Maintenance Infusion of Oxytocin Following Elective Cesarean Deliveries

Maintenance Infusion of Oxytocin Following Elective Cesarean Deliveries: an Up-down Sequential Allocation Dose-response Study

This study is designed to determine the minimal effective oxytocin maintenance dose required during cesarean delivery to achieve the best effect. Oxytocin is a drug which is routinely used to help contract the uterus and keep it contracted after the delivery of the baby and placenta. The aim of oxytocin is to reduce the amount of blood that might be lost. In order to determine the minimal effective dose, the investigators will conduct a dose-finding study. The first patient will receive a set oxytocin infusion. If the uterus contracts well, this is considered satisfactory and the next patient will receive the same dose. If the uterus does not contract well, this is considered unsatisfactory and the next patient will receive a higher dose. The dose for the next patient will be determined based on the results of the uterine contraction of the previous patient.

The investigators hypothesize that the ED90 of an oxytocin infusion rate to maintain a satisfactory uterine tone during a cesarean delivery in non-laboring women, would be lower than that found in previous studies without an initial bolus (less than 16 IU/h).

This study will be conducted as a prospective, double blinded clinical trial (patient, anesthesiologist and obstetrician blinded to the oxytocin dose), in an up-down sequential allocation fashion. The objective of the study is to determine the minimum effective dose of oxytocin infusion required to produce appropriate uterine contraction during and after cesarean delivery under neuraxial anesthesia in non-laboring women. For the purpose of this study, the minimum effective dose is defined to be that at which adequate response occurs in 90% of patients, i.e. ED90.

Inclusion Criteria:

• Elective uncomplicated cesarean delivery under neuraxial anesthesia
• >18 year-old with ASA status II or III, with a singleton gestation and a gestational age between 37 to 42 weeks Informed consent to participate in this study

Exclusion Criteria:

• Refusal to give written informed consent
• Allergy or hypersensitivity to oxytocin
• Body mass index ≥ 40 kg/m2on the day of admission
• A history of hypertension and/ or severe cardiac disease(s)
• Contra-indications for neuraxial anesthesia
• Conditions that predispose to uterine atony and postpartum hemorrhage such as placenta previa, multiple gestation, preeclampsia, macrosomia (≥ 4 kg), polyhydramnios, uterine fibroids in and near operating field, previous history of uterine atony and postpartum bleeding, or bleeding diathesis.