Comparision of prophylactic infusion of Phenylephrine versus Norepinephrine for the prevention of post spinal hypotension in parturients undergoing elective caesaeran section-A double blinded, non inferiority, randomised controlled trial

Spinal anaesthesia is the technique of choice for elective caesarean delivery; however this technique results in hypotension in the vast majority of women if not actively prevented. The consequences of spinal hypotension in this setting are proportional to the severity and include nausea and vomiting, decrease in uteroplacental blood flow, fetal acidosis, and rarely, cardiovascular collapse. Without prophylactic Vasopressors, post spinal hypotension affects neatly 60% of women during caesarean delivery; thus using vasopressors have been highly recommended for routine prevention of post spinal hypotension during caesarean delivery. Phenylephrine is a potent α -adrenergic receptor agonist as emerged as the vasopressor of choice for management of post spinal hypotension. It’s use is often associated with a dose related reflexive slowing of maternal heart rate(HR) and a corresponding decrease in cardiac output(CO).Although the clinical significance of these decreases in HR and CO in healthy patients with unstressed fetuses is unknown, concern has been expressed that there may be potential for harm in the presence of a compromised fetus. Hence the use of norepinephrine which is characterized by α -adrenergic agonistic activity in addition to a weak β -adrenergic agonistic activity, is recommended as vasopressor with minimal cardiac depressant effect to prevent maternal hypotension. These pharmacologic properties would make norepinephrine an attractive alternative to phenylephrine and ephedrine in obstetric anaesthesia. We postulated that norepinephrine might therefore be an effective vasopressor for maintaining blood pressure during spinal anaesthesia with less tendency to decrease Heart rate and Cardiac output.