Description

It's a randomized, double-blind, two-arm, parallel, non-inferiority, controlled trial that will be conducted in Hassan II University Hospital, Fes, Morocco. The aim of this study is to test the hypothesis that neonatal outcome, as assessed by potential of hydrogen (pH) of umbilical artery, is at least as good (non-inferior) when prophylactic continuous manually controlled infusion of norepinephrine (NE) is used to maintain blood pressure during spinal anaesthesia for elective cesarean delivery compared with the same infusion modalities of phenylephrine (PHE) with more stable blood pressure and less bradycardia.

Before starting the study, a simple randomization sequence will generate codes for two equal-sized groups. One code for each patient will be placed into a sealed, opaque, sequentially numbered envelope by a research assistant, who is not involved in patient management or data collection.

Another person not involved in subsequent patient care or assessement either, will open the envelope for each patient shortly before commencement of the study and prepared two identical 50-mL syringes according to the code contained in the envelops, patients will be randomly allocated to receive PHE or NE infusion. All the syringes were labelled as "study drug", To standardize and study the effects without affecting the potency of the drugs, vasopressor doses were taken in an equipotent ratio (12.5:1) for PHE:NE based on previous studies.

The medication used in this study are :

• NE : 4 ml vial of norepinephrine bitartrate injection, 2 mg/ml.
• PHE : 10 ml Phenylephrine hydrochloride pre-filled syringe 50 μg/ml. In group PHE, The infusion is prepared by taking 1 mg of phenylephrine (2 prefilled syringe equals to 20 ml) and diluting it with 0.9% normal saline (NS) to attain a total volume of 40 mL and a concentration of 25 μg/mL.

In group NE, Norepinephrine infusion will be prepared by taking one vial (8 mg) of norepinephrine, and diluting it with 496 ml of 0.9% normal saline (NS) to attain a concentration of NE of 16 µg/ml. 10 ml of this solution Will be diluted in 0.9% NS to reach a total volume of 40 mL and a concentration of 4 μg/mL of NE which correspond to 2 µg/ml of norepinephrine base.

Eleven milligrams of hyperbaric bupivacaine in addition to 20 μg fentanyl will be injected in the L2-L3, L3-L4 or L4-L5 intervertebral space using a 25-gauge pencil-point spinal needle in the sitting position. Block success will be assessed by sensory blockade level using pinprick test and surgery would not begin unless the sensory block reached T6 level. Patients with inadequate sensory blockade would receive general anesthesia for cesarean delivery, and will be excluded from the study.

Simultaneously with the intrathecal injection, rapid intravenous vascular volume expansion by 1000ml NS solution will be started, with a pressure infuser bag inflated.

The infusion will be initiated at a rate of 96 mL/hour (1.6 mL/minute), that correspond to a phenylephrine rate infusion of 40 μg/minute or norepinephrine rate infusion of 6.4 μg/minute. Both vasopressor infusions will be started at the same time that cerebrospinal fluid is obtained before the injection of the local anesthetic into the cerebrospinal fluid. and then manually adjusted within the range 0-144 mL/h : PHE (0-60 μg/min), NE (0-9.6 µg/min), according to values of systolic blood pressure (SBP) measured noninvasively and recorded at 1-minute intervals along the intraoperative period, with the objective of maintaining values near baseline, according to this modalities (table 1). Heart rate (HR) will be monitored continuously and recorded at 1-min interval.

SBP (% of baseline) Infusion rate (ml/min)) NE delivery rate (µg/min) PHE delivery rate (µg/min) >120% or >140 mmhg 0 0 0 100-120% 48 3.2 20 90-100% 96 6.4 40 80-90% 120 8 50 <80% 144 9.6 60

Table : Algorithm of manually controlled infusion rate and its corresponding amount of study drug (norepinephrine or phenylephrine depending on randomisation)

A researcher in the theater will manage the infusions and collect the data for analysis. Episodes of hypotension, hypertension, bradycardia and tachycardia will be recorded.

Intraoperative hypertension (defined as SBP greater than 120% of the baseline or > 140 mmhg) will be managed by stopping temporarily drug infusion. The infusion is resumed when blood pressure return to < 120% of the SBP baseline).

Postspinal hypotension (defined as decreased SBP less than 80% of the baseline or SBP< 90 mmhg reading during the period from intrathecal injection to delivery of the fetus) will be managed by increasing vasopressor infusion dose according to study protocol infusion above. In case of persistant postspinal hypotension despite increasing vasopressor doses, it's will be managed by 2-ml bolus of the infusion which correspond for parturients with NE infusion to 8µg and those with PHE to 50 μg. Additional vasopressor bolus will be given if SBP did not respond to the first dose within 2 min despite continuing the infusion.

In case of persistence of hypotension, A rescue bolus of at least ephedrine 6 mg is recommended, and repeated according to the severity and persistence of the hypotension.

After delivery and in the absence of hemorrhage, the vasopressor flow rate will be reduced in steps of 20 mL∙h-1, while maintaining an SBP >80% of baseline, a minimum delay of 5 minutes between 2 flow reductions is recommended to avoid secondary hypotension.

Intraoperative bradycardia (defined as heart rate less than 60 beats per minute without hypotension will be managed by stopping the vasopressor infusion.

If bradycardia is associated with hypotension, the patient will be managed by IV ephedrine 9 mg. If bradycardia persist or decrease below 50 beats/min after the previous measures, an IV atropine bolus (0.5 mg) should be given.

Umbilical arterial blood (UA) will be sampled from a double-clamped segment of umbilical cord by using arterial blood gas syringes. Within 20 min after clamping, umbilical blood gas will be analyzed with a bedside Blood gas Analyzer System.