The Effect of Maintaining Baseline Heart Rate and Blood Pressure on Cardiac Output Changes During Spinal Anaesthesia for Caesarean Section

摘要

Introduction Significant haemodynamic changes occur during caesarean section, which may affect uteroplacental perfusion. Anaesthetists should aim to keep blood pressure (BP) within 90% of baseline but maintenance of BP alone does not ensure cardiac output (CO) is maintained. We aimed to determine CO changes when heart rate (HR) in addition to BP is maintained at baseline. Methods CO was recorded using NICOM in 30 women undergoing elective caesarean section under spinal anaesthesia. Phenylephrine and ephedrine boluses were given to maintain BP and HR at baseline. Results CO was maintained with mean maximum increase of 0.8 L.min-1 (95% CI 0.45 to 1.19 L.min-1 , P=0.002) immediately after spinal anaesthesia. Mean maximum decrease of systolic BP was 20.4 mmHg (95% CI 8.7 to 32, P0.0001). There was no significant change in HR at any time point. CO correlated with HR (r=0.6, 95% CI 0.1 to 0.86, P=0.04) and stroke volume (r=0.7, 95% CI 0.3 to 0.9, P=0.006), while systolic BP correlated with total peripheral resistance (r=0.8, 95% CI 0.4 to 0.9, P=0.002) during the study period. Five patients required ephedrine boluses. Conclusions CO was preserved during elective caesarean section when HR was maintained at baseline. In a subset of patient’s ephedrine boluses were required in addition to phenylephrine to maintain CO. BP fell in line with total peripheral resistance despite the increase in CO.