Transcranial Doppler and cerebral vasospasm.

Increase in transcranial Doppler ultrasound flow velocities in the major ba sal arteries correlates with symptomatic vasospasm. Transcanial Doppler examinations are performed using a pulsed Doppler Probe via the trans temporal approach. Transcranial colour-coded real time sonog raphy can be useful and help to identify the cerebral arteries. Maximum flow velocities of >200 cm/sec are associated with cerebral ischemi a and infarction. A maximum rise in Doppler velocity of more than 50 cm/sec/24 h is correlate d 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 c onclusions about the presence or absence of vasospasm. Flow velocity is dir ectly related to cerebral blood flow. Intracranial pressure, blood pressure and volume, hematocrite and subarachnoid hemorrhage affect Doppler flow ve locities. False-negative examinations of vasospasm using TCD are associated with dist al vasospasm, severe spasm of the carotid siphon, chronic high blood pressu re and increased intracranial pressure.