[Transcranial doppler in neurosurgery].

Transcranial doppler (TCD) is a noninvasive and easily repeatable method to measure the blood flow in basal cerebral arteries. Mean velocities of red blood cells in basal arteries are related to cerebral blood flow. Because of low peripheral resistance in cerebral arteries, diastolic velocity (V(d)) remains positive in cerebral circulation in physiological situations. The pulsativity index (PI; normal values for the middle cerebral artery=1.0+/-0.2) and end diastolic velocity (EDV; normal values for the middle cerebral artery=40+/-10 cm/s) give important information to evaluate the resistance status of small downstream arteries. A high PI (>1.4) with a low EDV (<20 cm/s) indicates a low blood flow with a high ischemic risk due to low cerebral perfusion pressure. TCD can also detect cerebral vasospasm after subarachnoid hemorrhage, but sensitivity and specificity for vasospasm diagnosis are low compared to angiography. However, a day-to-day increase in arterial blood cell velocities can help determine the vasospasm risk and/or indicate that angiography should be done.