let me tell u somethings abt brain dead

Brain death is a legal definition of death that emerged in the 1960s as a response to the ability to resuscitate individuals and mechanically keep the heart and lungs working. In simple terms, brain death is the irreversible end of all brain activity (including involuntary activity necessary to sustain life) due to total necrosis of the cerebral neurons following loss of blood flow and oxygenation. It should not be confused with a persistent vegetative state.

Traditionally, both the legal and medical communities determined death through the end of certain bodily functions, especially respiration and heartbeat. With the increasing ability of the medical community to resuscitate people with no heart beat, respiration or other signs of life, the need for a better definition of death became obvious. This need gained greater urgency with the widespread use of life support equipment, which can maintain body functions indefinitely, as well as rising capabilities and demand for organ transplantation.

Today, both the legal and medical communities use "brain death" as a legal definition of death. Using brain-death criteria, the medical community can declare a person legally dead even if life support equipment keeps the body's metabolic processes working. The first nation to adopt brain death as a legal definition of death was Finland in 1971. In the United States, Kansas enacted a similar law earlier.[1]

A brain-dead individual has no clinical evidence of brain function upon physical examination. This includes no response to pain and no cranial nerve reflexes. Reflexes include pupillary response (fixed pupils), oculocephalic reflex, corneal reflex, no response to the caloric reflex test and no spontaneous respirations.
It is important to distinguish between brain death and states that may mimic brain death (e.g., barbiturate intoxication, alcohol intoxication, sedative overdose, hypothermia, hypoglycemia, coma or chronic vegetative states). Some comatose patients can recover, and some patients with severe irreversible neurologic dysfunction will nonetheless retain some lower brain functions such as spontaneous respiration, despite the losses of both cortex and brainstem functionality. Thus, anencephaly, in which there is no higher brain present, is generally not considered brain death, though it is certainly an irreversible condition in which it may be appropriate to withdraw life support.
Note that brain electrical activity can stop completely, or drop to such a low level as to be undetectable with most equipment. This includes a flat EEG during deep anaesthesia or cardiac arrest. However, the EEG is not required in the United States, but is considered to have confirmatory value.
The diagnosis of brain death needs to be rigorous to determine whether the condition is irreversible. Legal criteria vary, but it generally requires neurological exams by two independent physicians. The exams must show complete absence of brain function, and may include two isoelectric (flat-line) EEGs 24 hours apart. The widely-adopted Uniform Determination of Death Act in the United States attempts to standardize criteria. The patient should have a normal temperature and be free of drugs that can suppress brain activity if the diagnosis is to be made on EEG criteria.
Alternatively, a radionuclide cerebral blood flow scan that shows complete absence of intracranial blood flow can be used to confirm the diagnosis without performing EEGs.

Medical science argues that a permanent cessation of electrical activity indicates the end of consciousness. Those who view the neo-cortex of the brain as solely responsible for consciousness, however, argue that electrical activity there should be the only consideration when defining death. In many cases, especially when elevated intracranial pressure prevents blood flow into the brain, the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex. The case of Zach Dunlap, in which a man was declared brain dead but later recovered and remembers the doctors pronouncing him dead, [16] questions this presumption. However, since he was declared dead only a few hours after presentation, he did not yet meet the American Academy of Neurology's brain death criteria. [17] While Dunlap was being disconnected from life support four hours after the pronouncement, one of his cousins, Dan Coffin, who is also a nurse, found he was responsive to pain, demonstrating that he was alive, [18] so this example is questionable.

(quoted from wiki)

I. Diagnostic criteria for clinical diagnosis of brain death
A. Prerequisites. Brain death is the absence of clinical brain function when the proximate cause is known and demonstrably irreversible.
1. Clinical or neuroimaging evidence of an acute CNS catastrophe that is compatible with the clinical diagnosis of brain death
2. Exclusion of complicating medical conditions that may confound clinical assessment (no severe electrolyte, acid-base, or endocrine disturbance)
3. No drug intoxication or poisoning
4. Core temperature ≥ 32° C (90°F)
B. The three cardinal findings in brain death are coma or unresponsiveness, absence of brainstem reflexes, and apnea.
1. Coma or unresponsiveness--no cerebral motor response to pain in all extremities (nail-bed pressure and supraorbital pressure)
2. Absence of brainstem reflexes
a) Pupils
i. No response to bright light
ii. Size: midposition (4 mm) to dilated (9 mm)
b) Ocular movement
i. No oculocephalic reflex (testing only when no fracture or instability of the cervical spine is apparent)
ii. No deviation of the eyes to irrigation in each ear with 50 ml of cold water (allow 1 minute after injection and at least 5 minutes between testing on each side)
Brain Death Page 2
c) Facial sensation and facial motor response
i. No corneal reflex to touch with a throat swab
ii. No jaw reflex
iii. No grimacing to deep pressure on nail bed, supraorbital ridge, or temporomandibular joint
d) Pharyngeal and tracheal reflexes
i. No response after stimulation of the posterior pharynx with tongue blade
ii. No cough response to bronchial suctioning
3. Apnea--testing performed as follows:
a) Prerequisites
i. Core temperature ≥ 36.5°C or 97°F
ii. Systolic blood pressure ≥ 90 mm Hg
iii. Euvolemia. Option: positive fluid balance in the previous 6 hours
iv. Normal PCO2. Option: arterial PCO2 ≥ 40 mm Hg
v. Normal PO2 Option: preoxygenation to obtain arterial PO2 ≥ 200 mm Hg
b) Connect a pulse oximeter and disconnect the ventilator.
c) Deliver 100% O2, 6 l/min, into the trachea. Option: place a cannula at the level of the carina.
d) Look closely for respiratory movements (abdominal or chest excursions that produce adequate tidal volumes).
e) Measure arterial PO2, PCO2, and pH after approximately 8 minutes and reconnect the ventilator.
f) If respiratory movements are absent and arterial PCO2 is ≥ 60 mm Hg (option: 20 mm Hg increase in PCO2 over a baseline normal PCO2), the apnea test result is positive (ie, it supports the diagnosis of brain death).
g) If respiratory movements are observed, the apnea test result is negative (ie, it does not support the clinical diagnosis of brain death), and the test should be repeated.
h) Connect the ventilator if, during testing, the systolic blood pressure becomes ≤ 90 mm Hg or the pulse oximeter indicates significant oxygen desaturation and cardiac arrhythmias are present; immediately draw an arterial blood sample and analyze arterial blood gas. If PCO2 is ≥ 60 mm Hg or PCO2 increase is ≥ 20 mm Hg over baseline normal PCO2, the apnea test result is positive (it supports the clinical diagnosis of brain death); if PCO2 is <>