Transcranial Doppler ultrasonography in the determination of brain death

Transcranial Doppler (TCD) ultrasonography was used to perform multiple examinations of 24 patients who sustained cranial injuries, 23 of whom progressed to death. In the 20 of these 23 patients for whom an adequate TCD signal could be obtained, a characteristic reverberating wave form pattern was observed, with an associated net flow velocity of less than 10 cm/sec in all cases. In the last patient in our study group, a reverberating pattern was also identified, however, a net flow velocity of greater than 20 cm/sec was associated with functional recovery. Correlations of neurological function, TCD tracings, and net flow velocities permitted identification of characteristic hemodynamic changes that preceded cerebral circulatory arrest. Early changes included decreased flow velocity as well as an increase in pulse pressure. Late changes consisted of a persistent increase of pulse pressure with the appearance of retrograde flow velocities during diastole. In the end stage, complete diastolic retrograde flow velocities were found. These gave rise to the characteristic reverberating pattern mentioned earlier. Identification of flow velocity reversal alone, however, proved to be inadequate for making the diagnosis of brain death. Evaluation of net flow velocity (calculated at bedside) was found to be a more sensitive determinant of brain death and closely paralleled the patients' neurological function.