[Transcranial Doppler and cerebral vasospasm]

Abstract

Increase in transcranial Doppler ultrasound flow velocities in the major basal arteries correlates with symptomatic vasospasm. Transcranial Doppler examinations are performed using a pulsed Doppler Probe via the trans temporal approach. Transcranial colour-coded real time sonography can be useful and help to identify the cerebral arteries. Maximum flow velocities of > 200 cm/sec are associated with cerebral ischemia and infarction. A maximum rise in Doppler velocity of more than 50 cm/sec/24 h is correlated with poor outcome. Using a diagnostic cutoff of 130 cm/sec a 87% positive predictive value can be obtained using TCD in the middle cerebral artery. Numerous factors affect Doppler flow velocities and may lead to erroneous conclusions about the presence or absence of vasospasm. Flow velocity is directly related to cerebral blood flow. Intracranial pressure, blood pressure and volume, hematocrite and subarachnoid hemorrhage affect Doppler flow velocities. False-negative examinations of vasospasm using TCD are associated with distal vasospasm, severe spasm of the carotid siphon, chronic high blood pressure and increased intracranial pressure.