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BRAIN DEATH CRITERIA1*

 

Brain Death2* is a clinical diagnosis which can be made when there is complete and irreversible cessation of all brain function. Since it is now technically possible to sustain cardiac, circulatory respiratory and other organ function after the brain has ceased to be alive, a diagnosis of brain death can be made before the heart beat stops.

The diagnosis of brain death is based primarily on clinical criteria. A confirmatory laboratory test may be done to supplement the clinical diagnosis.

An individual with irreversible cessation of all brain function, including the brain stem, is dead.

 

Historical Aspects

In 1564, Versalius a famous anatomist is said to have conducted an autopsy in Madrid on a nobleman who had been his patient. This autopsy was carried out in front of a large crowd of citizens and when the thorax of the body was opened the heart was beating. After that Versalius was compelled to leave Spain. This and others episodes probably have made it necessary to have physicians pronounce the death of patients.

 

PREREQUISITES

The presence of sedative drugs, hypothermia, shock, or other potentially reversible conditions that may depress brain function must be excluded for these clinical criteria to be valid:

  1. Body temperature must be 32.2 degree (90 degree F) or higher.

  2. If barbiturates are present in the blood, or were used therapeutically for control of intracranial pressure or seizures, serum levels should not exceed 1 mg % at the time of the clinical examination.

  3. Screen to exclude other sedative drugs-where clinically indicated.

  4. Absence of severe hypotension (shock).

CLINICAL CRITERIA

The clinical examination should be done by a neurologist, neurosurgeon, or critical care attending who is familiar with the neurological examination and with these criteria:

  1. Coma with cerebral unresponsitivity

  2. Apnea

  3. Absent brain stem reflexes

  4. Persistence of condition for 6 to 24 hours

  1. Unresponsive Coma

The patient should be deeply comatose with no movements, no withdrawal, seizures, or posturing (decerebrate or decorticate), spontaneously or to noxious stimulation. There may be spinal cord reflexes.

 

  1. Apnea

Apnea may be demonstrated by the absence of spontaneous respiration in the presence of an adequate carbon dioxide (CO2) drive.

The apnea test is a clinical bedside test to determine the response of the medullary brain stem respiratory center to a CO2 stimulus. In the absence of significant pulmonary disease or neuromuscular paralysis, a lack of respiratory effort to hypercarbia implies destruction of the most caudal part of the brain stem.

The test is begun by pre-oxygenation with 100% oxygen via the ventilator for about 5 minutes. The ventilator is withdrawn and the trachea is cannulated with an oxygen catheter. A passive flow of 100% oxygen at 4 1/min allows the PCO2 to rise without hypoxia. A baseline arterial blood gas (ABG) is drawn to ensure that the PCO2 is normalized. Observe the patient's undraped chest and abdomen for respiratory effort. After 5 and l0 minutes an ABG is drawn and the patient returned to the ventilator. A pulse oximeter should be used.

If in the presence of a negative drug screen and in the absence of metabolic intoxication, evidence of a paralyzing disease (e.g. Guillan-Barre, Myesthenia Gravis), or of neuromuscular blockade, there is no respiratory effort after an arterial PCO2 of more than 60 mm Hg has been achieved, the patient is apneic. Usually an ABG is drawn at baseline, 5 and 10 minutes.

The apnea test is done near the end of the period of observation. Patients whose PO2 cannot be maintained at normal levels may be excluded from a formal, apnea test.

Recommended Procedure

    1. Prerequisites:

      1. Core temperature should be at least 90°F (32.2o C).

      2. The patient should be hemodynamically stable.

      3. A baseline ABG has been obtained and the results show that the PaO2 is greater than 80, or O2 saturation is at least 95% and the PCO2 in 35-45mmHg.

      4. If the patient has a history of COPD or other chronic pulmonary disease, a pulmonary consult may be obtained.

      5. If the patient has received medications which may interfere with apnea testing, consultation with a neurologist, a neurosurgeon, an anesthesiologist, or a toxicologist may be sought. If there is any question concerning narcotic toxicity, a narcotic antagonist should be given.

