Brain Stem is where the cerebrum may be intact, though cut off functionally by the stem lesion. The loss of the vital centers that control respiration, and of the ascending reticular activating system that sustains consciousness, cause the victim to be irreversibly comatose and incapable of spontaneous breathing. This can be produced by raised intracranial pressure, cerebral edema, intracranial hemorrhage, etc.
The tissue in the floor of the aqueduct, between the third and fourth ventricles of the brain contains ascending reticular activating system. The ascending reticular activating substance, which extends throughout the brain-stem from the spinal cord to the subthalamus, determines arousal.
Damage to the ascending reticular activating substance or damage to areas of the cerebral hemispheres results in disturbance of normal consciousness. If this area is dead, the person is irreversibly unconscious and apnoeic (incapable of breathing).
Functions of Brain stem
A properly functioning paramedian segmental area of the brain stem is a precondition for full consciousness which enables the cerebral hemispheres to work in an integrated way. Lesions of this part are associated with profound coma.
The brainstem is also responsible for the respiratory drive, and in large measure (but not exclusively) for the maintenance of blood pressure. All motor output from the brain travel through the brainstem. Apart from vision and smell, all the sensory traffic coming into the brain arrives through the brain stem. The brain stem also mediates the cranial nerve reflexes.
Philadelphia Protocol (1969)
It determined death on the basis of
(1) Lack of responsiveness to internal and external environment.
(2) Absence of spontaneous breathing movements for 3 minutes, in the absence of hypocarbia and while breathing room air.
(3) No muscular movements with generalized flaccidity and no evidence of postural activity or shivering.
(4) Reflexes and responses: (a) Pupils fixed, dilated, and nonreactive to strong stimuli, (b) Absence of corneal reflexes. (c)Supraorbital or other pressure responses absent (both pain response and decerebrate posturing). (d) Absence of snouting and sucking responses. (e) No reflex response to upper and lower airway stimulation. (I) No ocular response to ice-water stimulation of inner ear. (g) No superficial and deep tendon reflexes. (h) No plantar responses.
(5) Failing arterial pressure without support by drugs or other means.
(6) Isoelectric EEG (in the absence of hypothermia, anesthetic deaths, and drug intoxication) recorded spontaneously and during auditory and tactile stimulation.
These criteria shall have been present for at least 2 hours and two physicians other than the physician of a potential organ recipient should certify death. As the protocol insists on a two hour delay, this precludes the use of any organs for transplantation.
Minnesota Criteria (1971)
The criteria for brain stem death was formulated by Mohan Dass and Chou as follows:
(1) Known but irreparable intracranial lesion.
(2) No spontaneous movement.
(3) Apnoea when tested for a period of 4 minutes at a time.
(4) Absence of brain stem reflexes : (a) dilated and fixed pupils, (b) absent corneal reflexes, (c) absent Doll’s head phenomenon, (d) absent ciliospinal reflexes, (e) absent gag reflex, (f) absent vestibular response to caloric stimulation, (g) absent tonic neck reflex,
(5) EEG not mandatory.
(6) Spinal reflex not important.
(7) All the findings above remain unchanged for at least 12 hours.
Brain stem death can be pronounced only if the pathological process responsible for states (1) to (4) above are deemed irreparable with presently available means.
Harvard Criteria
Unreceptivity and unresponsivity – Total unawareness to externally applied stimuli and inner need and complete unresponsiveness to even the most intense painful stimuli.
No movements – No spontaneous muscular movements in response to stimuli such as pain, touch, sound or light for a period of at least one hour.
Apnoea – Absence of spontaneous breathing for at least one hour and when patient is on ventilator, the total absence of spontaneous breathing may be established by turning off the respirator for 3 minutes and observing whether there is any effort on the part of the subject to breathe spontaneously.
Absence of elicitable reflexes – Irreversible coma with abolition of central nervous system activity is evidenced in part by the absence of elicitable reflexes. The pupils are fixed and dilated and do not respond to a direct source of bright light. Ocular movement and blinking are absent. There is no evidence of postural activity. Corneal and pharyngeal reflexes are also absent. Stretch tendon reflexes also cannot be elicited.
Isoelectric EEG: It has confirmatory value. All these tests should be repeated after 24 hours with no change. Further it is stressed that the patient be declared dead before any effort is made to take him off the ventilator, if he is then on a ventilator. This declaration should not be delayed until he has been taken off the respirator and all artificially stimulated signs have ceased.
There are two distinct schools of diagnosing death:
(1) French and English schools that are similar to Harvard.
