A randomized control trial comparing weight adjusted dose versus fixed dose prophylactic phenylephrine infusion on maintaining systolic blood pressure during caeserean section under spinal anaesthesia

Date of Award


Document Type


Degree Name

Master of Medicine (MMed)


Anaesthesiology (East Africa)


Background: Spinal anaesthesia is the standard of care for elective caesarean delivery. Its advantages over general anaesthesia include: decreased blood loss, reduced postoperative pain and faster recovery time. Despite these advantages, the sympathetic blockade induced by spinal anaesthesia results in 80 percent incidence of hypotension without prophylactic management. This hypotension can cause: nausea, vomiting, cardiovascular collapse or even loss of consciousness in the mother, and fetal acidosis.

Current evidence supports co-loading with intravenous fluids in conjunction with the use of vasopressors as the most effective way to prevent and treat the hypotension. Phenylephrine is the accepted vasopressor of choice in the parturient.

A prophylactic phenylephrine infusion combined with a fluid co-load is proven to be an effective and safe method of maintaining maternal hemodynamic stability. While most published studies have assessed the effectiveness of a prophylactic phenylephrine fixed dose infusion, no published study has assessed the effect of a prophylactic phenylephrine weight adjusted dose infusion on maintaining maternal hemodynamic stability following spinal anesthesia for cesarean delivery.

Objective: Compare the incidence of hypotension between women undergoing elective caesarean section under spinal anaesthesia, assigned to receive prophylactic phenylephrine infusion at a fixed dose of 37.5 micrograms per minute versus a weight adjusted dose of 0.5 micrograms per kilogram per minute.

Study design: A double blind Randomized Controlled Trial.

Methods: One hundred and eight patients scheduled for non-urgent caesarean section under spinal anaesthesia were randomized into 2 groups (control group and intervention group) using a computer generated table of numbers.

Control group; Prophylactic phenylephrine fixed dose infusion at 37.5 micrograms per minute.

Intervention group; Prophylactic phenylephrine weight adjusted dose infusion at 0.5 micrograms per kilogram per minute

Results: The two groups had similar baseline characteristics in terms of ; Age, sex, weight and height. There was 35.2% incidence of hypotension in the fixed dose group and 18.6% incidence of hypotension in the weight adjusted dose group. This difference was found to be of borderline statistical significance (p-value 0.05), and the difference in the incidence rates between the two groups was found to be statistically significant (p= 0.03). The difference in the incidence of reactive hypertension and bradycardia between the two groups was not statistically significant: p-value of 0.19 for reactive hypertension and p-value of 0.42 for the incidence of bradycardia. There was also no statistically significant difference in the use of phenylephrine boluses, use of atropine, intravenous fluid used and the number of times the infusion was stopped.

Conclusion: Among this population, the incidence of hypotension was significantly less in the weight adjusted dose group than in the fixed dose group. There was no difference in the number of physician interventions required to keep the blood pressure within 20% of baseline, and no difference in the proportion of reactive hypertension or bradycardia between the two groups. Administering prophylactic phenylephrine infusion at a weight adjusted dose of 0.5 micrograms per kilogram per minute results in a lower incidence of hypotension compared to its administration at a fixed dose of 37.5 micrograms per minute.

The study was registered under Pan African Clinical Trials Registration number PATCR 201109000311318

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