Neurologic Criteria for Death (Brain Death Testing)
New guidelines form AAN (Neurology 2010;74:1911)
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PRACTICAL (NON-EVIDENCE-BASED) GUIDANCE FOR DETERMINATION OF BRAIN DEATH
Many of the details of the clinical neurologic examination to determine brain death cannot be established by evidence-based methods. The detailed brain death evaluation protocol that follows is intended as a useful tool for clinicians. It must be emphasized that this guidance is opinion-based. Alternative protocols may be equally informative.
The determination of brain death can be considered to consist of 4 steps.
I. The clinical evaluation (prerequisites).
A. Establish irreversible and proximate cause of coma.The cause of coma can usually be established by history, examination, neuroimaging, and laboratory tests.Exclude the presence of a CNS-depressant drug effect by history, drug screen, calculation of clearance using 5 times the drug’s half-life (assuming normal hepatic and renal function), or, if available, drug plasma levels below the therapeutic range. Prior use of hypothermia (e.g., after cardiopulmonary resuscitation for cardiac arrest) may delay drug metabolism. The legal alcohol limit for driving (blood alcohol content 0.08%) is a practical threshold below which an examination to determine brain death could reasonably proceed.There should be no recent administration or continued presence of neuromuscular blocking agents (this can be defined by the presence of a train of 4 twitches with maximal ulnar nerve stimulation).There should be no severe electrolyte, acid-base, or endocrine disturbance (defined by severe acidosis or laboratory values markedly deviated from the norm).
B. Achieve normal core temperature.In most patients, a warming blanket is needed to raise the body temperature and maintain a normal or near-normal temperature (>36°C). After the initial equilibration of arterial CO2 with mixed central venous CO2, the Paco2 rises steeply, but then more slowly when the body metabolism raises Paco2.To avoid delaying an increase in Paco2, normal or near-normal core temperature is preferred during the apnea test.
C. Achieve normal systolic blood pressure.Hypotension from loss of peripheral vascular tone or hypovolemia (diabetes insipidus) is common; vasopressors or vasopressin are often required. Neurologic examination is usually reliable with a systolic blood pressure >=100 mm Hg.
D. Perform 1 neurologic examination (sufficient to pronounce brain death in most US states).If a certain period of time has passed since the onset of the brain insult to exclude the possibility of recovery (in practice, usually several hours), 1 neurologic examination should be sufficient to pronounce brain death. However, some US state statutes require 2 examinations.Legally, all physicians are allowed to determine brain death in most US states. Neurologists, neurosurgeons, and intensive care specialists may have specialized expertise. It seems reasonable to require that all physicians making a determination of brain death be intimately familiar with brain death criteria and have demonstrated competence in this complex examination. Brain death statutes in the United States differ by state and institution. Some US state or hospital guidelines require the examiner to have certain expertise.
II. The clinical evaluation (neurologic assessment).
* Patients must lack all evidence of responsiveness.Eye opening or eye movement to noxious stimuli is absent. Noxious stimuli should not produce a motor response other than spinally mediated reflexes. The clinical differentiation of spinal responses from retained motor responses associated with brain activity requires expertise.
B. Absence of brainstem reflexes.
- Absence of pupillary response to a bright light is documented in both eyes.Usually the pupils are fixed in a midsize or dilated position (49 mm). Constricted pupils suggest the possibility of drug intoxication. When uncertainty exists, a magnifying glass should be used.
- Absence of ocular movements using oculocephalic testing and oculovestibular reflex testing.Once the integrity of the cervical spine is ensured, the head is briskly rotated horizontally and vertically. There should be no movement of the eyes relative to head movement. The oculovestibular reflex is tested by irrigating each ear with ice water (caloric testing) after the patency of the external auditory canal is confirmed. The head is elevated to 30 degrees. Each external auditory canal is irrigated (1 ear at a time) with approximately 50 mL of ice water. Movement of the eyes should be absent during 1 minute of observation. Both sides are tested, with an interval of several minutes.
