Arterial baroreflex function in humans anaesthetized with sevoflurane

Abstract

Volatile anaesthetic agents attenuate arterial baroreflex function, while noxious stimuli may modify baroreflex-induced circulatory responses during anaesthesia. We have examined baroreflex control of heart rate during the entire course of sevoflurane anaesthesia in adult patients undergoing surgical procedures. Baroreflex sensitivity was assessed in nine healthy patients undergoing general anaesthesia with sevoflurane. After an 8-10-h fast and no premedication, measurements of R-R intervals were made at conscious baseline (awake), during 2% end-tidal sevoflurane and 67% nitrous oxide before incision (anaesthesia), during surgery at 2% end-tidal sevoflurane and 67% nitrous oxide (surgery) and 20 min after extubation (recovery). Baroreflex responses were triggered by bolus i.v. injections of phenylephrine 50-100 micrograms and nitroprusside 100-200 micrograms to increase and decrease systolic arterial pressure by 20-30 mm Hg, respectively. Baroreflex sensitivities to both pressor and depressor tests were significantly depressed during anaesthesia, surgery and the recovery periods compared with awake values. Pressor test sensitivity during recovery increased significantly from that during surgery (mean 6.16 (SD 2.95) vs 4.42 (3.19) ms mm Hg-1; P < 0.05), but was still significantly less than the awake value (22.50 (17.02) ms mm Hg-1). No improvement in the depressor test sensitivity was seen during the recovery period.