Human cerebral microcirculation and oxygen saturation during propofol-induced reduction of bispectral index

Abstract

Background. Propofol reduces cerebral blood flow (CBF) secondary to cerebral metabolic depression. However, in vitro and in vivo studies demonstrate that propofol directly dilates the vascular smooth muscle. This study investigates the effects of propofol-induced changes in bispectral index (BIS) on cerebral microcirculation and oxygenation during craniotomies. Methods. In 21 craniotomy patients undergoing routine craniotomy, anaesthesia was maintained with propofol 4-10 mg kg-1 h-1 and remifentanil 0.1-0.4 μg kg-1 min-1. Propofol concentration was adjusted to achieve higher BIS (target 40) or lower BIS (target 20). Regional measurements of capillary venous blood flow (rvCBF), oxygen saturation (srvO2), and haemoglobin amount (rvHb) at 2 mm (grey matter) and 8 mm (white matter) cerebral depth were randomly performed at higher and lower BIS by combined laser-Doppler flowmetry and spectroscopy. Calculations: approximated arteriovenous difference in oxygen content (avDO2) and cerebral metabolic rate of oxygen (aCMRO2). Results. mean values (SD). Statistics: MannWhitney test (*P<0.05). Results. Human cerebral microcirculation and oxygen saturation were assessed at propofol dosages 5.1 (2.3) mg kg-1 h-1 [BIS 40 (9)] and 7.8 (2.1) mg kg -1 h-1 [BIS 21 (7)]. Propofol-induced reduction in BIS resulted in increased srvO2 (P=0.018), and decreased avDO2 (P=0.025) and aCMRO2 (P=0.022), in 2 mm cerebral depth, while rvCBF and rvHb remained unchanged. In 8 mm cerebral depth, srvO2, rvCBF, rvHb, and also calculated parameters avDO2 and aCMRO2 remained unaltered. Conclusions. Findings suggest alteration of the CBF/CMRO2 ratio by propofol in cortical brain regions; therefore, it might be possible that propofol affects coupling of flow and metabolism in the cerebral microcirculation. © The Author [2011]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.