compared to intermittent boluses regimen. Due to higher number of physician interventions in the variable infusion regimen, the current recommendations which favor this regimen over fixed infusion regimen might need re-evaluation.


Subarachnoid block is the preferred route of anesthesia during cesarean delivery. Maternal hypotension is a frequent and deleterious complication after subarachnoid block in this population. Without prophylactic vasopressors, the post-spinal hypotension affects nearly 60% of mothers undergoing cesarean delivery.[1,2] Using vasopressors for prophylaxis against maternal hypotension have become fundamental in modern anesthetic practice.[3,4]

Phenylephrine (PE) is still the most commonly used vasopressor during cesarean delivery;[3,4] however, the most appropriate protocol for PE administration is still unknown. PE is usually administered as single shot,[5] fixed (on-off) rate infusion,[6] or variable rate infusion.[7] The objective of all protocols is to achieve the least possible incidence of maternal hypotension, and avoiding reactive hypertension, with the least number of physician interventions. Continuous infusion regimens of PE are suggested to provide less incidence of hypotension compared to single bolus; however, stable hemodynamic profile requires a balance between preventing hypotension and avoiding unnecessary hypertension. Thus, reaching a definitive ideal regimen should be based upon this balance. To the best of our knowledge, no studies had previously compared variable rate and fixed (on-off) rate protocols for PE infusion during cesarean delivery. In this study, we compared variable infusion rate (at a starting rate of 0.75 mcg/Kg/min), fixed (on-off) rate (0.75 mcg/Kg/min), and intermittent boluses regimen (1.5 mcg/Kg) for prophylaxis against maternal hypotension during cesarean delivery.