Comparison of two different infusion rates of Phenylephrine as a Prophylaxis against Spinal Anaesthesia induced Hypotension in Elective Caesarian Sections

Abstract

Background. Spinal anaesthesia is the most commonly used technique for patients undergoing elective caesarean section. It is associated with hypotension which may lead to drop in cardiac output, decrease in placental blood flow and foetal hypoxia. Phenylephrine is commonly used to elevate arterial blood pressure by increasing systemic vascular resistance. The recommended infusion dose of phenylephrine ranges from 30 to 180µg/min. Aim: To compare the effect of two different infusion rates of phenylephrine as a prophylaxis against S/A induced hypotension and bradycardia in obstetric patients undergoing elective C- Section. Methodology: This randomized controlled was carried out in the operation theatres of KEMU affiliated Lady Aitchison Hospital Lahore , over a period of six months. After approval of institutional review board and informed consent ,220 women aged 18-40 years, planned to receive spinal anesthesia for elective caesarean section were recruited and randomly allocated into two groups. The average of the 3 readings of systolic blood pressure and heart rate was used as a baseline. Group-I received prophylactic phenylephrine infusion at 50µg/minute while Group-II received infusion at 100µg/minutes at a rate of 1ml/min immediately after spinal anaesthesia using 2ml of 0.75% Bupivacine for first 3 minutes. Infusion continued at same rate if systolic blood pressure remained between 80-100% of baseline until delivery. It was halved if systolic pressure increased > 110% of the baseline. Rescue boluses of Phenylephrine and Atropine were given if systolic pressure fell below 80% of the baseline and heart rate of < 50 beats/min respectively. Results: No significant difference was found in the frequency of hypotension in both groups ( p=0.072) whereas frequency of bradycardia was significantly lower in Group I as compared to Group II ( p=0.000) Conclusion: Prophylactic Phenylephrine infusion of 50µg/minute is better for prevention of Spinal Anaesthesia induced hypotension in patients undergoing elective caesarian section as it causes significantly less bradycardia as compared to 100ug/min infusion.