Neurological examination is considered as the gold standard to diagnose brain death and therefore must be performed accurately [7] [8]. It is essential to document presence of apnea, absence of brainstem reflexes and coma. The brainstem reflexes are lost in a rostral-to-caudal direction, with the medulla oblongata to be the last one to cease functioning in the event of brain death. Medullary function usually lasts for several hours as other functions of the brainstem are being lost [9]. If the medulla oblongata does not cease functioning, administration of 1 mg atropine will cause tachycardia, tracheal suctioning will lead to cough reflex and the blood pressure will be normal. The depth of coma can be assessed based upon the motor response to a standardized pain stimulation, done by pressing on temporomandibular joint, supraorbital nerve or finger nail bed. Next step is the evaluation of brainstem reflexes, which if absent, should show mid dilated non reactive round/oval pupils on ocular exam with absence of oculocephalic reflex. Presence of a spinal injury makes the interpretation of oculocephalic reflex challenging.

• Pupillary Abnormality

  Other situations possibly requiring confirmatory testing include severe facial trauma where determination of brainstem reflexes will be difficult, pre-existing pupillary abnormalities, and patients with severe sleep apnea and/or pulmonary disease. [en.wikipedia.org]

  Other variables that are correlated with a poor outcome include an advanced age, pupillary abnormalities, and a low score on a test of motor responses 47. [doi.org]

• Fixed Pupils

  A 28-year-old man was admitted following a road traffic accident with a Glasgow Coma Score (GCS) of 3/15 and fixed pupils. [ncbi.nlm.nih.gov]

  Reflexes include pupillary response (fixed pupils), oculocephalic reflex, corneal reflex, no response to the caloric reflex test, and no spontaneous respirations. [en.wikipedia.org]

  Usually the pupils are fixed in a midsize or dilated position (4–9 mm). Constricted pupils suggest the possibility of drug intoxication. When uncertainty exists, a magnifying glass should be used. [neurology.org]

• Motor Symptoms

  We describe and show on videotape a brain-dead patient with rare motor movements. We suggest that fasciculations outlined in this study has to be accepted as motor symptoms in brain death patients. [ncbi.nlm.nih.gov]

• Myokymia

  These included single reports of facial myokymia, transient bilateral finger tremor, repetitive leg movements, ocular microtremor, and cyclical constriction and dilatation in light-fixed pupils. 16–21 One Class III study of 144 patients pronounced brain [neurology.org]

In order to diagnose a patient with brain death, the first step is to rule out potential influence of paralyzing or sedating agents. The possibility of self administration of such agents should also be considered. In case status epilepticus is suspected, an electroencephalogram (EEG) must be performed. Hypothermia, defined by a core body temperature  of < 35°C should be increased gradually to > 36°C. The patient should be routinely evaluated for 6-24 hours. Ocular examination, with emphasis on brainstem reflexes and apnea testing must be performed with every examination. If the absence of brainstem reflexes is noted, apnea test must be performed.

To reduce the chances of misdiagnosing an individual with brain death, several countries have made a second clinical examination as a mandatory requirement, despite the absence of any evidence suggesting a possible benefit with this practice. On the contrary, it has been demonstrated that this practice, in fact delays the diagnosis of brain death. To determine the cause of brain death, a computed tomography (CT) scan of the head may be performed to look for pathologies such as hemispheric lesions, edema, mass, or herniation of the brain. Evaluation of the cerebrospinal fluid (CSF) is diagnostic where a central nervous system (CNS) infection is suspected. 

The following tests are indicated when only one clinical examination is desired (in a scenario where organ procurement needs to be done for transplantation) or if the apnea test is not tolerable hemodynamically:

• EEG, that shows complete absence of brain activity despite intense somatosensory and/or audiovisual stimulation in the presence of brain death.
• CT Angiography (cerebral), that shows absence of intracranial filling at the level of entry of vertebral and carotid arteries into the skull [11] in the presence of brain death. 

The current recommendations state that confirmatory testing must be performed in all children less than one year of age [10]. Several countries across the world have made confirmatory testing compulsory. However, it is for the physician to decide the battery of tests to be performed in the United States, where most physicians prefer bedside testing. Cerebral angiography is the only required confirmatory test in Sweden. 

