Hemodynamically significant cerebral vasospasm and outcome after head injury: a prospective study. 
The authors prospectively investigated cerebral hemodynamic changes in 152 patients with head injuries to clarify the relationship between cerebral vasospasm and outcome.  They also sought to determine the most clinically meaningful criteria for diagnosing cerebral vasospasm.  Patients with varying degrees of moderate-to-severe head injury were monitored using transcranial Doppler (TCD) ultrasonography and intravenous 133Xe-cerebral blood flow (CBF) measurements.  Outcome was determined at 6 months.  Using TCD ultrasonography, mean flow velocities were determined for the middle cerebral artery (V(MCA), 149 patients) and basilar artery (V(BA), 126 patients).  Recordings of the mean extracranial internal carotid artery velocity (V(EC-ICA)) were also performed to determine the hemispheric ratio (V(MCA)/V(EC-ICA), 147 patients).  Cerebral blood flow measurements were obtained in 91 patients.  Concurrent TCD and CBF data from 85 patients were used to calculate a "spasm index" (the V(MCA) or V(BA), respectively, divided by the hemispheric or global CBF).  The authors investigated the clinical significance of elevated flow velocity, hemispheric ratio, and spasm index.  Patients diagnosed as having MCA or BA vasospasm on the basis of TCD-derived criteria alone had a significantly worse outcome than patients without vasospasm.  When CBF was considered, hemodynamically significant vasospasm, as defined by an elevated spasm index, was even more strongly associated with poor outcome.  Stepwise logistic regression analysis confirmed that hemodynamically significant vasospasm was a significant predictor of poor outcome, independent of the effects of admission Glasgow Coma Scale score and age.  On the basis of the results of this study, the authors suggest that the important factor impacting on outcome is not vasospasm per se, but hemodynamically significant vasospasm with low CBF.  These findings show that vasospasm is a pathophysiologically important posttraumatic secondary insult, which is best diagnosed by the combined use of TCD and CBF measurements.