A comparison of intermittent intravenous boluses of phenylephrine and norepinephrine to prevent spinal-induced hypotension in cesarean deliveries: a randomized controlled study
Abstract Number: SAT-06
Abstract Type: Original Research
Introduction: Hypotension is a common complication of spinal anesthesia for cesarean delivery. Currently the alpha agonist phenylephrine is the vasopressor of choice for both the prevention and treatment of spinal induced hypotension (1). However, the reflex bradycardia and associated reduction in cardiac output seen with phenylephrine is of concern to the obstetric anesthetist. Of late, norepinephrine has been postulated as a better alternative to phenylephrine given its dual alpha and beta activity. When used as an infusion it is as effective at maintaining blood pressure while providing a more stable heart rate and cardiac output when compared to phenylephrine(2). In a recent study(3) to determine the ED90 of intermittent bolus doses of norepinephrine to prevent post spinal hypotension,secondary data analysis showed a 75% relative decrease in the incidence of bradycardia as compared to a similar study with phenylephrine(2). We hypothetized that equipotent intravenous bolus doses of norepinephrine administered intermittently to prevent post spinal induced hypotension at elective cesarean delivery would result in a 70% decrease in the rate of bradycardia when compared to phenylephrine.
Method: This is an ongoing double-blind randomized controlled trial. Spinal anesthesia is induced with 1.8ml of 0.75% hyperbaric bupivacaine mixed with fentanyl 10µg and morphine 100g. Women are randomized into two treatment groups to receive either phenylephrine or norepinephrine to prevent hypotension (SBP < 80% of baseline). The doses used are 100 mcg of phenylephrine(2) or 6 mcg of norepinephrine (3). Blood pressure is assessed every minute from induction of spinal anesthesia until delivery of the fetus, and a 1 mL bolus of the vasopressor is given via the peripheral IV cannula every time the SBP is below the baseline value. Ephedrine 5-10mg is given by intravenous bolus if the SBP is below baseline and the heart rate is less than 60 bpm. A bolus of ephedrine is also given if the SBP is less than 80% of baseline for two consecutive readings regardless of heart rate. The primary outcome is bradycardia(HR <50 bpm) in the pre-delivery period.
Results: Enrollment began on January 4th 2017. A sample size of 106 will achieve 80% power to detect at least a 70% decrease in the incidence of bradycardia at the significant level of 0.05. To date 30 women have been enrolled with an average enrollment rate of 7.5 study subjects per week. Recruitment success rate has been high at 73% and we have had no violations of protocol thus far. The projected date of completion for this study is April 14th 2017 and results will be presented in full at SOAP 2017.
Conclusion: This trial will be of significant importance in elucidating the role of NE intermittent boluses to prevent spinal induced hypotension during cesarean delivery.
References: 1) Ngan Kee et al. Anesth Analg 2002 94:920-6 2) Doherty et al. Anesth Analg 2012 115:1343-1350 3) Onwochei et al. Anesth Analg 2017 in press