What TCD finding is consistent with vasospasm following subarachnoid hemorrhage?

The finding that indicates vasospasm following subarachnoid hemorrhage is greatly increased mean velocities in the middle cerebral artery. This increased velocity is a direct physiological response to the narrowing of the artery caused by vasospasm. When the arteries narrow, the same volume of blood is forced through a smaller diameter, resulting in higher velocities to maintain adequate blood flow.

In the context of TCD (transcranial Doppler) ultrasound, these increased mean velocities are often used to assess the degree of vasospasm. Clinicians monitor these velocities because they can indicate the severity of the condition and guide treatment decisions. Thus, recognizing this pattern of increased velocities is crucial in managing patients who have experienced a subarachnoid hemorrhage, as timely interventions can prevent further complications.

Other findings, such as absence or greatly diminished diastolic flow, may reflect severe ischemia or disturbed flow dynamics but do not specifically indicate active vasospasm, which is characterized by the marked increase in blood flow velocities. Retrograde flow would also indicate a significant pathological process but differs from the classical presentation of vasospasm.