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

† This study investigates the effects of propofol-induced changes in bispectral index (BIS) on cerebral microcirculation and oxygenation during craniotomies. † In 2 mm cerebral depth, an increase in propofol dosage resulted in increased oxygen saturation (srvO2 )w ithout reduction of capillary venous blood flow (rvCBF). † Difference in oxygen content (avDO2) and approximated cerebralmetabolicrateofoxygen (aCMRO2) decreased with an increase in propofol dosage in 2 mm cerebral depth. † Alterations in BIS showed no effect on rvCBF, srvO2 ,a nd haemoglobin amount (rvHb) or on avDO2 or aCMRO2 in 8 mm cerebral depth. † These findings suggest that the CBF/CMRO2 ratio is altered by propofol in a regionally specific fashion. 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 propofolinduced 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 21 h 21 and remifentanil 0.1‐0.4 m gk g 21 min 21 . 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: Mann‐Whitney test (*P,0.05).