Norepinephrine versus phenylephrine infusion for prevention of hypotension after spinal anaesthesia in elective cesarean section-A randomised double blinded study.

Following approval from the Institutional Ethical Committee, informed and written consent will be taken from 60 parturients of American Society of Anaesthesiologists Physical status (ASA) class II undergoing  elective lower segment cesarean section  under spinal anaesthesia.Randomization of parturients will be done by shuffled sealed opaque envelope technique.

A thorough pre-anesthetic evaluation (PAE) will be  done 24 hours prior to the elective cesarean section. Standard monitoring with electrocardiography (ECG), automated NIBP (noninvasive blood pressure), heart rate (HR) and pulse oximetry (SpO2) will be done and baseline values of SBP (systolic blood pressure), DBP (diastolic blood pressure), MAP (mean arterial pressure), HR, ECG and saturation will  be recorded and monitored intra-operatively by GE B125M monitor.

   Group NE- 30 parturients will receive3.2 mcg/min of norepinephrine as iv infusion

Group PE - 30   parturients will receive 40mcg/min of phenylephrine as IV  infusion

Under  asepsis, a subarachnoid block will be performed in a sitting position using 25G Quincke spinal needle and injection bupivacaine 0.5%(Heavy) 2ml will be given intrathecally. Infusion of the study solution will be started as soon as subarachnoid block is given. A solution of either phenylephrine 100mcg/ml (group PE) or norepinephrine 8 mcg/ml (group NE)  at a rate of 24ml/hr which has been prepared in 50ml syringes  will be administered through a seperate  intravenous line. The automated NIBP cycling time will be kept at 1 min interval after intrathecal injection until delivery of fetus.Any incidence of SBP less than or equal to 80% of baseline or an absolute value less than 100 mm hg will be treated with bolus of 1/2ml study drug in increments till the BP is normalized and the number of episodes will be noted and total number of increments will be noted .If there is any episode of hypertension defined as SBP greater than or equal to 120% then the study drug infusion will be stopped till the BP is < 120% and infusion is restarted and number of episodes of hypertension will be noted.If there is bradycardia which is defined as heart rate <60beats/min will be treated by giving intravenous injection atropine0.6mg.

The study will be terminated on delivery of the baby and the study solution will be continued at the discretion of the attending anaesthesiologist till the end of surgery . Episodes of intraoperative nausea and vomiting will be recorded using the nausea vomiting score: 0: None;1:Reported nausea without vomiting;2:observed vomiting8 . Intra operative nausea and vomiting will be treated with injection of ondansetron 4mg I/v at a score greater than or equal to 1. Immediately after delivery,APGAR scores will be assessed and recorded at 1 min and 5 min .