ARTERIAL BAROREFLEX ATTENUATION DURING AND AFTER CONTINUOUS PROPOFOL INFUSION

The reduction of arterial blood pressure produced by propofol may be, in part, attributable to impaired baroreflex integrity. The purpose of this study was to investigate arterial baroreflex sensitivity during and after continuous propofol infusion. In urethane anaesthetized rabbits, left renal sympathetic nerves were exposed and placed on a bipolar silver electrode to record renal sympathetic nerve activity (RSNA). Mean arterial pressure (MAP) via a femoral artery and heart rate (HR) by electrocardiogram were continuously recorded. The rabbits were divided into two groups of eight each: Group 1, propofol 5 mg . kg-1 bolus followed by infusion 0.5 mg . kg-1 . min-1; Group 2, propofol 2 mg . kg-1 bolus followed by 0.2 mg . kg-1 . min-1. Phenylephrine pressor and sodium nitroprusside (SNP) depressor tests were carried out before propofol was started (control), at 15 and 30 min during 30 min infusion, and at 15, 30 and 60 min after its discontinuation. The change of RSNA was plotted with respect to every 5 mmHg increment and decrement of MAP to construct sympathetic baroreflex sigmoid curves, and to evaluate baroreflex sensitivity. The baroreflex sensitivity was also evaluated by calculating the ratio of maximum increase of RSNA or HR to SNP-induced maximum decrease of MAP (DELTARSNA/DELTAMAP, DELTAHR/DELTAMAP). Despite the same decreases or increases in MAP, RSNA was attenuated after 15 and 30 min of propofol infusion in both groups compared with control (P < 0.05). Decreased DELTARSNA/DELTAMAP gradually returned to the control level 60 min after discontinuation of propofol in Group 1. The baroreflex sensitivity for control of HR was attenuated only at 30 min in the higher propofol infusion group (P < 0.05). It is concluded that propofol attenuates baroreflex sensitivity for control of RSNA in a dose-dependent manner during infusion. Although recovery from anaesthesia is rapid, our data indicate that the attenuated arterial baroreflex may persist after discontinuing propofol infusion.