Bedside monitoring of regional cortical blood flow in comatose patients using laser Doppler flowmetry

Continuous beside monitoring of regional cerebrocortical blood flow was carried out using laser Doppler flowmetry (LDF) in four comatose patients. Newly designed thin and flexible optical probes that were easily implanted into the cortex were employed. When the patients were in a deep comatose state, the recordings revealed a conspicuous relationship to intracranial pressure. As the patients improved, the flux values gradually increased, and the recordings showed characteristic changes in the wave pattern, presumably related to the restoration of an impaired cerebral autoregulation. Changes in regional cerebrocortical blood flow were also observed during routine nursing procedures, the use of medications, and voluntary activities, as demonstrated by one patient after a complete recovery. Although the volume of tissue scanned with LDF was limited, and the flux values did not directly express regional cerebrocortical blood flow in terms of milliliters per unit volume, changes in cerebral circulation were portrayed clearly in the flow recordings. Thus, LDF, which is simple to use, permits continuous bedside monitoring of the cerebral microcirculation. Its use should improve the management of comatose patients and also open avenues for a better understanding of the cerebral circulation in pathological states.