Brain Death

Brain death is a clinical diagnosis made when there is no evidence of brainstem function on successive neurological exams. Protocols for declaring brain death vary among institutions and according to the age of the patient. The EEG is one of several tests that can help confirm the diagnosis. Complete absence of brain-derived rhythms, ECI (Fig. 8), can help confirm the clinical diagnosis of brain death. Electrocardiogram and respirator derived artifacts are often all that

Brain Dead Diagnosis
Fig. 6. Burst suppression. This 49-yr-old woman was recorded while undergoing induction with general anesthesia for vascular surgery. Bursts of bilaterally synchronous, higher amplitude mixed frequencies occur lasting 1 to 2 s, punctuated by periods of relative attenuation lasting 3 to 4 s.
Alpha Coma Eeg

Fig. 7. Alpha coma. This recording is of a 59-yr-old man on a respirator in the medical intensive care unit, partly sedated, in coma. He was unreactive to noxious stimulation. Note the diffuse and fairly continuous 9- to 9.5-Hz activities, with reversal of the usual anterior-posterior voltage gradient. This activity failed to vary with attempts to arouse the patient.

Fig. 7. Alpha coma. This recording is of a 59-yr-old man on a respirator in the medical intensive care unit, partly sedated, in coma. He was unreactive to noxious stimulation. Note the diffuse and fairly continuous 9- to 9.5-Hz activities, with reversal of the usual anterior-posterior voltage gradient. This activity failed to vary with attempts to arouse the patient.

Electrocerebral Inactivity

Fig. 8. Electrocerebral inactivity. This record is from a 66-yr-old man after a cardiopulmonary arrest. Note that the sensitivity is at 2 |V/mm and "double distance" electrode comparisons are in use. The record is dominated by amplified ECG-derived artifact. No convincing brain-derived rhythms are seen.

Fig. 8. Electrocerebral inactivity. This record is from a 66-yr-old man after a cardiopulmonary arrest. Note that the sensitivity is at 2 |V/mm and "double distance" electrode comparisons are in use. The record is dominated by amplified ECG-derived artifact. No convincing brain-derived rhythms are seen.

Table 1

EEG Criteria for Electrocerebral Inactivity

1. A minimum of eight scalp electrodes should be used

2. Interelectrode impedances should be less than 10,000 Q but more than 100 Q

3. The integrity of the entire recording system must be verified

4. Interelectrode distances should be at least 10 cm

5. The sensitivity should be at least 2 |jV/mm for at least 30 min of recording

6. Appropriate filter settings should be used

7. Additional monitoring techniques should be used when necessary

8. There should be no EEG reactivity to afferent stimulation

9. The recording should be made by a qualified technician

10. A repeat EEG should be performed if there is doubt regarding the presence of electrocerebral inactivity are observed in ECI. Several technical requirements must be met to ensure the validity of the finding. The American Electroencephalograph^ Society has published technical criteria that must be met before an EEG can be considered to fulfill ECI (Table 1).

One technicality deserving special mention is the diagnosis of brain death in infants and children. Persistence of the EEG ECI pattern must be documented in these age groups. For infants younger than 2 mo of age, two EEGs showing ECI must be obtained, separated by 48 h. For infants between 2 and 12 mo of age, the two EEGs showing ECI must be separated by 24 h. Of course, administration of sedative-hypnotic medications, for instance, barbiturates and benzodiazepines, negates the ability of the EEG to speak to brain death because the observed findings could be attributed to reversible, medication-induced effects. Variable requirements exist for the duration of time necessary since the last administration of sedative medication before the EEG can support the diagnosis of brain death. Other potential confounders of ECI must be excluded, such as hypothermia, hypotension, and severe electrolyte and glucose abnormalities, among others.

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