Effect of Two Different Doses of Intravenous Phenylephrine on the Prevention of Oxytocin Induced Hypotension in Lower Segment Caesarean Section Under Subarachnoid Block: A Randomised Controlled Study

Introduction: Postpartum haemorrhage with an atonic uterus is one of the leading causes of maternal mortality during Lower Segment Caesarean Section (LSCS) in nearly 50% of cases. Oxytocin is the most commonly administered drug for achieving post-delivery adequate uterine contractions and placenta expulsion, thereby preventing postpartum haemorrhage. Co-administration of phenylephrine during LSCS under spinal anaesthesia inhibits Oxytocin-induced hypotension. Aim: To compare the effectiveness of co-administration of two different doses of phenylephrine with oxytocin in preventing the incidence of Oxytocin-induced hypotension. Materials and Methods: A randomised, double-blinded controlled trial was in the Department of Anaesthesiology, SMS Medical College and Attached Group of Hospitals, Jaipur, Rajasthan, India from August 2021 to July 2022, involving 120 parturients with American Society of Anaesthelsiologists (ASA) grade second undergoing LSCS under subarachnoid block. They were randomised into three groups: Group A received oxytocin 3U with normal saline, Group B received Oxytocin 3U with Phenylephrine 50 mcg, and Group C received Oxytocin 3U with Phenylephrine 75 mcg administered intravenously over five minutes after the baby's extraction. The incidence of hypotension, requirement for the total rescue dose of Phenylephrine, and side effects were recorded. Statistical analysis was performed using Analysis of Variance (ANOVA) and Chi-square test. Results: Demographic parameters such as age, height, weight, gestational age, and duration of surgery were comparable in all groups. The incidence of hypotension (Group A (Control): 77.5%, Group B (PE50): 47.5%, Group C (PE75): 22.5%, p<0.001), lowest Mean Arterial Pressure (MAP) after Oxytocin infusion (Group A: 67.80 +/- 6.16 mmHg, Group B: 68.23 +/- 3.96 mmHg, Group C: 72.50 +/- 5.87 mmHg, p<0.001), dose of rescue vasopressor requirements (Group A: 75.5 +/- 56.61, Group B: 40 +/- 50.89, Group C: 17.50 +/- 34.99, p<0.001), and incidence of side effects were significantly lower in Group C compared to Group B and Group A. Conclusion: Compared to Phenylephrine 50 mcg, the co-administration of Phenylephrine 75 mcg with Oxytocin 3U reduces the incidence of Oxytocin-induced hypotension and the need for rescue vasopressors during LSCS under subarachnoid block.