USE OF NEAR-INFRARED SPECTROSCOPY TO ESTIMATE CEREBRAL BLOOD-FLOW IN CONSCIOUS AND ANESTHETIZED ADULT SUBJECTS

Near infrared spectroscopy (NIRS) can be used to quantify cerebral hae modynamic states noninvasively and to estimate cerebral blood flow (CB F). In the first part of this study we, have compared CBF measurements in conscious and anaesthetized subjects. in the second part we have c ompared paired measurements made during anaesthesia, first on the scal p and then the dura after craniotomy. Mean CBF was 17 (SD 7) ml 100 g( -1) min(-1) in the conscious subjects compared with 21 (8) ml 100 g(-1 ) min(-1) on the scalp during anaesthesia (P > 0.1). Mean CBF on the d ura was 68 (21) ml 100 g(-1) min(-1) (P < 0.0001). Computer modelling suggests that the difference in magnitude between scalp and dura measu rements of CBF is likely to be caused by the optical effect of extrace rebral tissue which powerfully scatters light passing through it but d oes not contribute significantly to the measured CBF because it has on ly a small blood content itself. The results lend support to this meth od of estimating CBF although formal validation by comparison with an established technique is needed.