Potential reasons to pursue a formal diagnosis of brain death:. Is it worthwhile to pursue a formal brain death diagnosis? (2) Clinical examination consistent with brain death (described above đź“–). ⚠️ It's generally unwise to pursue the diagnosis of brain death in the absence of a known catastrophic injury compatible with brain death (e.g., if the CT scan doesn't show either herniation or severe cerebral edema). Common causes of brain death are listed above. For a patient with undifferentiated coma, brain death is a diagnosis of exclusion (e.g., only after alternative and treatable processes have been excluded). Brain death should primarily be considered within the context of known catastrophic brain injury. (1) Known catastrophic brain injury consistent with brain death. Initial suspicion of brain death involves roughly two components When in doubt, ancillary testing may be necessary to provide reassurance. If all other elements of the examination and neuroimaging are entirely consistent with brain death (e.g., CT scan showing herniation and failure to breathe during apnea test), reflexive-appearing movements are likely spinal reflexes. Sorting out spinal reflexes from intentional responses to stimuli may be very challenging, even for examiners who are experienced with brain death. The movement induced by a reflex is often precisely repeatable. Reflexes are often triggered by stimulation below the foramen magnum. Features that are consistent with spinal reflexes:. However, some patients may exhibit random twitching of facial muscles (myokimia), which is compatible with brain death if it is occurring spontaneously. Any grimacing in response to stimulation excludes brain death. đź’ˇPay particular attention to facial movement when applying noxious stimuli. Spinal reflexes should not occur with stimulation of the cranial nerves (e.g., painful stimuli at the supraorbital ridge or temporomandibular joint). Features that should never be seen with spinal reflexes:. This is often misinterpreted as representing volitional “withdrawal from pain.”Äifferentiating spinal reflexes from volitional movements The most classic spinal reflex is triple flexion, wherein stimulation of the feet causes flexion at the ankles, knees, and hips. This may closely mimic the appearance of someone who is responding to stimuli in a meaningful fashion. To complicate matters, spinal reflexes are often triggered by stimuli (e.g., painful stimuli below the diaphragm may lead to head turning). A list of described spinal reflexes is above. This may lead to some strange movements, which are often misinterpreted as intentional. Brain death leads to the disinhibition of spinal cord reflexes (which are normally suppressed). Unusual spinal reflexes are often observed in brain death Diabetes insipidus is commonly seen, but not always. Spinal reflexes may be seen – which can be confusing (more on this in the next section). ⚠️ Note, however, that various EEG artefacts can easily confuse this picture. If EEG is attached, it will be completely suppressed (totally flat EEG). Patient is not chemically paralyzed (e.g., deep tendon reflexes are preserved). A formal apnea test is still required before diagnosing brain death (more on this below đź“–). Alternatively, if the patient makes no respiratory effort despite a substantially elevated end tidal CO2, this suggests loss of respiratory drive. If the patient makes any respiratory effort, then they have an intact respiratory drive (so brain death is excluded). Observe the patient's vital signs, respiratory efforts, and end tidal CO2 for about five minutes. 
If safe, decrease the respiratory rate on the ventilator to a very low rate (e.g., 4 breaths/min). An informal apnea test may be used to provide more accurate information about whether the patient has an intact respiratory drive.⚠️ Note that if the ventilator's set respiratory rate is high enough to cause a respiratory alkalosis, which will normally suppress the patient's own respiratory drive.
(3) No respiratory drive (patient doesn't over-breathe the ventilator).No cough reflex (when suctioning endotracheal tube).(1) Coma (e.g., no cerebrally-mediated response to pain).Variety of drug intoxications, for example:.Ischemic stroke with cerebral edema and herniation.Fulminant hepatic failure causing cerebral edema.Anoxic brain injury (usually due to cardiopulmonary arrest).(1) common causes of brain death (if present, these support the diagnosis of brain death)
Be extremely cautious about pursuing a diagnosis of brain death in patients who lack an underlying process that explains why they should be brain dead. Clinical context may either support the possibility of brain death, or it may suggest the possibility of a brain-death mimic.
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