- Absence of corneal reflex.Absent corneal reflex is demonstrated by touching the cornea with a piece of tissue paper, a cotton swab, or squirts of water. No eyelid movement should be seen.
- Absence of facial muscle movement to a noxious stimulus.Deep pressure on the condyles at the level of the temporomandibular joints and deep pressure at the supraorbital ridge should produce no grimacing or facial muscle movement.
- Absence of the pharyngeal and tracheal reflexes.The pharyngeal or gag reflex is tested after stimulation of the posterior pharynx with a tongue blade or suction device. The tracheal reflex is most reliably tested by examining the cough response to tracheal suctioning. The catheter should be inserted into the trachea and advanced to the level of the carina followed by 1 or 2 suctioning passes.
* Absence of a breathing drive.Absence of a breathing drive is tested with a CO2 challenge. Documentation of an increase in Paco2 above normal levels is typical practice. It requires preparation before the test.Prerequisites: 1) normotension, 2) normothermia, 3) euvolemia, 4) eucapnia (Paco2 3545 mm Hg), 5) absence of hypoxia, and 6) no prior evidence of CO2 retention (i.e., chronic obstructive pulmonary disease, severe obesity).Procedure:
* Adjust vasopressors to a systolic blood pressure >=100 mm Hg. * Preoxygenate for at least 10 minutes with 100% oxygen to a Pao2 >200 mm Hg.
* Reduce ventilation frequency to 10 breaths per minute to eucapnia.
* Reduce positive end-expiratory pressure (PEEP) to 5 cm H2O (oxygen desaturation with decreasing PEEP may suggest difficulty with apnea testing).
* If pulse oximetry oxygen saturation remains >95%, obtain a baseline blood gas (Pao2, Paco2, pH, bicarbonate, base excess).
* Disconnect the patient from the ventilator.
* Preserve oxygenation (e.g., place an insufflation catheter through the endotracheal tube and close to the level of the carina and deliver 100% O2 at 6 L/min).
* Look closely for respiratory movements for 810 minutes. Respiration is defined as abdominal or chest excursions and may include a brief gasp.
* Abort if systolic blood pressure decreases to <90 mm Hg.
* Abort if oxygen saturation measured by pulse oximetry is <85% for >30 seconds. Retry procedure with T-piece, CPAP 10 cm H2O, and 100% O2 12 L/min.
* If no respiratory drive is observed, repeat blood gas (Pao2, Paco2, pH, bicarbonate, base excess) after approximately 8 minutes.
* If respiratory movements are absent and arterial Pco2 is >=60 mm Hg (or 20 mm Hg increase in arterial Pco2 over a baseline normal arterial Pco2), the apnea test result is positive (i.e., supports the clinical diagnosis of brain death).
* If the test is inconclusive but the patient is hemodynamically stable during the procedure, it may be repeated for a longer period of time (10-15 minutes) after the patient is again adequately preoxygenated.
How to Safely Perform Apnea Testing with CPAP: 6 L/min via a tracheal insufflation catheter, and 2) connected a 20 cm of H2O CPAP valve to the end of the endotracheal tube (APNEA TESTING FOR BRAIN DEATH IN SEVERE ACUTE RESPIRATORY DISTRESS SYNDROME: A POSSIBLE SOLUTION Hocker S; )
III. Ancillary tests.In clinical practice, EEG, cerebral angiography, nuclear scan, TCD, CTA, and MRI/MRA are currently used ancillary tests in adults (see appendix 1). Most hospitals will have the logistics in place to perform and interpret an EEG, nuclear scan, or cerebral angiogram, and these 3 tests may be considered the preferred tests. Ancillary tests can be used when uncertainty exists about the reliability of parts of the neurologic examination or when the apnea test cannot be performed. In some protocols, ancillary tests are used to shorten the duration of the observation period.The interpretation of each of these tests requires expertise. In adults, ancillary tests are not needed for the clinical diagnosis of brain death and cannot replace a neurologic examination. Physicians ordering ancillary tests should appreciate the disparities between tests and the potential for false-positives (i.e., the test suggests brain death, but the patient does not meet clinical criteria). Rather than ordering ancillary tests, physicians may decide not to proceed with the declaration of brain death if clinical findings are unreliable.
