Aim: To compare incidences of abnormal heart rate (HR) between the phenylephrine/ephedrine protocol (P/E protocol) against the ephedrine-only (C) protocol, conventionally used for treating predelivery hypotension following spinal anesthesia for cesarean section.

Methods: Two hundred and sixty-eight parturients with pre-delivery hypotension after spinal anesthesia were equally randomized to (1) Group P/E (n = 134), phenylephrine 100 mcg in 10 mL intravenously if HR ≥ 60 beats/min (bpm), or ephedrine 6 mg intravenously if HR < 60 bpm, and 2) Group C (n = 134). The primary outcome was the incidence of the parturients with abnormal HR after vasopressor administration. The secondary outcome was the mean differences of HR and hypotensive periods during the pre-delivery period.

Results: There was no significant difference of between-group incidences of bradycardia (12.0% in Group P/E vs 6.7% in Group C, p = 0.136) and tachycardia (26.9% vs 35.8%, p = 0.114). Mean HR was 81.9 bpm (95% confidence interval [CI] 79.9, 84.3) in Group P/E, and 88.8 bpm (86.8, 90.6) in Group C (p < 0.001). The duration of hypotension in relation to the time interval from spinal anesthesia to delivery was 20.9% (95% CI 18.4-23.2) in Group P/E, and 26.5% (23.9-29.3) in Group C (p < 0.01). The calculated area under the curve (AUC) of abnormal HR in relation to time was significantly reduced only in Group P/E (p < 0.010).

Conclusions: The incidences of out-of-range HR were comparable, but the P/E protocol resulted in a lower mean HR and better control of systolic blood pressure than the ephedrine-only protocol.