Cerebral vasospasm is typically the outcome of SAH as a result of an aneurysm rupture. Early detection of vasospasm is critical since it allows timely intervention.
TCD is rather specific for this condition, and allows non-invasive, continuous bed-side monitoring.
Vasospasm is characterized by increased velocities due to arterial narrowing. Severe vasospasm is when mean velocities exceed 200 cm/sec, moderate conditions are with mean velocities between 120-200 cm/sec, and moderate vasospasm is for mean velocities near 120 cm/sec. Additionally, velocities in the middle cerebral artery can be compared to internal carotid artery velocities, and the resulting ratio (Lindergaard index) can indicate cerebral vasospasm when it is greater then 3.