Determination of brain death

Prerequisites (all prerequisites should be met)

• Coma that is irreversible and the cause is known
• Neuroimaging that can explain the reason for coma
• Systolic blood pressure greater than 100 mmHg
• Mild hypothermia or normothermia with a core body temperature greater than 36°C
• Absence of any evidence that suggests influence of paralytic agents (electrical stimulation may be performed if any use of a paralytic agent is suspected or known)
• Absence of the influence of any drug that can lead to CNS depression (toxicology screening may be performed, and if the patient was administered barbiturates, the serum level must be below 10 μg/ml)
• Absence of acid-base, endocrine or electrolyte abnormality that may lead to obtundation
• Absence of spontaneous respirations

Examination (all findings must be present)

• Non-reactive pupils when exposed to bright light
• Absence of corneal reflex
• Absence of gag reflex
• Absence of oculovestibular reflex
• Absence of oculocephalic reflex
• Absence of facial movements when a painful stimulus is applied at the temporomandibular joint or the supraorbital nerve
• Absence of any motor response when a painful stimulus is applied to any of the four limbs (spinal reflexes may be present; all four limbs should be tested)

Apnea testing (all findings must be present)

• Patient should be hemodynamically stable
• Patient should have normocarbia (achieved by adjusting the ventilator settings)
• Patient must have PaO2 >200 mmHg prior to disconnecting the ventilator, which is achieved by pre-oxygenation using 100% FiO2 for at least ten minutes
• Patient must be well oxygenated, with a positive end expiratory pressure (PEEP) of 5 cms H2O
• Oxygenate the patient by using a suction catheter inserted to the level of carina at a rate of 6 L/min or by attaching a T-piece with continuous (CPAP) at 10 cm H2O
• Disconnect the ventilator 
• Absence of spontaneous respirations noted
• After 8-10 minutes, an arterial blood gas sample is drawn and the ventilator is connected again with the patient
• The PCO2 should be ≥60 mmHg or must increase by a minimum of 20 mmHg from normal baseline

Or:

• Apnea test aborted

There are several alternative methods to support a diagnosis of brain death, in case if the apnea test is not conclusive or there are limitations due to patient factors that will not allow a complete clinical examination. These include:

• Cerebral angiogram
• EEG
• HMPAO SPECT
• TCD

• Cervical Spine X-Ray

  A cervical spine X‐ray showed a Hangman’s fracture of C2 (fracture of the pedicle) with displacement and a likely traction injury to the spinal cord (Fig. 1 ). [bja.oxfordjournals.org]

• Isoelectric EEG

  An isoelectric EEG is not mandatory, but when used in conjunction with the clinical criteria for brain death, it provides confirmatory evidence of brain death. [clevelandclinic.org]

  EEG ( Ad Hoc Committee 1968 ). [medlink.com]

  One Class III study evaluated bispectral index monitoring in 54 patients and noted a gradual decline in bispectral index values to 0 in 9 patients, implicating isoelectric EEG. [neurology.org]

  EEG and CBF studies may not show abnormalities that are described in older patients. An observation period of 24 to 48 hours is recommended. If the EEG is isoelectric or if CBF is absent, the observational period can be shortened. [nature.com]

  There have been occasional reports of isoelectric EEGs in patients in a vegetative state 37,58,76,81,82. [doi.org]

• Flat-Line EEG

  An EEG will therefore be flat, though this is sometimes also observed during deep anesthesia or cardiac arrest. Although in the United States a flat EEG test is not required to certify death, it is considered to have confirmatory value. [en.wikipedia.org]

The criteria for diagnosing brain death are firm. Using the practice parameters published in 1995 by the AAN as a criteria for diagnosis, there is no data since 1995 that shows recovery of neurological deficits after a diagnosis of brain death was made [12].

The state of brain death is equivalent to the death of the person since it is irreversible. Once brain death is confirmed, all life support is withdrawn. It must be noted that as the whithdrawl of ventilatory support after brain death will result in terminal arrythmias and terminal apnea may provoke spinal reflexes, which should not be interpreted as signs of life. 

Traumatic brain injury and subarachnoid hemorrhage are the most important causes for brain death in adults [5]. Abuse is a common cause for brain death in children, others being asphyxia and motor vehicle collisions [6].

The epidemiology of brain death is in direct association with the epidemiology of the two main causes for brain death. namely traumatic brain injury and subarachnoid hemorrhage. Traumatic brain injury leads to almost 52,000 deaths every year in United States alone. Mortality rate is significantly lower in the patients that are hospitalized (6/100,000 persons) versus those who do not receive hospitalization (17/100,000 persons).

In order to maintain cerebral perfusion pressure, the arterial blood pressure increases in response to an elevated intracranial pressure. If the cerebral perfusion remains inadequate, pontine ischemia may develop leading to Cushing's reflex, consisting of bradycardia and hypertension. Ischemic injury rapidly progresses to involve other parts of the brain leading to an autonomic storm that is characterized by peripheral vasoconstriction, hypertension and tachycardia. It is frequently associated with an elevated amount of catecholamines in circulation and myocardial dysfunction (due to increased oxygen demand and arrythmias). During the hypertensive phase, the vasomotor nuclei in the brainstem suffer irreversible damage which leads to loss of sympathetic outflow and as a consequence, hypotension ensues.

