BAROREFLEX CONTROL OF HEART-RATE DURING HIGH THORACIC EPIDURAL-ANESTHESIA - A RANDOMIZED CLINICAL-TRIAL ON ANESTHETIZED HUMANS

Baroreflex control of heart rate after cardiac sympathectomy induced by thoracic epidural anaesthesia was evaluated in 30 patients who were randomly assigned to group I (bupivacaine 0.25%), group 2 (bupivacaine 0.5%) or group 3 (control). Plasma volume expanders were given to equalise preload conditions, as assessed using transoesophageal echocardiography. All measurements were made under general anaesthesia. Baroreflex sensitivity was determined from the heart rate response to phenylephrine and nitroglycerine. There was no difference in cardiac slowing in response to phenylephrine between the three groups. Baroreflex sensitivity, measured as cardiac acceleration in response to nitroglycerine, was significantly lower (p < 0.01) in groups 1 and 2 (1.8 and 1.5 ms.mmHg−1 respectively) compared with group 3 (3.5 ms.mmHg−1) with no differences between the two bupivacaine concentrations. The results suggest that baroreflex‐mediated response to decreases in arterial pressure is dependent on the integrity of the sympathetic nervous system. Copyright © 1992, Wiley Blackwell. All rights reserved