Comparison of arterial baroreflex function in humans anesthetized with enflurane or isoflurane

To compare the depressive effects of isoflurane and enflurane on the arterial baroreflex function, we examined baroreflex control of heart rate during the entire course of clinical anesthesia. Isoflurane and enflurane were found to have similar depressive effects on the baroreflex control of heart rate when used in combination with N2O and O2. Suppression in the baroreflex sensitivity, defined by the slopes of regression line (change in msec of RR interval per mm Hg increase or decrease in systolic blood pressure) was from 7.1 +/- 3.9 to 1.8 +/- 0.7 msec/mm Hg in patients given isoflurane and from 7.8 +/- 4.3 to 3.0 +/- 1.9 msec/mm Hg in those given enflurane when evaluated by a pressor test (bolus IV phenylephrine). The slope of the depressor test (bolus IV nitroglycerin) also decreased from 4.7 +/- 2.8 to 1.9 +/- 1.5 msec/mm Hg with isoflurane and from 5.6 +/- 3.2 to 2.3 +/- 1.2 msec/mm Hg with enflurane. During surgery in which anesthetic concentration invariably needed to be increased, the suppression of the baroreflex sensitivity remained unchanged in both groups of patients. During recovery, the arterial baroreflex function in patients given isoflurane recovered more rapidly than that in patients given enflurane. This difference may be related to a more minor degree of suppression of isoflurane on the autonomic nervous system compared to enflurane.