Effect of phenylephrine rescue injection on hypotension after spinal anaesthesia for caesarean delivery when guided by both heart rate and SBP during an early warning window

BACKGROUND Spinal anaesthesia is now the most common technique for caesarean delivery. However, because of the intermittent nature of noninvasive blood pressure (NIBP) measurements, maternal blood pressure may become hypotensive between the measurements. There is thus an inbuilt delay before the anaesthesiologist can intervene to counteract the hypotension. Based on the principle that changes in blood pressure can induce compensatory changes in the heart rate (HR), combining the NIBP with real-time HR, we designed two warning windows to predict hypotension and hypertension. OBJECTIVE To evaluate whether phenylephrine administration guided by these warning windows would help maintain haemodynamic stability. SETTING A teaching hospital. DESIGN A randomised controlled trial. PATIENTS One hundred and ten pregnant women scheduled for elective caesarean delivery were enrolled, from which, after exclusions, 86 were eligible for the study. INTERVENTIONS All eligible patients received a continuous intravenous infusion of phenylephrine as soon as spinal anaesthesia was initiated. Thereafter, patients were randomly assigned to two groups. In the test group (Win-Group): rescue phenylephrine administration was triggered by an early warning window of HR above 100 beats per minute (bpm) and SBP 90 to 110 mmHg; pausing the infusion phenylephrine was triggered by a HR lower than 60 bpm and SBP greater than 90 mmHg. In the control group, phenylephrine was guided by BP only when it appeared on the monitor: SBP less than 90 mmHg was the trigger for administering rescue phenylephrine; SBP greater than 110 mmHg was the trigger for pausing the phenylephrine infusion. MAIN OUTCOME MEASURES The primary outcome was incidence of hypotension. Secondary outcomes were the incidence of hypertension and other adverse haemodynamic events. RESULTS The incidence of hypotension was significantly lower in the Win-Group than in the BP-Group (27.8 vs. 66.7%, P = 0.001). The minimum SBP was significantly higher in Win-Group than in BP-Group (93.9 ± 9.49 vs. 86.7 ± 11.16 mmHg, P = 0.004). There was no significant difference in the incidence of hypertension between groups. CONCLUSION After spinal anaesthesia for caesarean delivery, when phenylephrine infusion is guided by HR along with BP from a warning window it effectively reduces the incidence of hypotension without any significant effect on incidence of hypertension. TRIAL REGISTRATION Chictr.org.cn; Identifier: ChiCTR 2100041812.