    1. Equipment and Personnel:

      1. Suction catheter of appropriate size with connecting tubing

      2. Sterile gloves

      3. Oxygen or suction connecting tubing

      4. Oxygen flow meter with nipple

      5. ABG kits, pulse oximeter

      6. Cardiac monitor

      7. Nursing and respiratory therapy personnel may be of assistance in performing the procedure

    1. Suction the patient according to the standard procedure.

    2. Pre-oxygenate the patient with 100% oxygen on present means of respiratory support for five minutes.

    3. Remove patient from the ventilator (if possible); observe the time the test is started.

    4. Insert catheter into the endotracheal or tracheostomy tube. Care must be taken not to intubate a mainstem bronchus; the tip of the catheter should be at, or a few millimeters below, the tip of the endotracheal or tracheostomy tube.

    5. Attach the aspirator manifold of the catheter to the oxygen flow meter via the oxygen connecting tubing. Tape over the aspirator manifold port or occlude it with your thumb throughout the remainder of the procedure.

    6. Set the flow meter for 4 lpm. Monitor SaO2 by pulse oximeter.

    7. It is suggested that starting PaCO2 be 35-45 Torr. The PaCO2 will be allowed to rise while the undraped thorax and abdomen are observed and palpated carefully for signs of spontaneous respirations.

    8. An ABG should be drawn at approx. 5 minutes and 10 minutes of elapsed time to establish that the PaCO2 has reached 60mm Hg.

    9. If there are any respirations or if there is a loss of vital signs or oxygen desaturation below 90%, draw ABG and discontinue the test immediately. Reconnect the patient to ventilatory support after 10 hyperinflating breaths with the resuscitation bag using 100% oxygen.

    10. The test is over after approximately 10 minutes. If there is no respiratory effort after an arterial PCO2 of more than 60mm Hg has been achieved, the patient is apneic. Repeat testing for a period of time longer than 10 minutes may be required if PaCO2 is below 60 at the end of this test.

    11. Discontinue the test by hyperinflating with a resuscitation bag on 100% oxygen for a brief period until the patient's vital signs are stable and his/her color is normal. Resume pre-test ventilation.

It is recognized that on some occasions departure from the above procedures may be necessary. The reasons for such departure, if taken, should be documented in the patient's record.

 

  1. Absent Brain Stem Reflexes

    1. Pupils - should be mid position in size (4 mm) or dilated in the absence of mydriatics and unreactive to bright light or noxious stimulation.

    2. Eye movements - there should be no spontaneous eye movements, and the eyes should remain in the neutral position on testing the occulocephalic and occulovestibular reflexes. The occulocephalic response is tested by rapid rotation of the head to either side. In eliciting the occulovestibular reflex, 20-30 ml of ice water are instilled into each ear external auditory canal with an intact tympanic membrane with the head elevated 30 degrees.

    3. Corneal Reflex - No blinking or eye movement when the cornea is touched lightly with cotton.

    4. Gag Reflex - No gagging or coughing when the oropharynx or trachea is stimulated.

    5. Caloric testing

                  

                  Head is at 30° from horizontal

                        Brings horizontal semicircular canal into vertical and position of maximal sensitivity

                        Each auditory canal stimulated for 30 sec at temp of 30° and 44°C (7° above & below body temp) with 5 minutes between each irrigation

Cold stimulation: ipsilateral tonic deviation with nystagmus away

Warm stimulation: nystagmus towards side of stimulation.

Bilateral cold stimulation:              tonic downward deviation with nystagmus upward

Bilateral warm stimulation:         tonic upward deviation with nystagmus downward.

 

The presence of deep tendon or other spinal reflexes does not preclude the diagnosis of brain death.

 

  1. Duration of Observation

The clinical examination may be repeated after 12-24 hours. When there is a structural brain damage and the diagnosis is known with certainty, a shorter period of observation is adequate if central nervous system depressant drugs, metabolic and anoxic causes have been excluded.

