Measures of brain Electrical Activity
Measures of brain Electrical Activity
EEG
- Most popular and validated test worldwide, though there has been a recent move away
- Isoelectric EEG may be mimicked by conditions such as hypothermia, barbiturates, or other central nervous system (CNS) depressants - hence it is of little value when these are suspected
Somatosensory or Auditory Evoked Potential (SSEP)
- A peripheral stimulus given (i.e. median nerve} and a response is measured at the contralateral primary sensory cortex
- Absence of transmission measured 20 ms (N20 response) after stimulation suggests brainstem dysfunction
- May be useful where coma of toxic aetiology is suspected - short-latency responses that are absent in brain death but preserved in toxic and metabolic disorders
Measures of Blood Flow
Measures of Blood Flow
Cerebral Angiography
(4 vessel)
(4 vessel)
- Contrast medium is injected in the aortic arch under high pressure to reach both anterior and posterior circulations
- Confirmatory testing demonstrates absence of intracerebral filling beyond the carotid or vertebral arteries' entry to the skull
Transcranial Doppler
- Useful only if a reliable waveform is found
- Complete absence of flow may not be reliable if inadequate windows exist
- Confirmatory testing should demonstrate either reverberating flow or small systolic peaks in early systole
Cerebral Scintigraphy
- Non-invasive and safe measure of cerebral blood flow
- No patient transport required if a portable gamma camera is available
- Technetium 99 m is given by intravenous bolus with images obtained by a gamma camera every 3 seconds for a total of 60 seconds
- External carotid flow is either digitally subtracted or excluded by forehead tourniquet
- Confirmatory testing demonstrates no radionuclide localization in the middle cerebral artery, anterior cerebral artery, or basilar artery territories of the cerebral hemispheres
Spiral CT or MRI angiography
- Increasingly available and investigated as ancillary tests
- Confirmatory testing demonstrates absence of intracerebral filling beyond the carotid or vertebral arteries' entry to the skull