Evaluation of the uterotonic effect of Carbetocin vs Oxytocin in elective caesarean sections

Post-partum haemorrhage (PPH) is the most important cause of maternal morbidity and mortality. Main cause of PPH is uterine atony. Uterotonic agents and step-wise surgical measures are used for its management. PPH can result in severe anaemia, need for blood transfusion, coagulopathy and end organ damage

Oxytocin and carbetocin are commonly used uterotonic agents. Both the drugs are being used in our institution as part of standard of care during cesarean section.

Oxytocin is the most widely used and available first line uterotonic agent. It brings about its action by binding to the G protein receptors present in the myometrium which will trigger the release of calcium from the sarcoplasmic reticulum. This will further enhance the uterine contractions, which is important in maintaining post- partum haemostasis. Oxytocin is given to the mother as an intravenous (iv) infusion after the delivery of the baby. It is a relatively safe drug with and adverse effect profile consisting of reflex tachycardia, transient decrease in systemic blood pressure, nausea and vomiting. The effect of oxytocin can be limited by its heat susceptible nature and need for cold chain storage.

Carbetocin is an oxytocic analogue with a similar mechanism of action. It acts at the same receptors as that of oxytocin on the myometrium, triggering the release of calcium and further enhancing the uterine contractions. A single dose of this drug is said to be as effective as a continuous infusion of oxytocin and thus it saves the need of an additional iv cannula and the discomfort to the mother in this critical period. The major advantage over the traditionally used oxytocin is a longer duration of action and a heat stable nature which reduces its need for cold chain storage. It has side effects similar to oxytocin - it causes nausea and vomiting, abdominal pain, hyperthermia, tachycardia, hypotension, headache.

Through this study we aim to assess the effect of both these drugs on uterine tone and try and understand if Carbetocin can be a better substitute to oxytocin in our theatres, despite its high cost.

After institutional ethical committee clearance, written informed patient consent and CTRI clearance, parturients undergoing caesarean section under spinal anaesthesia will be randomized to two groups (group O and group C) using computer generated random sequence of numbers. Concealment will be achieved by closed envelope technique.

After delivery of baby, Group O patients will receive oxytocin 3 units IV bolus over 20 seconds and followed by infusion of 3 units per hour for 4 hours. Group C will receive carbetocin 100 mcg IV over 1 minute followed by saline infusion 3 ml per hour for 4 hrs.

Uterine tone will be assessed by operating surgeon at 3, 6, 9 and 15 minutes after giving study drugs with a 11-point numerical rating scale from 0 to 10, with 0 being no tone and 10 being excellent tone. Further uterotonic agents (oxytocin/methylergometrine/prostaglandin F2α) will be given on demand from the operating surgeon and it will be noted.

Haemodynamic effects including heart rate, systolic blood pressure, mean arterial pressure will be noted during the same time points. Blood loss will be assessed and if it exceeds 1000 ml, PRBC will be transfused.

Any adverse effects associated with the use of study drugs including nausea and vomiting, abdominal pain, hyperthermia and headache will be noted.