title: 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).
  
  
  METHODS
  Mann-Whitney 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 aCMRO(2) (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.
authors.affiliation: Department of Anaesthesiology, University Medical Centre of the Johannes Gutenberg-University, Germany. kuklein@uni-mainz.de
authors.forename: K U
authors.initials: KU
authors.lastname: Klein
authors.forename: K
authors.initials: K
authors.lastname: Fukui
authors.forename: P
authors.initials: P
authors.lastname: Schramm
authors.forename: A
authors.initials: A
authors.lastname: Stadie
authors.forename: G
authors.initials: G
authors.lastname: Fischer
authors.forename: C
authors.initials: C
authors.lastname: Werner
authors.forename: J
authors.initials: J
authors.lastname: Oertel
authors.forename: K
authors.initials: K
authors.lastname: Engelhard
mesh_terms: D000328:Adult; D018686:Anesthetics, Intravenous / Q000378:metabolism / Q000494:pharmacology*; D001921:Brain / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D056805:Consciousness Monitors; D003399:Craniotomy; D004305:Dose-Response Relationship, Drug; D005260:Female; D006454:Hemoglobins / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008297:Male; D008833:Microcirculation / Q000187:drug effects*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000378:metabolism*; D010880:Piperidines; D015742:Propofol / Q000378:metabolism / Q000494:pharmacology*; D000077208:Remifentanil; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D018686:Anesthetics, Intravenous; D006454:Hemoglobins; D010880:Piperidines; D000077208:Remifentanil; D010100:Oxygen; D015742:Propofol