Brain death is defined as an irreversible loss of all functions of the brain, including the brainstem.The brainstem is a critical part of the human brain. It connects the spinal cord to the rest of the brain and controls the flow of messages between the brain and the rest of the body. It also controls basic and vital functions such as breathing, swallowing, heart rate, blood pressure, consciousness and wakefulness.
Brain death criteria:
For a person to be considered brain dead, three key criteria should be met.
b) Absence of brain stem reflexes
This is a prolonged state of unconsciousness due to a severe brain injury. The person is unresponsive to his environment and does not respond to any external stimulus, including deep pain.
Absence of brain stem reflexes
A reflex is an action that is performed without any conscious thought in response to a stimulus. In order to diagnose brain death, certain brain stem reflexes need to be tested to confirm that they are absent.The oculocephalic reflex is an automatic eye movement that stabilizes images during head movement. When the head moves in one direction, the eyes will move in the opposite direction so that the image of what is being seen is preserved. This reflex will be absent in a patient with brain death.Another reflex, known as the vestibulo-ocular reflex, is based on eye movement when a small amount of cold or warm water is poured in a ear. With cold water, the eyes will automatically move in the opposite direction and with warm water, they will move towards the side of the test. This reflex is also absent in brain death.Other absent brain stem reflexes include the pupillary reflex (where bright light will make the pupils in the eye smaller), corneal reflex, cough and gag reflexes.
This is defined as stoppage of external breathing, where there is no movement of the muscles that control breathing, such as the diaphragm and chest wall muscles.The apnea test looks for changes in the oxygen and carbon dioxide levels in the blood after the lungs are given oxygen through the ventilator. If there are no respiratory movements and if the oxygen level is low or if the carbon dioxide levels are high, this supports the diagnosis of brain death.
Diagnosis of brain death requires that a physician, usually a brain specialist evaluate the patient’s history and look at all the lab tests as well as the different xrays and CT scans to come to a conclusion that the person being examined is indeed brain dead.Once brain death is confirmed, the family is notified and they can then be given an opportunity to consider organ donation.
In some individuals, confirmatory testing is sometimes required to support the diagnosis of brain death.
These tests include:
a) Angiography, which is a study where a dye is injected into the blood stream and there is no demonstrable filling of the blood vessels to the brain, which supports the clinical diagnosis of brain death.
b) EEG, which is a test to record the electrical activity in the brain by attaching electrodes to the scalp. Documenting that there is no electrical activity during at least a 30 minute period confirms brain death.
c) Nuclear brain scan, where a radioactive dye is injected into the blood stream and shows no uptake in the brain, confirming brain death.
d) Somatosensory evoked potential, where electrical activity is measured in the brain in response to stimulation of a nerve in the arm, known as the median nerve, which shows an absence when both arms are tested in brain dead individuals.
e) Transcranial Doppler ultrasound, which is a special machine that tests the flow of blood gong in and then out of the brain. Brain death is confirmed when very high pressures are recorded.
When organ donation is being considered, certain states require that two physicians, neither of whom are part of the transplant team, independently certify that the individual meets all the criteria of brain death. This ensures a fair and unbiased process without any influence of extraneous factors when making this diagnosis.