(2) Austro-German school that includes Harvard criteria and bilateral serial angiography of internal carotid and vertebral artery criteria. A negative angiogram for more than 15 minutes proves death.
Diagnosis of Brain stem Death: Exclusions
(1) Where the patient may be under the effects of drugs, e.g. therapeutic drugs or overdoses. (2) Where the core temperature of the body is below 35°C. (3) Where the patient is suffering from severe metabolic or endocrine disturbances which may lead to severe but reversible coma, e.g. diabetes.
Preconditions of diagnosis:
(i) Patient must be deeply comatose.
(ii) Patient must be maintained on a ventilator.
(iii) Cause of the coma must be known.
Personnel who should perform the tests:
(1) Brain stem death tests must be performed by two medical practitioners.
(2) Doctors involved should be experts in this field. Under no circumstances are brain stem death tests performed by transplant surgeons.
(3) At least one of the doctors should be of consultant status. Junior doctors are not permitted to perform these tests.
(4) Each doctor should perform the tests twice.
Tests to be performed
Before the tests are performed the core temperature of the body is taken to ensure that it is above 35°C. The diagnosis of brain stem death is established by testing the function of the cranial nerves which pass through the brain stem. If there is no response to these tests, the brain stem is considered to be irreversibly dead:
(1) Pupils are fixed in diameter and do not respond to changes in the intensity of light.
(2) There is no corneal reflex.
(3) Vestibulo-ocular reflexes are absent, i.e. no eye movement occurs after the instillation of cold water into the outer ears.
(4) No motor responses within the cranial nerve distribution can be elicited by painful or other sensory stimuli, that is the patient does not grimace in response to a painful stimulus.
(5) There is no gag reflex to bronchial stimulation by a suction catheter passed down the trachea.
(6) No respiratory movements occur when the patient is disconnected from the ventilator for long enough to ensure that the carbon dioxide concentration in the blood rises above the threshold for stimulating respiration, i.e. after giving the patient 100% oxygen for 5 minutes. If no spontaneous breathing of any sort occurs within that 10 minutes, the brain stem is incapable of reacting to the presence of the carbon dioxide and is thus dead.
When two doctors have performed these tests twice with negative results, the patient is pronounced dead and a death certificate can be issued.
Whole or part of the brain can be irreversibly damaged due to hypoxia, cardiac arrest, intracranial hemorrhage, poisoning and trauma to it. If the cortex alone is damaged, the patient passes into deep coma, but the brain stem will function to maintain spontaneous respiration.
This is called “persistent vegetative state” and death may occur months or years later due to extension of cerebral damage or from inter current infection. They are not in need of life- sustaining treatment but require nutrition and hydration.
If the brain stem is damaged due to trauma, cerebral edema, hemorrhage, hypoxia or infection, such as poliomyelitis, respiratory motor system fails and damage to the ascending reticular activating system causes permanent loss of consciousness, and higher centers in the cortex are also irreversibly damaged causing ‘whole brain death’.
Tissue and organ transplantation:
(1) Homologous donation means grafting of the tissue from one part of the body to another in the same patient, such as skin or bone.
(2) Live donation includes blood and bone marrow transfusion. Live organ donation include kidney and parts of the liver.
(3) Cadaveric donation: Most organs must be obtained while the donor heart is still beating to improve chances of success.
Xenograft is grafting of animal tissue into humans, which has limited success. Zoonoses are transmission of animal diseases.
STUPOR: The patient appears to be asleep and shows little or no spontaneous activity, responding only to vigorous stimulation and then lapsing back into somnolence.
VEGETATIVE STATE: In this the patient breathes spontaneously, has a stable circulation and shows cycles of eye opening and closing which may simulate sleep and waking, but is unaware of the self and the environment. Commonest causes are diffuse axonal injury and diffuse ischemic brain damage. There is widespread bilateral damage to the neocortex, diffuse damage to white matter, and bilateral damage to the thalami.
THE BEATING-HEART DONOR: After brain stem death has been established, the retention of the patient on the ventilator facilitates a fully oxygenated cadaver transplant, the so-called “beating-heart donor”. The results of the transplant are much improved. This has no legal sanction.
MOLECULAR DEATH: It means the death of cells and tissues individually, which takes place usually one to two hours after the stoppage of the vital functions. Molecular death occurs piecemeal. Individual cells will live on their residual oxygen for a variable time after the circulation has stopped, depending on the metabolic activity of the cell.
The subsequent changes occur due to metabolic dysfunction and later from structural disintegration. Nervous tissues die rapidly, the vital centers of the brain in about five minutes, but the muscles live up to one to two hours.