IV. Documentation.The time of brain death is documented in the medical records. Time of death is the time the arterial Pco2 reached the target value. In patients with an aborted apnea test, the time of death is when the ancillary test has been officially interpreted. A checklist is filled out, signed, and dated (appendix 2). Federal and state law requires the physician to contact an organ procurement organization following determination of brain death.e4,e5
CTA seems to be as good as formal angio for brain death (J Trauma 2010;68:553)
I take the patient completely off the ventilator after sticking a small oxygen conduit (like a nasal O2 tube) down the E-T tube to provide oxygenation without ventilation. The pCO2 rises 4 torr the first minute and 3 torr every minute thereafter. You know where the pCO2 started. Do the math. The pO2 maintains well over 200 for the entire 5 minutes or so it takes to get to a pCO2 of > 60. I’ve never had a sudden unexpected cardiac arrest with this procedure and I’ve been doing it for over 15 years. During that 5 minutes or so, i simply eyeball the patient. If they show any hint of movement of any kind, they instantly flunk and the brain death test is over. If they don’t make any kind of effort with a pCO2 over 60, that’s the end of the story.
The diagnosis of brain death (NEJM 2001;344(16):1215)
no reversible cause temp>32 normotension exam: coma absence of motor absence of pupillary response (should be 4-6mm) absence of calorics absence of gag absence of coughing to trach suction absence of resp drive atPaCo2 of 60 or 20 above baseline do calorics with head tilted to 30 degrees
unusual movements in the braindead (neurology 1984;34:1089)
apnea test-why not give pt CO2 instead of the miserable way we do it now (Neurocritical Care 2004;1:)
ANZICs guidelines including apnea test procedure
CPAP maintains oxygenation best (Crit Care Med 2006;34(8):2213)
used cont. flow CPAP with the addition of 10 cm PEEP valve attached to distal extremity of T piece
This set-up from APNEA TESTING FOR BRAIN DEATH IN SEVERE ACUTE RESPIRATORY DISTRESS SYNDROME: A POSSIBLE SOLUTION Sara Hocker, MD1, Francis Whalen, MD2, Eelco F.M.Wijdicks MD, Ph.D1
may be the ideal solution
Apnea Testing During ECMO (Apnea test during brain death assessment in mechanically ventilated and ECMO patients Volume 42, Issue 1 / January , 2016 Pages 72 – 81)
From Stephen Streat:
Poikilothermia occurs in brain dead patients — they cannot maintain normal body temperature in the face of cooler envirnmental temperature. It is due to a combination of several factors — 1) Reduced heat production from brain (perhaps 20% of VO2/VCO2 is due to brain metabolism)2) Reduced heat production in other tissues (perhaps another 5% fall in energy expenditure) — due to probably two issues a) hormonal change and b) loss of resting muscle tone in skeletal muscle3) Vasoplegia (no ability to retain heat by vasoconstriction) — hence the “pink and warm” hands that are such a cruel verisimilutude of “vitality”.4) No ability to shiver (the brain is dead remember) to generate heat to compensate for a fall in body temperature (the afferents don’t go anywhere, the processor is out of action and the efferents don’t connect up either). It is very easy to prevent hypothermia developing during brain death, but much harder to reverse it once it happens — you have to add an external heat source and not rely on “endogenous heat production”. To prevent it you must anticipate it and insulate the patient well, control diabetes insipidus quickly (prevent the loss of warm urine) and avoid cold IV fluids going in. They do this well even in Invercargill (southernmost city, after which there be only penguins).Back to top