Differential change in cardiac baroreflex sensitivity estimated by sequence and spectral analysis during etomidate anesthesia

Effects of Sevoflurane Anesthesia on Carotid-Cardiac Baroreflex Responses in Humans

Sevoflurane depresses cardio-vagal baroreflex gain (ability of vagally mediated R-R interval response to arterial blood pressure change). We examined the effects of sevoflurane anesthesia on maximum buffering capacity of vagally mediated hemodynamic control (baroreflex range) by examining the entire stimulus-response baroreflex relation. Electrocardiogram and invasive arterial blood pressure were monitored in 11 healthy volunteers. Carotid-cardiac baroreflex responses were elicited by increasing neck chamber pressure (external pressure applied over the bilateral carotid sinuses) to 40 mm Hg for 5 heartbeats followed by decreasing chamber pressure by successive 15-mm Hg R-wave triggered decrements to -65 mm Hg during held expiration. R-R intervals were plotted as functions of preceding carotid distending pressure. Range, maximum gain, and operational point (relative position of the resting set point within the entire baroreflex response curve) were determined at conscious baseline, during 2% (end-tidal) sevoflurane anesthesia, without and with phenylephrine infusion to maintain conscious arterial blood pressure, and at 30, 60, 120, and 180 min after emergence from anesthesia. Sevoflurane anesthesia significantly depressed maximum gain (from 3.84 +/- 0.99 to 1.04 +/- 0.40 ms/mm Hg [mean +/- sd]; P < 0.001) and range (from 207 +/- 43 to 52 +/- 19 ms; P < 0.001) of the reflex relation, both of which recovered at 120 and 180 min after emergence. Phenylephrine infusion only partially restored these variables. The operational point was unchanged throughout the study. Our results indicate that maximum cardio-vagal compensatory response to buffer hemodynamic perturbation is depressed during sevoflurane anesthesia. Sevoflurane-induced hypotension, which produced vagal withdrawal, did not play an important role in depressing cardio-vagal reflex function.

The concentration-dependent effects of general anesthesia on spontaneous baroreflex indices and their correlations with pharmacological gains

Beat-to-beat assessment of spontaneously occurring fluctuations in heart rate and arterial blood pressure allows noninvasive determination of cardiovagal function, but little is known regarding the effects of general anesthesia on spontaneous baroreflex (SBR) indices. We examined (a) concentration-dependent effects of sevoflurane on SBR indices, heart rate variability (HRV), and blood pressure variability and (b) correlation and agreement between pharmacological baroreflex gains and SBR indices during sevoflurane anesthesia. Continuous electrocardiogram and invasive arterial blood pressure were monitored in nine healthy volunteers before, during, and for 3 h after sevoflurane anesthesia, during which end-tidal sevoflurane was maintained at 0.7%, 1.4%, and 2.0% in random sequences. We derived three SBR indices (sequence method, alpha-index, and low-frequency transfer function) and compared them with pressor and depressor test gains by the pharmacological method. HRV and blood pressure variability were analyzed at a fixed respiratory rate (12 breaths/min) in awake and anesthetized conditions. Except for low-frequency transfer function, SBR indices were depressed by sevoflurane and remained depressed for 30 min after emergence from anesthesia, compared with the conscious baseline value. Spontaneous sequence indices and high- and low-frequency powers of HRV demonstrated concentration-dependent depression. Pharmacological gains and SBR indices during anesthesia generally correlated well, but Bland-Altman analysis revealed that SBR indices had limits of agreement as large as the baroreflex gain itself. These data suggest that spontaneous indices are inadequate estimates of, and are inconsistent with, the pharmacological baroreflex gain during sevoflurane anesthesia.