Closed-Loop Feedback Computer-Controlled Phenylephrine for Maintenance of Blood Pressure During Spinal Anesthesia for Cesarean Delivery: A Randomized Trial Comparing Automated Boluses Versus Infusion.

BACKGROUND: We previously described the use of closed-loop feedback computer-controlled infusion of phenylephrine for maintaining blood pressure (BP) during spinal anesthesia for cesarean delivery. In this study, we report a modified system in which phenylephrine is delivered by intermittent boluses rather than infusion. We hypothesized that the use of computer-controlled boluses would result in more precise control of BP compared with infusions. METHODS: Two hundred fourteen healthy patients having spinal anesthesia for elective cesarean delivery were randomized to have their systolic BP maintained by phenylephrine administered by computer-controlled continuous infusion or computer-controlled intermittent boluses. From induction of anesthesia until the time of uterine incision, a noninvasive BP monitor was set to cycle at 1-minute intervals. In the infusion group, the infusion rate was automatically adjusted after each BP measurement using a previously described algorithm. In the bolus group, the algorithm was modified so that the mass of drug that would have been delivered over 1 minute was instead injected as a rapid intravenous bolus after each BP measurement. The precision of BP control was assessed using performance error calculations and compared between groups, with the primary outcome defined as median absolute performance error, and the latter being a measure of inaccuracy showing an average of the magnitudes of the differences of measured BP values above or below the target values. RESULTS: The precision of BP control was greater, as shown by smaller values for median absolute performance error, in the bolus group (median 4.38 [quartiles 3.22, 6.25] %) versus the infusion group (5.39 [4.12, 7.04] %, P = .008). In the bolus group, phenylephrine consumption was smaller; this was associated with smaller values for median performance error compared with the continuous infusion group (P

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