Elevated transcranial Doppler flow velocities after severe head injury: cerebral vasospasm or hyperemia?

Sixty-seven patients (45 males and 22 females) aged 2 to 70 years (mean 36 years) who had suffered closed head injury were investigated with daily transcranial Doppler (TCD) recordings. A total of 470 TCD recordings (mean 7) were made during Days 1 to 14 after admission. Blood flow velocities were determined in the middle cerebral artery (MCA) and the extracranial internal carotid artery (ICA). Twenty-seven (40%) of the 67 patients demonstrated traumatic subarachnoid hemorrhage (tSAH) on the first computerized tomography (CT) scan after the injury. Flow velocities exceeded 100 cm/second in 22 patients. Eleven (41%) of the 27 patients who showed tSAH on the first CT scan developed velocities greater than 100 cm/second, as compared to 11 (28%) of 40 patients without tSAH on CT. Two patients in whom a thick layer of tSAH was revealed on the first CT scan had MCA flow velocities exceeding 200 cm/second for several days. Measurements of cerebral blood flow (CBF) with single-photon emission CT (SPECT) were performed in six tSAH patients who showed TCD flow velocities exceeding 120 cm/second (uni- or bilaterally) to determine whether the increase in velocity reflected vasospasm or hyperemia. The SPECT studies verified ischemia in five patients but revealed general hyperemia in one. The bilateral increase in MCA flow velocities in the latter case was due to high-volume flow through the MCA secondary to elevated CBF rather than arterial narrowing. In one patient with a thick layer of subarachnoid blood on a CT scan obtained at admission, MCA flow velocities exceeded 220 cm/second bilaterally on Day 8 after the head injury. A SPECT measurement obtained on the same day reflected bilateral ischemia. In this patient flow velocities decreased, with a corresponding normalization of CBF, after 5 days of intravenous nimodipine administration. The MCA/ICA ratio correlated well with the distribution of CBF in the six patients studied using SPECT. This report suggests that vasospasm is an important secondary posttraumatic insult in patients suffering severe head injury and, in some cases, is probably treatable by administration of intravenous calcium channel blockers.