Clinical Applications
Traumatic brain injury (TBI) is one of the leading causes of disability and death. Cerebral vascular injury and hemodynamic compromise is a significant contributor to poor outcome in patients with TBI.
Our current understanding of the mechanisms underlying cerebrovascular damage in TBI is limited. Disturbances in cerebral hemodynamics with an early phase of cerebral hypoperfusion followed by hyperemia and secondary elevations in ICP may be one possible mechanism. Chan, et al, used TCD to detect hypoperfusion in TBI patients and showed that an initial Vmean of < 28 cm/s N

was associated with 80% likelihood of early death.78 In a prospective study of 36 children with moderate to severe TBI, diastolic flow velocity 1.31 (indicative of high cerebrovascular resistance) at the time of admission was also associated with poor prognosis.

The usefulness of early Transcranial Doppler (TCD)-directed therapy was examined in a study of adults with severe TBI. TCD measurements were available within 18 ± 11 minutes after admission and were considered abnormal when two out of three measures were outside the following range: Vmean < 30 cm/s, Vd 1.4. Patients with abnormal TCD received treatment to increase cerebral perfusion pressure and/or decrease cerebral edema. Cerebral invasive monitoring was available at ~4 hours after admission and showed similar cerebral perfusion pressure and jugular venous oxygen saturation between the two groups despite increased intracranial pressure in patients with abnormal TCD.

These findings show that early TCD monitoring can help prevent cerebral hypoperfusion, which may help reduce the extent of secondary ischemic injuries in TBI patients with elevated ICP. TCD measures predictive of clinical outcome that can be used as therapeutic targets in clinical trials of TBI will have a significant impact on how we manage TBI in the future.

Resources

Purkayastha S, Sorond F. Transcranial Doppler ultrasound: technique and application. Semin Neurol. 2012;32(4):411–420. doi:10.1055/s-0032-1331812