Prevention of brain death is not possible, however, various steps can be taken to decrease the risk for the causes of brain death, most important of them being subarachnoid hemorrhage. Good control of blood pressure and smoking cessation may help decrease the risk of subarachnoid hemorrhage.

Brain death is the complete cessation of integrated functions of the cerebrum and brainstem and constitutes the death of person. This concept is accepted in both legal and cultural aspects throughout the world. The need to develop this concept arose because certain drugs and medical equipment like a ventilator could maintain basic functions of the body such as cardio-pulmonary activity for an indefinite period of time even after cessation of all brain activity. 

The Uniform Determination of Death Act (UDDA) was formed based off a report on "guidelines for determination of death" by the president's commission [1]. The act states:

"An individual who has sustained either 1. Irreversible cessation of circulatory and respiratory functions or 2. Irreversible cessation of all functions of the entire brain, including the brain stem, is dead. A determination of death must be made with accepted medical standards" [2].

In the year 1995, the American Academy of Neurology (AAN) put forth a practice parameter in order to outline the medically acceptable standards to determine brain death [3]. They stated that for diagnosing brain death, the patient must have absence of brainstem reflexes, apnea and in a state of coma for which the cause is known.

Inspite of the practice parameter made available by the AAN, there is significant variation in practice at different medical institutions. A study conducted in US hospitals identified the points of variations [4]. The most important points of variation were:

1. The number of examinations necessary
2. The prerequisites
3. The lowest acceptable body temperature

Brain activity is lost permanently in brain death. The patient loses the ability to breathe and perform other important functions, along with complete loss of capacity to think and be aware of surroundings. The patient will not respond to any stimulus. Once a diagnosis of brain death is made, no further treatment can be of any help and the patient is legally dead. 

Various advances in medical science can help maintain some vital functions like beating of the heart and breathing even after the brain stops working completely. However, even with the use of such devices and drugs, the organs will stop working eventually. 

Brain death is diagnosed based on a strict criteria. Some of these criteria are:

• The patient does not try to breathe
• The eyes are not reacting to light
• The patient shows no movement when specific reflexes and responses are checked

The doctors will also check certain reflexes elsewhere in the body to confirm brain death. The doctors will notify the next of kin about the diagnosis.

Doctors will not confirm a diagnosis of brain death until they check for and treat all problems that can possibly affect the brain function. These problems include, but are not limited to low blood pressure, low body temperature, abnormal levels of normally found substances in the blood, ingestion of toxic drugs and sedative overdose.

The above criteria are checked for at least one more time in 6-24 hours to confirm the presence of these criteria. Once the criteria have been confirmed two times, no further testing is needed and a diagnosis of brain death can be confirmed. In case if the diagnosis needs to be performed in a shorter time, the doctors may run certain tests to do so, thus eliminating the need to recheck the patient 6-24 hours later.

Individuals who have been diagnosed with brain death do not recover. Once the diagnosis is confirmed, all life supporting treatment is withdrawn. Family members may be allowed to be with the patient at the time of withdrawing life support. It is important to note that the patient might move his/her limbs or may even sit up when the device that assists in breathing is withdrawn.

1. Guidelines for the 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 biochemical and behavioral research. JAMA1981; 246:2184–2186.
2. Uniform Determination of Death Act, 12 uniform laws annotated 589 (West 1993 and West suppl 1997).
3. The Quality Standards Subcommittee of the American Academy of Neurology. Practice parameters for determining brain death in adults (summary statement). Neurology 1995; 45:1012–1014.
4. Greer DM, Varelas PN, Haque S, Wijdicks EFM. Variability of brain death determination guidelines in leading US neurologic institutions. Neurology 2008; 70:284–289.
5. Wijdicks EF. Determining brain death in adults. Neurology. 1995;45: 1003-11. 
6. Ashwal S, Schneider S. Brain death in children. Pediatric Neurology. 1987; 3: 5-11. 
7. The Quality Standards Subcommittee of the American Academy of Neurology. Practice parameters for determining brain death in adults. Neurology. 1995;45:1012-4. 
8. Van Norman GA. A matter of life and death: what every anesthesiologist should know about the medical, legal, and ethical aspects of declaring brain death. Anesthesiology. 1999; 91:275-87.
9. Wijdicks EFM, Atkinson JLD, Okazaki H. Isolated medulla oblongata function after severe traumatic brain injury. J Neurol Neurosurg Psychiatry. 2001; 70:127-9.
10. American Academy of Pediatrics Task Force on Brain Death in Children. Report of special task force: guidelines for the determination of brain death in children. Pediatrics. 1987; 80:298-300. 
11. Bradac GB, Simon RS. Angiography in brain death. Neuroradiology. 1974; 7:25-8
12. Wijdicks EF, Varelas PN, Gronseth GS, Greer DM. Evidence-based guideline update: determining brain death in adults: report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2010; 74:1911-8.