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

Klein, K. U.
Fukui, K.
Schramm, P.
Stadie, A.
Fischer, G.
Werner, C.
Oertel, J.
Engelhard, K.

¹Department of Anaesthesiology and
²Department of Neurosurgery, University Medical Centre of the Johannes Gutenberg-University, Langenbeckstrasse 1, 55131 Mainz, Germany

Corresponding author. E-mail: [email protected]

† Parts of this work have been presented at the Annual Meeting of the German Society of Anesthesiologists, May 9–12, 2009, and the Annual Meeting of the American Society of Anesthesiologists, October 17–21, 2009, New Orleans, LA, USA, and the Society of Neurosurgical Anesthesia and Critical Care, October 16, 2009, New Orleans, LA, USA.

Accepted May 29, 2011

BJA: British Journal of Anaesthesia 107(5):p 735-741, November 2011. | DOI: 10.1093/bja/aer227

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: 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 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.