British Journal of Anaesthesia 93 (5): 710–24 (2004) doi:10.1093/bja/aeh205 Advance Access publication June 25, 2004 REVIEW ARTICLES Transcranial Doppler ultrasonography in anaesthesia and

Transcranial Doppler ultrasonography (TCD) was intro-duced in 1982 by Aaslid and colleagues5 as a non-invasive technique for monitoring blood flow velocity (FV) in the basal cerebral arteries. It is now increasingly being used in anaesthesia and intensive care for research as well as in clin-ical practice. The purpose of this review is to present: the basic concepts of TCD; the current status of the information obtained; its use of assessment of vascular reactivity; and applications in anaesthesia and intensive care. Basic concepts TCD is based on the use of a range-gated, pulsed-Doppler ultrasonic beam of 2 MHz frequency.5 The ultrasonic beam crosses the intact skull at points known as ‘windows ’ and is reflected back from the moving erythrocytes in its path. The difference between the transmitted signal and the receive