Mephentermine vs. Phenylephrine for Prevention and Management of Maternal Hypotension during Caesarean Section under Spinal Anaesthesia and their Effects on Foetal Outcome- A Randomised Control Trial

Abstract

Introduction: For the best maternal and foetal outcome during caesarean section under spinal anaesthesia, maintaining Systolic Blood Pressure (SBP) at 100% of the baseline is necessary. Mephentermine and Phenylephrine are both sympathomimetic drugs used for timely correction of maternal hypotension. Aim: To compare the effect of intravenous bolus administration of mephentermine and phenylephrine for prevention and management of maternal hypotension and to evaluate the foetal outcome. Materials and Methods: In this randomised double-blinded controlled trial, a total of 150 American Society of Anaesthesiologist (ASA) II scheduled for elective Lower Segment Caeserean Section (LSCS) were randomly allocated into three groups to receive the study drugs: group A received mephentermine 6 mg in 2 mL Normal Saline (NS), group B received phenylephrine 100 mcg in 2 mL NS, and group C received 2 mL NS immediately following subarachnoid block. Whenever hypotension occurred (Systolic Blood Pressure (SBP) <90 mm Hg) rescue boluses were given. Maternal haemodynamic parameters, umbilical cord blood gases, and complications were recorded from the time of sub-arachnoid block till the end of surgery. Results: There was no significant difference in the maternal haemodynamics and neonatal outcome among the three groups. It was observed that phenylephrine had quick peak effect, higher foetal umbilical pH and better neonatal outcome though statistically insignificant. Incidence of significant bradycardia (16%) and absence of intraoperative nausea and vomiting were also reported among group B. None of the neonate had APGAR (Appearance, Pulse, Grimace, Activity, and Respiration) score <7 and the umbilical pH was comparable in all the three groups (p >0.05). The time of first rescue vasopressor and the total volume of requirement was earlier and higher in group C with the mean timing of 5.87±4.37 min and mean volume of 2.68±1.58 mL respectively. Conclusion: There is a significant improvement of arterial blood pressures and better neonatal outcome observed when phenylephrine (100 mcg) and mephentermine (6 mg) are given as a prophylactic intravenous (i.v.) bolus dose immediately after subarachnoid block; especially in the initial time period between skin incision and delivery of the baby. When given as a prophylactic i.v. bolus, it had the advantage of lesser total dose requirement of the vasopressor used and better haemodynamic maintenance till the delivery of the baby