This study is designed to determine the minimal effective oxytocin maintenance infusion required in labouring women undergoing cesarean delivery to achieve the best effect. Oxytocin is a drug that is routinely used to help the uterus to contract and keep it contracted after delivery. Consequently, it will help to reduce blood loss after delivery. 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. The next patient's infusion dose of oxytocin, will either increase or decrease, depending on how the previous patient responds in terms of uterine tone. If the response is satisfactory with the infusion dose used, the next patient will either receive the same infusion dose or it will be decreased depending on a probability of 1:9. If the response is not satisfactory, then the infusion dose will increase for the next patient. The dose for each patient will be determined based on the results of the uterine contraction of the previous patient. The investigators hypothesize that the ED90 of the oxytocin infusion rate to maintain adequate uterine tone in labouring women with induced or augmented labour undergoing cesarean delivery, following an initial effective bolus dose, would be lower than 0.74 IU/min (44 IU/h), which was found as the ED90 in a previous study, without an initial bolus dose prior to the infusion.
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 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.
Study Type
INTERVENTIONAL
Allocation
NON_RANDOMIZED
Purpose
TREATMENT
Masking
QUADRUPLE
Enrollment
40
Oxytocin will be prepared in a 1L bag of Ringer's lactate, to be infused at a rate of 125 ml/h.
Mount Sinai Hospital
Toronto, Ontario, Canada
RECRUITINGUterine tone up to discharge from the post anesthetic care unit (PACU): questionnaire
Uterine tone will be evaluated as satisfactory or unsatisfactory by the obstetrician throughout the surgery, starting at 5 minutes after the oxytocin infusion. It will also be measured at 10 minutes following the oxytocin infusion and every 10 minutes following that for the duration of the surgery. Unsatisfactory uterine tone at any time until discharge from the PACU will be considered a failure of the maintenance infusion.
Time frame: 2 hours
Calculated blood loss
Estimated blood loss will be calculated using the difference in hematocrit values prior to surgery and 24 hours post surgery, using the following formula: Calculated blood loss (mL) = 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
Need for blood transfusion
Blood product administered.
Time frame: 24 hours
Episodes of bleeding postpartum
Number of episodes of bleeding postpartum up to 24 hours post delivery.
Time frame: 24 hours
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
Requirement for additional uterotonic medication in the PACU
Any uterotonic medication administered while the patient is in PACU
Time frame: 2 hours
Requirement for additional uterotonic medication from discharge from the PACU until 24 hours postpartum.
Any uterotonic medication administered after the patient is discharged from PACU until 24 hours postpartum.
Time frame: 24 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
Hypertension: systolic blood pressure greater than 120% of baseline
Systolic blood pressure \> 120% 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
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