Comparison Between 50 Microgram Phenylephrine Bolus and Phenylephrine Infusion in Preventing Hypotension During Spinal Anaesthesia for Cesarean Section

Background: Maternal hypotension is a common complication following spinal anaesthesia for cesarean section and may adversely affect both maternal and fetal outcomes. Phenylephrine is the vasopressor of choice for preventing and treating spinal anaesthesia-induced hypotension, but the optimal mode of administration remains uncertain. Material and Methods: This quasi-experimental study included 48 ASA II parturients with uncomplicated singleton pregnancies beyond 36 weeks of gestation undergoing elective cesarean section under spinal anaesthesia. Participants were allocated into two groups (n=24 each) using the closed envelope method. Group PB received a 50 µg intravenous phenylephrine bolus, while Group PI received phenylephrine infusion at 20 µg/min immediately after spinal anaesthesia. Maternal heart rate and blood pressure were recorded at predefined intervals until 30 minutes after delivery. Data were analysed using the Student's t-test. Results: Baseline demographic characteristics were comparable between the groups. Phenylephrine infusion maintained significantly higher systolic, diastolic, and mean arterial pressures at most observation points (P<0.05). Maternal heart rate was significantly lower in the infusion group during the first 11 minutes after spinal anaesthesia. The mean phenylephrine dose administered was 212.50 ± 146.89 µg in Group PB and 500.00 ± 0.00 µg in Group PI (P<0.001). Bradycardia requiring atropine occurred in two patients (8.3%) in the infusion group, while nausea and vomiting were comparable between the groups. Conclusion: Prophylactic phenylephrine infusion at 20 µg/min provided superior haemodynamic stability compared with intermittent 50 µg bolus administration during cesarean section under spinal anaesthesia, with acceptable maternal adverse effects.

Keywords: Cesarean section; Spinal anaesthesia; Phenylephrine; Maternal hypotension; Phenylephrine infusion; Phenylephrine bolus; Haemodynamic stability.