Extracranial Carotid and Vertebral Artery Ultrasonography: Resistive Indices for Diagnosing Cerebral Brain Death

Abstract

Introduction —Transcranial Doppler (TCD) has been used to document blood flow indicative of patients who are clinically brain dead. Limitations of TCD include signal loss in the absence of an adequate acoustic window, or extensive craniotomies that interfere with TCD insonation. Additionally, when compared with duplex ultrasonography of extracranial carotid and vertebral arteries, TCD is more technically difficult to master, with limited availability in many institutions. Objective —We sought to evaluate the use of carotid and vertebral artery ultrasound resistive indices in patients with clinically diagnosed brain death. Methods —Standard carotid and vertebral duplex ultrasound protocol was used to evaluate extracranial arteries in 2 groups: I: 8 control subjects, mean age of 49 years, without evidence of carotid or vertebral atherosclerosis, and II: 8 patients, mean age of 48 years, diagnosed with brain death confirmed by electroencephalography. All patients had insignificant (< 50% stenosis) carotid and vertebral atherosclerosis. T-test was used to compare common carotid, internal carotid (ICA), external carotid, and vertebral (VERT) artery resistive indices between Groups I and II. Results —Common carotid (0.74 ± 0.04 vs. 0.88 ± 0.08), ICA (0.60 ± 0.06 vs. 1.00 ± 0.00), and VERT (0.61 ± 0.05 vs. 1.00 ± 0.00) artery resistive indices were significantly lower in normal subjects than in brain death patients ( p < 0.05). Both ICA and VERT waveforms in brain death patients demonstrated the oscillatory, “to-and-fro,” pattern already established with TCD. Conclusion —Extracranial ICA and VERT waveforms in patients diagnosed with clinical brain death have the same resistive indices and waveform patterns that have been used to identify brain death intracranially with TCD. Because standard duplex ultrasonography is the most commonly used noninvasive modality for cerebrovascular evaluation, we believe this method may be easier to understand and more readily available for the initial diagnosis of cerebral brain death.