What is Brain Death Assessment?
Brain Death, or Cerebral Circulatory Arrest, is the irreversible complete loss of brain function. This condition of brain damage is characterized by almost no volume blood flow to the brain and very high distal resistance to arterial flow.
How to use TCD for Brain Death
Transcranial Doppler (TCD) can help detect the different progression stages of cerebral circulatory arrest towards complete brain death. Distal resistance to flow increases sharply and TCD can serve as an ancillary modality for the detection and confirmation of brain death in addition to other modalities for brain death determination. Timely identification of brain death is particularly important in cases where an organ donation is an option.
The special guidelines for the diagnostic criteria of brain death must be followed very carefully. Insonation must be bilateral and include all possible windows that access the anterior and posterior circulations through the temporal and suboccipital windows. All cerebral vessels must be insonated and appropriately analyzed. One of the most important rules is that in order to accept the absence of a Doppler signal in any blood vessel, a prior valid measurement must be identified in the same vessel to ensure that the temporal window access is acceptable.
Using the Dolphin for Brain Death Detection
The Dolphin provides high Doppler sensitivity to ensure that the intracranial Doppler measurements do not miss cerebral flow. The phasic or power m-mode display functions help to identify the location (depth) of a possible blood flow along the ultrasound beam.
The special capabilities of the Dolphin TCD system support the post-processing review options in the time domain as well as in the depth domain. Since it is critical to ensure that no valid blood flow signal is missed, this unique Dolphin processing ability supports scrolling back to earlier sections of the measurement. The Dolphin allows changing the depth and closely reviewing the signal at all possible depths at each such time location.
The Dolphin Doppler processing allows increasing the sample volume significantly to as much as 20 mm and decreasing the filter to just 10 Hz in order to validate that no spectral signal is missed. Unlimited waveforms or signals can be captured and documented for each blood vessel for further proof of diagnosis.
A suspected cerebral circulatory arrest appears in various forms in the Doppler spectrum as the condition progresses. Measurements must be performed for both the anterior and posterior circulations. The various stages may include:
- Absence or reverse of end-diastolic flow;
- Reverberating flow which appears as positive and negative retrograde blood flow such that the mean positive flow is around zero;
- Small and short systolic spikes;
- No signal at all (only under the condition that a valid measurement was previously made at the same site).
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