Impact of Carbetocin Administration on Heart Rate When Given as an Infusion Versus as a Bolus.

The purpose of this prospective pragmatic study is to determine if an infusion of carbetocin over 10 minutes will reduce hemodynamic compromise in comparison to a rapid intravenous bolus (less than 2 seconds) during elective cesarean delivery under spinal anesthesia.

In this prospective, randomized and controlled study, each parturient will enter the operating room on the day scheduled for there surgery. All the classic monitors will be installed, along with the Edwards (Clear sight system).

Each patient will receive an antacid prophylaxis of 30 ml of sodium citrate per mouth 30 min before surgery. Baseline measures of BP (blood pressure), HR (Heart Rate), O2 Arterial Saturation will be taken before entering in the operating room, in a calm environment.

The anesthetic technique will be standardized. Spinal anesthesia will be performed in the sitting position by the anesthesiologist in charge of the patient, with the local anesthetic injected between L2 to L5 spinal level. The anesthetic solution will consist of hyperbaric bupivacaine 0.75% 10.5 mg, fentanyl 15 μg, and morphine 150 μg with a Whitacre needle 25G ou 27G. Then, the patient will be immediately placed in the supine position, with a cushion under their right hip or a left lateral tilt. Antibiotic prophylaxis will be administered to each patient before incision.

Each patient included in the study will have a phenylephrine infusion of 0.5 mcg/kg/min (lean body weight) started immediately after the injection of local anesthetic. A bolus of phenylephrine 1.5 mcg/kg (lean body weight) will be administered in case of a hypotensive episode. A hypotensive episode will be defined as 2 consecutive Systolic BP (SBP) measurements less than 20% below the baseline value. The treatment of hypotension consists of Phenylephrine 1.5 mcg/kg intravenous bolus will be administered if HR > 55 bpm or Ephedrine 5 mg intravenous bolus if HR is < 55 bpm. If only the HR is < 55 bpm, but SBP is normal, Glycopyrrolate 0.2 mg intravenous bolus will be administered and the patient will be excluded. In the case of a hypertensive episode, where systolic BP is > 120% Baseline value, treatment will consist of a decrease in the phenylephrine infusion rate by 0.2 mcg/kg/min.

In addition, each patient included in the study will receive an intravenous volume co-load of 1000 ml of Lactate Ringer administered under pressure in 5 to 10 minutes immediately after installing the intravenous catheter, and before and during the spinal anesthesia. Then, an infusion of Lactate Ringer at 300 mL/h will begin.

Surgery will begin after the confirmation of a sensory block to cold stimulus at the T4 level.

Data collection will be realized with the Edwards monitor, and HR (Heart Rate), BP (Blood Pressure), SV (Stroke Volume), SVV (Stroke Volume Variation), CO (Cardiac Output), SVR will be taken continuously every 20 seconds. HR, BP, and pulse oxymetry values will also be measured every 2.5 minutes with the applied standard monitoring, from the intrathecal injection of the local anesthetic until the neonate is born. After the injection of the study drug, those values will be measured every minute for 20 minutes (All these data are electronically recorded every 5 seconds). Hemodynamic values recorded at skin incision will be used as baseline values for comparison with hemodynamic measurements recorded over the 20 minutes following the beginning of study drug infusion.

All subjects will receive Metoclopramide 10mg intravenously at the induction of anesthesia for anti-emesis prophylaxis and Ondansetron 4 mg IV for intraoperative treatment of nausea and/or vomiting.

Prevention of post-partum hemorrhage will be with the study drug carbetocin 100 mcg given intravenously, either as a bolus or an infusion over 10 min, depending on the randomization. Two syringes per subject will be prepared by the research nurse :

1. one 3 ml syringe containing 1 ml of either carbetocin 100 mcg or normal saline same volume (according to the patient's study group);
2. one 10 ml syringe containing carbetocin 100 mcg (1 ml) diluted with 9 ml of normal saline for a total volume of 10 ml, or 10 ml of normal saline (according to the patient's study group).

The volume in the 3 ml syringe will be injected as an IV push bolus after cord clamping and the volume in the 10 ml syringe will be infused over 10 minutes at cord clamping. The study subject, the attending anesthesiologist and the anesthesiologist collecting intraoperative data will be blinded to patient group allocation. The research nurse will not be blinded to patient group allocation.

The uterine repair will be done in situ and not by exteriorization. In the eventuality that the attending obstetrician proceeded to exteriorization of the uterus for safety reasons, the patient would then be excluded from the study.

Uterine tone will be assessed by the attending obstetrician as adequate or inadequate at the end of the 10 minutes study drug infusion. If uterine tone is judged inadequate, patient care will be carried on by the attending anesthesiologist and obstetrician according to best clinical practice guidelines. These patients will be excluded from the study.

The data collection will be achieved by the ClearSight (Edwards) system. It will start before the uterine incision and will continue until 20 minutes after the beginning of the carbetocin (or normal saline) 10 minutes infusion.