Brain death

Irreversible loss of all brain function clinically demonstrates brain stem areflexia, and apnea.

Refers  to the complete loss of brain function, including involuntary activity necessary to sustain life.

Brain death, according to neurologic criteria, accounts are approximately 2% of adult and 5% of pediatric in hospital deaths in the United States.

Brain death is a direct byproduct of the invention of mechanical ventilation:as previously a patient with a neurologic catastrophe would become apneic with subsequent hypoxemia and the heart would stop beating shortly thereafter.

The legal basis for brain death is described as irreversible cessation of all functions of the entire brain, including the brain stem.

 

In a persistent vegetative state, the person is alive and some autonomic functions remain.

 

 

With ordinary coma some brain and bodily activity and function remain.

 

 

BD is an indicator of legal death in many jurisdictions.

 

 

Its definition is inconsistent and often confusing.

 

 

Brain death includes cerebral and brainstem death.

 

 

Someone with a dead cerebrum but a living brainstem, can have spontaneous breathing unaided, whereas in whole-brain death, only life support equipment would maintain ventilation. 

 

 

Patients classified as brain-dead can have their organs surgically removed for organ donation.

 

 

Brain death is an acceptable indication of death. 

 

 

The  legal and medical communities in the US use brain death as a legal definition of death, allowing a person to be declared legally dead even if life support equipment keeps the body’s metabolic processes working.

 

 

There  must be definite clinical or neuro-imaging evidence of acute brain pathology consistent with the irreversible loss of neurological function.

 

 

With brain-death there are no clinical evidences of brain function upon physical examination: no response to pain, no cranial nerve reflexes, no 

 

pupillary response, no oculocephalic reflex, no corneal reflex, no response to the caloric reflex test, and no spontaneous respirations.

 

 

With brain-death brain electrical activity can stop completely, or drop to such a low level as to be undetectable with most equipment: an EEG will be flat.

 

 

A flat EEG is not required to certify death.

 

 

A radionuclide cerebral blood flow scan that shows complete absence of intracranial blood flow must be considered with other exams

 

 

CT angiography is neither required nor sufficient test to make the diagnosis.

 

 

Cerebral angiography is considered the most sensitive confirmatory test in the determination of brain death.

 

 

Then diagnosis of brain death is the basis for the certification of death for legal purposes, but a very different state from biological death.

 

 

Continuing function of vital organs in the bodies of those diagnosed brain dead, provides optimal opportunities for their transplantation.

 

 

 

There is no evidence of arousal or awareness to maximal external stimulation, including noxious visual, auditory, and tactile stimulation, pupils are fixed in midsize or dilated position and are non-reactive to light, corneal, oculocephalic, and ocular vestibular reflexes are absent, there are no facial movement to noxious stimulation, the gag reflex is absent to bilateral posterior to pharyngeal stimulation, cough reflex is absent to deep tracheal suctioning, there is no brain mediated motor response to noxious stimulation of the limbs, spontaneous respirations are not observed when apnea test targets reach pH less than 7.3 and PaCO2 60 mmHg or greater.

Brain death involves the permanent and complete absence of human brain function.

Brain death involves the loss of function both the cerebrum, and the brain stem?

In assessing a patient before death of the brain is considered the patient must have a normal core body temperature because hypothermia can make it difficult to perform such an evaluation.

Sedative or paralyzing drugs can interfere with assessment of coma.

Very low blood pressure or severe abnormalities in blood glucose or other blood electrolytes need to be corrected before brain death assessment can be achieved.

Brain stem function is assessed by testing multiple reflexes: pupil responsiveness to light and coughing or gagging with throat suctioning.

Brain death can occur by a cerebral insult that is primary-subarachnoid hemorrhage, traumatic brain injury, intracerebral hemorrhage, massive ischemic stroke, or, in rare instances cerebral neoplasm: or secondary most common due to cardiac arrest with global anoxic brain injury.

regardless of the cause of brain death, the final common pathway is associated with increases in intracranial pressure leading to compromising cerebral circulation, secondary anoxic brain injury; with the process being completed when intracranial pressure exceeds the mean arterial pressure, and cerebral circulatory arrest ensues.

The loss of brain function typically progresses from rostral to caudal, with the loss of the brainstem functioning occurring last as it is relatively resilient to anoxic injury.

Within the brainstem, the medulla is the last to stop functioning, and it is reflected in the loss of respiratory drive.

The apnea test family temporarily removes the patient from mechanical ventilator and observes for a spontaneous breaths: if after 10 minutes no breathing is witnessed in the blood carbon dioxide level increases by 20 mmHg or more, the patient meets criteria for brain death.

Before concluding brain death is present it must be assured that the absolute irreversibility of the condition exists.

When establishing irreversibility there is a waiting period, and in the case of global anoxic brain injury after cardiac arrest a minimum waiting period of at least 24 hours is standard.

Clinical examination for the determination of brain death requires maximal stimulation to establish coma by the absence of responsiveness to all noxious stimuli including auditory, visual, and tactile stimulation.

Pressure on examination should be applied to the trunk, arms, legs, supraorbital notch, and the temporomandibular joint.

The detection of a pupillary reaction precludes determination of brain death.

Adequate corneal reflex should be tested with adequate stimulation with light, direct application of pressure adjacent to the iris.

Ocular vestibular or caloric reflex tests should be performed.

The apnea test assesses the function of the medulla by allowing carbon dioxide levels to rise in the pH to fall to maximally stimulate medullary respiratory centers, and in the absence of respiratory effort in response to hypercarbia and acidosis is consistent with brain death.

The apnea test is performed after all of the clinical testing is consistent with brain death.

This test is performed when the ventilator is temporarily disconnected.

EEG was traditionally used as an ancillary test for brain death is generally now considered not to be useful in determining brain death, given its false positive and false negative results.

Testing of cerebral perfusion is the preferred method of ancillary testing, as evidence of cerebral blood flow precludes diagnosis of brain death.

Doppler ultrasound is the most excepted means of determining brain death.