Closed-loop double-vasopressor automated system vs manual bolus vasopressor to treat hypotension during spinal anaesthesia for caesarean section: a randomised controlled trial

Hypotension necessitating vasopressor administration occurs commonly during caesarean section under spinal anaesthesia. We developed a novel vasopressor delivery system that automatically administers phenylephrine or ephedrine based on continuous non-invasive arterial pressure monitoring. A phenylephrine bolus of 50g was given at 30-s intervals when systolic blood pressure fell <90% of baseline; an ephedrine bolus of 4 mg was given instead if systolic pressure fell <90% of baseline together with a heart rate <60beats.min(-1). The control group used manual boluses of either phenylephrine 100g or ephedrine 8mg, administered at 1-min intervals based on the same thresholds for systolic pressure and heart rate. This randomised, controlled, double-blinded trial involved 213 healthy women who underwent elective caesarean delivery under spinal anaesthesia using 11mg hyperbaric bupivacaine with 15g fentanyl and 100g morphine. The automated vasopressor group had better systolic pressure control, with 37/106 (34.9%) having any beat-to-beat systolic pressure reading <80% of baseline compared with 63/107 (58.9%) in the control group (p<0.001). There was no difference in the incidence of reactive hypertension, defined as systolic pressure > 120% of baseline, with 8/106 (7.5%) in the automated vasopressor group vs 14/107 (13.1%) in the control group, or total dose of vasopressors. The automated vasopressor group had lower median absolute performance error of 8.5% vs control of 9.8% (p=0.013), and reduced incidence of nausea (1/106 (0.9%) vs 11/107 (10.3%), p=0.005). Neonatal umbilical cord pH, umbilical lactate and Apgar scores were similar. Hence, our system afforded better control of maternal blood pressure and reduced nausea with no increase in reactive hypertension when compared with manual boluses.