 

5. Confirmatory Tests for Determination of Brain Death
 Although confirmatory tests are not mandatory in most situations, additional testing (Table 5) may be necessary for declaring brain death in patients in whom the results of specific components of clinical testing cannot be reliably evaluated.13 Clinical experience with confirmatory tests other than conventional angiography, lectroencephalography, and transcranial Doppler sonography is limited. Research involving use of confirmatory tests for determination of brain death is constrained by lack of blinded evaluation, absence of interobserver reliability data, and sparse use of control groups.

 



 Conventional Cerebral Angiography
 Selective 4-vessel angiography may be performed in the neuroradiology department. In patients with brain death, intracerebral filling is absent at the level of the carotid bifurcation or circle of Willis, whereas the external carotid circulation is patent13 (Figure 3).



 Electroencephalography
A 16- or 18-channel instrument and guidelines developed by the American Electroencephalographic Society are used to determine brain death.22,23 In patients with brain death, no electrical activity occurs during a period of at least 30 minutes of electroencephalographic recording.13

 Transcranial Doppler Sonography
In transcranial Doppler sonography, intracranial arteries are insonated bilaterally (ie, middle cerebral artery through the temporal bone above the zygomatic arch). Ten percent of patients may not have temporal insonation windows. Therefore, initial absence of Doppler signals cannot be interpreted as consistent with brain death. Findings consistent with brain death indicate high vascular resistance associated with greatly increased intracranial pressure and include (1) absent diastolic or reverberating flow, (2) systolic-only flow or retrograde diastolic flow, and (3) small systolic peaks in early systole. Blood flow velocities may be influenced by marked changes in Pco2, hematocrit, and cardiac output.12,13,24-27

 Somatosensory and Brain Stem Auditory Evoked Potentials
Testing for somatosensory evoked potentials is done at the bedside with a portable instrument that provides bilateral stimulation of median nerves. In studies13,28-31 of patients with brain death, most patients had no responses to tests for somatosensory and brain stem auditory evoked potentials. Both types of tests are less sensitive than previously mentioned confirmatory tests.

 Cerebral Blood Flow and Magnetic Resonance Imaging Studies
In one investigation,32 patients who met clinical criteria for brain death had no responses to tests for brain stem auditory evoked potentials and no cerebral perfusion as measured by radionuclide cerebral angiography and brain perfusion studies. Cerebral blood flow studies with xenon 133 have also been used to confirm brain death,33 and magnetic resonance imaging has been explored as a noninvasive method for determining the nonfilling phenomenon that occurs in brain death.34,35 In patients with brain death, technetium Tc 99m brain scans show no uptake of the radionuclide in brain parenchyma (“hollow skull phenomenon”).13

Neurophysiological technology and neurodiagnostic testing have great promise for becoming the gold standards for confirmatory tests of brain death. However, current investigations of technology-driven confirmatory tests still require further replication and clinical application.

 References
1. Practice parameters for determining brain death in adults: summary statement. Report of the Quality Standards Subcommittee of the American Academy of Neurology. In: Practice Handbook: American Academy of Neurology. St Paul, Minn: American Academy of Neurology; 1994.
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7. Taylor RM. Reexamining the definition and criteria of death. Semin Neurol. 1997;17:265-270.
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40. Medicare and Medicaid programs; hospital conditions of participation; provider agreements and supplier approval. 42 CFR Part 482. 62 Federal Register (1997).

 

 

 

1* Note: These guidelines have been developed to assist the physician in the determination of brain death in adults and in children 5 years and older. For children younger than 5 years of age, consultation with a pediatric neurologist or neurosurgeon should be obtained.

2* Guidelines for determination of death: Report of the medical consultants on the diagnosis of death to the President's Commission for the study of ethical problems in medicine and biomedical behavioral research. JAMA. 246:2184-2186. 1981