Comparison of prophylactic infusion of phenylephrine and norepinephrine for prevention of hypotension in elective caesarean section under spinal anaesthesia- A randomized controlled study

Background:Post spinal hypotension can have deleterious effects on parturient and foetus in caesarean section if not prevented. Norepinephrine has alpha agonistic activity with weak beta agonistic activity, so may be more effective in maintaining cardiac output of parturient. Aims:To compare the effects of prophylactic infusion of phenylephrine and norepinephrine on cardiac output as a primary outcomeand heart rate, mean arterial pressure, stroke volume, and systemic vascular resistance of parturient, neonatal Apgarscore and umbilical blood gas analysis as secondary outcomes.Method:Eighty six healthy patients undergoing elective caesarean section under spinal anaesthesia were randomized into two groups. Group P received infusion of phenylephrine (100 µg/ml)intravenous (iv) and Group N received infusion of norepinephrine (5µg /ml) iv just after intrathecal drug administration.The pre-defined algorithm was used to adjust the infusion rate according to mean arterial pressure. All haemodynamic parameters and total volumes of vasopressor upto the time of uterine incision and upto 30 min after starting drug infusion were recorded. Data were compared using unpaired Student t-test and Chi square test. P value less than 0.05 was considered significant. Results: Group N had higher cardiac output at 1 min (p=0.01),3 min(p=0.0001),6 min(p=0.006), 9 min(p=0.001) in comparison to group P. Group P had lower heart rate at 1 min (p=0.0003),3 min(p=0.0001),6 min(p=0.0001), 9 min(p=0.0001) and 12 min(p=0.0078) in comparison to group N. Systemic vascular resistance was higher in group P at 6 min(p=0.004),9 min(p=0.001) and 12 min (p=0.04). Total volume of vasopressor required to maintain mean arterial pressure was higher in group N(p<0.0001). Conclusion: Norepinephrine has greater efficacy to maintain cardiac output, with greater heart rate in comparison to phenylephrineduring spinal anaesthesia for caesarean section