[Arterial baroreflex in intravenous anesthesia and assisted spontaneous respiration]

Effects of a combined intravenous anaesthesia on the baroreceptor control of the circulation were determined in 8 healthy, unpremedicated patients, 18-50 years of age, scheduled for minor surgical procedures. The baroreflex was studied in response to brief hypotension with nitroglycerin (1-10 micrograms/kg i.v.) and quantified using the method described by Smyth, Sleight and Pickering (1969). The latter linearly correlates measurements of systolic blood pressure and the succeeding pulse interval, as obtained from recordings of the electrocardiogram. Responses in the conscious state were compared with those after administering diazepam (0.2 mg/kg i.v.), etomidate (8-20 mg i.v.) and fentanyl (0.015-0.025 mg/kg i.v.) while the patients were breathing a mixture of oxygen and nitrous oxide (1:2) during mechanically assisted ventilation. Anaesthesia led to a decrease in heart rate (17 +/- 3%) together with a slight but significant reduction in mean arterial pressure (15 +/- 4%). The mean slopes and correlation coefficients in the conscious and anaesthetized states were y = 426 + 2.33 X; r = 0.56; p less than 0.05 and y = 663 + 2.16 X; r = 0.49; p less than 0.05, respectively. Thus, no significant difference of the function of the baroreflex was observed in the conscious and anaesthetized patients. It is concluded that in contrast to inhalational anaesthesia the employed combined intravenous anaesthesia with mechanically assisted ventilation does not change this important control mechanism of the circulation in man.