Postpartum hemorrhage (PPH) due to uterine atony is a major cause of maternal morbidity and mortality. Uterotonic drugs are used to improve the muscle tone of the uterus after birth, and these are effective at reducing the incidence of PPH. Oxytocin is the most commonly used uterotonic drug to prevent and treat PPH. Large doses of this drug are asociated with adverse effects like low blood pressure, nausea, vomiting, abnormal heart rhythms and changes on ECG. Various international bodies recommend varying and high doses of oxytocin in elective cesarean sections. A study performed at Mount Sinai Hospital showed that a much smaller dose of oxytocin is required (ED95 being 0.35IU). However, most of the women included in this study were below a body mass index (BMI) of 40kg/m2. The investigators seek to find the best dose for patients with a BMI\>40kg/m2, as a higher dose may be needed in this population to contract the uterus adequately.
Postpartum hemorrhage (PPH) is one of the leading causes of death during childbirth and accounts for an estimated 140,000 deaths per year worldwide. The World Health Organization (WHO) recommends active management of the third stage of labor to prevent PPH, even in low risk patients. Prophylactic uterotonic drugs administered after delivery are the main element of active management of the third stage and have been demonstrated to reduce the incidence of PPH by up to 40%. Oxytocin is the most commonly used uterotonic in North America, however it has a very short duration of action and requires a continuous infusion to achieve sustained effect, with large doses associated with adverse effects like low blood pressure, nausea, vomiting, abnormal heart rhythms and changes on ECG. The prevalence of obesity is increasing in young women and some studies have shown that obese women have higher rates of caesarean delivery compared to non-obese women. Other studies have demonstrated an increased risk of hemorrhage due to poor uterine tone in obese women. Laboratory studies show that BMI alone appears to contribute to blunted uterine muscle responses and therefore contraction responses to oxytocin in obese women. Previous dose finding studies have excluded those women with a BMI of ≥40kgm2. Therefore, the investigators wish to perform a double-blind dose finding study using the biased coin up-and-down sequential allocation technique to determine the ED90 of oxytocin at cesarean section in those women with a BMI\>40.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
QUADRUPLE
Enrollment
30
Oxytocin administered intravenously, over 1 minute following delivery of the fetal head
Mount Sinai Hospital
Toronto, Ontario, Canada
Uterine tone 2 minutes: questionnaire
Uterine tone, defined as satisfactory or unsatisfactory by the obstetrician at 2 minutes after completion of the oxytocin injection.
Time frame: 2 minutes
Need for uterine massage: questionnaire
The obstetricians will be asked if there was any need for uterine massage beyond the initial 3 minute evaluation period following delivery.
Time frame: 20 minute
Intraoperative requirement for additional uterotonic medication
A request made by the obstetrician performing the cesarean delivery for additional uterotonic medication, due to bleeding or poor uterine tone.
Time frame: 1 hour
Calculated estimate of blood loss
Blood loss will be calculated through the difference in hematocrit values assessed prior to and at the end of 48 hours after the cesarean delivery, according to the following formula: Calculated blood loss = EBV ((Pre-op Htc-Post-op Htc)/pre-op Htc). EBV (estimated blood volume) in ml: patient's weight in kg x 85
Time frame: 24 hours
Intravenous fluid administered during surgery
The total volume (ml) of fluid administered from entering the operating room to skin closure.
Time frame: 2 hours
Hypotension: systolic blood pressure less than 80% of baseline
Systolic blood pressure \< 80% of baseline, from drug administration until end of surgery
Time frame: 2 hours
Tachycardia: heart rate greater than 130% of baseline
Heart rate \> 130% of baseline, from drug administration until end of surgery
Time frame: 2 hours
Bradycardia: heart rate less than 70% of baseline
Heart rate \< 70% of baseline or a heart rate \< 50bpm, from drug administration until end of surgery
Time frame: 2 hours
Presence of ventricular tachycardia: ECG
Presence of ventricular tachycardia as recorded by ECG, from drug administration until end of surgery
Time frame: 2 hours
Presence of atrial fibrillation: ECG
Presence of atrial fibrillation as recorded by ECG, from drug administration until end of surgery
Time frame: 2 hours
Presence of atrial flutter: ECG
Presence of atrial flutter as recorded by ECG, from drug administration until end of surgery
Time frame: 2 hours
Presence of nausea: questionnaire
The presence of nausea and number of episodes, from drug administration until end of surgery, as reported by the patient
Time frame: 2 hours
Presence of vomiting: questionnaire
The presence of vomiting and number of episodes, from drug administration until end of surgery
Time frame: 2 hours
Presence of chest pain: questionnaire
Any presence of chest pain, from drug administration until end of surgery, as reported by the patient
Time frame: 2 hours
Presence of shortness of breath: questionnaire
Any presence of shortness of breath, from drug administration until end of surgery, as reported by the patient
Time frame: 2 hours
Presence of headache: questionnaire
Any presence of headache, from drug administration until end of surgery, as reported by the patient
Time frame: 2 hours
Presence of flushing: questionnaire
Any presence of flushing, from drug administration until end of surgery
Time frame: 2 hours
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