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CONFIRMATORY TESTS FOR BRAIN DEATH

Tests that confirm the loss of bioelectrical activity of the brain or the cerebral circulatory arrest are optional for adults but strongly recommended for children, especially those younger than 1 year[88] ( Table 79-3 ). In several European,[2] Central American, South American, and Asian countries, confirmatory testing is required by law.[1] In the United States, the choice of tests is left to the discretion of the physician. In all cases, confirmatory tests should be used in conjunction with appropriate clinical judgment.

Electroencephalographic Recording

The EEG is the most widely available neurophysiologic test and is used in many countries and institutions as a confirmatory test for brain death [1] [2] (see Chapter 38 ). Loss of bioelectrical brain activity as shown on the EEG (i.e., isoelectric EEG) is a reliable confirmatory test

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TABLE 79-3 -- Confirmatory testing for a determination of brain death
Cerebral Angiography
The contrast medium should be injected under high pressure in the anterior and posterior circulation.
No intracerebral filling should be detected at the level of entry of the carotid or vertebral artery to the skull.
The external carotid circulation should be patent.
The filling of the superior longitudinal sinus may be delayed.
Electroencephalography
A minimum of eight scalp electrodes should be used.
Interelectrode impedance should be between 100 and 10,000 ohms.
The integrity of the entire recording system should be tested.
The distance between electrodes should be at least 10 cm.
The sensitivity should be increased to at least 2 µV for 30 minutes with inclusion of appropriate calibrations.
The high-frequency filter setting should not be set below 30 Hz, and the low-frequency setting should not be above 1 Hz.
Electroencephalography should demonstrate a lack of reactivity to intense somatosensory or audiovisual stimuli.
Transcranial Doppler Ultrasonography
There should be bilateral insonation. The probe should be placed at the temporal bone above the zygomatic arch or the vertebrobasilar arteries through the suboccipital transcranial window.
The abnormalities should include a lack of diastolic or reverberating flow and documentation of small systolic peaks in early systole. A finding of a complete absence of flow may not be reliable because of inadequate transtemporal windows for insonation.
Cerebral Scintigraphy (technetium Tc99m hexametazime)
The isotope should be injected within 30 minutes after its reconstitution.
A static image of 500,000 counts should be obtained at several time points: immediately, between 30 and 60 minutes later, and at 2 hours.
A correct intravenous injection may be confirmed with additional images of the liver demonstrating uptake (optional).
From Wijdicks EF: The diagnosis of brain death. N Engl J Med 344:1215, 2001.

for brain death. However, several problems must be considered. An isoelectric EEG can be found after drug intoxication, such as occurs with barbiturates,[97] and residual electrical activity may persist after brainstem death or after the absence of cerebral blood flow.[21]

Electrocerebral inactivity (ECI) or electrocerebral silence (ECS) is defined as no electroencephalographic activity above 2 µV/mm when recording from scalp electrode pairs placed 10 or more cm apart and with interelectrode impedances less than 10,000 ohms but more than 100 ohms. Ten guidelines for electroencephalographic recordings [98] are recommended:

  1. A minimum of eight scalp electrodes should be used.
  2. Interelectrode impedances should be less than 10,000 ohms but more than 100 ohms.
  3. The integrity of the entire recording system should be tested.
  4. Interelectrode distances should be at least 10 cm.
  5. Sensitivity must be increased from 7 µV/mm to at least 2 µV/mm for at least 30 minutes of the recording, with inclusion of appropriate calibrations.
  6. Filter settings should be appropriate for the assessment of ECS.
  7. Additional monitoring techniques should be employed when necessary.
  8. There should be no electroencephalographic reactivity to intense somatosensory, auditory, or visual stimuli.
  9. Recordings should be made only by a qualified technologist.
  10. A repeat EEG should be performed if there is doubt about ECS.

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