Effects of prophylactic bolus of norepinephrine versus phenylephrine on maternal and fetal outcome during caesarean section under subarachnoid block: A randomized study

Abstract

Background: Vasopressors are the mainstay of treatment of subarachnoid block-induced hypotension (SAIH). The literature is ambiguous regarding the choice of vasopressor, the strategy of administration, and their potency ratio for proper comparison. A prophylactic bolus dosing is the preferred mode of administration for obstetric anesthesia. Thus, we undertook a study to assess the efficacy of norepinephrine (NE) and phenylephrine (PE) in preventing SAIH and compare their effects on maternal and fetal outcomes. Materials and Methods: A randomized, double-blind clinical study was conducted on 240 parturients planned for elective cesarean section under subarachnoid block (SAB). They were allocated to receive a prophylactic bolus dose of either NE 4 μg or PE 50 μg immediately after the SAB. The incidence of maternal hypotension (primary outcome); heart rate (HR), reactive hypertension, intraoperative nausea or vomiting, neonatal APGAR score, umbilical umblical cord blood pH, and the need for active neonatal resuscitation (secondary outcomes) was compared between the groups. Results: The incidence of hypotension was comparable between the groups (P = 0.42). The mean HR was significantly higher in the NE group at 2 min (83.9 ± 9.2 vs. 80.6 ± 9.3 bpm, P = 0.005), 3 min (84.4 ± 8.8 vs. 79.3 ± 11.1 bpm, P < 0.001) and 4 min (85.0 ± 9.9 vs. 79.6 ± 12.6 bpm, P < 0.001). Rest of the maternal and fetal outcomes were similar in both the groups. Conclusion: Based on the relative potency ratio of 12.5, the effect of an intermittent prophylactic bolus dose of NE is comparable to that of PE in preventing SAIH.