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Norepinephrine to prevent hypotension after spinal anesthesia for Cesarean delivery: a dose finding study
Abstract Number: SA-09
Abstract Type: Original Research
Introduction: Norepinephrine (NE) has recently been proposed as an alternative to phenylephrine (PE) for the management of hypotension during Cesarean delivery (CD) under spinal anesthesia . A concern with PE is its propensity to reduce maternal heart rate and cardiac output, which may be detrimental in a compromised fetus [1,2]. Norepinephrine is a potent alpha agonist with some beta agonist activity, which leads to less negative chronotropic effects. The optimum bolus dose of NE required to prevent hypotension in this setting has not been established. The purpose of this study was to determine the ED90 of NE in this context.
Methods: With Institutional Ethics Committee approval and the informed consent of each participant, this study was conducted as a double-blind, sequential allocation dose-finding study, using the biased coin up-and-down design targeting ED90. Women undergoing elective CD under spinal anesthesia were recruited. Systolic blood pressure (SBP) was assessed every minute until delivery and NE was given whenever the SBP decreased to less than 100% of baseline. A dose of 3 µg was used for the first patient. The dose given to subsequent patients varied by increments or decrements of 1.0 µg (range 3-8 µg), and was determined by the primary outcome, which was the SBP maintained above 80% of baseline in the previous patient. If a patient did not respond adequately to the current dose (the SBP decreased to less than 80% of the baseline), the dose was considered to have failed and the subsequent dose for the following patient was increased to the next higher dose level. If the patient responded to the current dose, this was considered a success, and the dose for the next patient was decreased to the next lower dose with a probability of 1/9, otherwise it remained unchanged. The primary outcome was the success of the NE dose to maintain the SBP at or above 80% of baseline, from induction of spinal anesthesia to delivery of the fetus. Sample size was calculated at 45 subjects.
Results: So far we have recruited 7 patients and plan to have recruited the last patient by March 2016. Preliminary results show 86% successful maintenance of SBP at or above baseline with a range of 5-11 boluses of the study dose of NE over a 17-25 min time frame from induction to delivery. Incidences of hypotension, hypertension, bradycardia, nausea and vomiting were 14%, 14%, 0%, 29% and 0%, respectively.
Discussion: NE boluses so far appear to be effective at maintaining SBP post spinal anesthesia in elective CD, with no instances of bradycardia. The ED90 will be calculated at the end of the study. Final discussion and conclusion will be presented at the meeting.
References: 1) Anesthesiology 2015;122:736-45; 2) Anesth Analg 2010;111:1230–7