In PVS it is most or all of the cortex -the grey matter"- which is destroyed, not the brainstem. The vegetative patient, therefore, breathes spontaneously; the brainstem dead patient cannot breathe unaided.
The brainstem is the most primitive part of the brain, controlling basic life processes such as breathing, the heartbeat and the ability of the cerebral hemispheres to maintain consciousness. If the brainstem dies, the heart will stop within a few hours or days, even if the patient is mechanically ventilated. In a major study of more than 1000 such patients-diagnosed brainstem dead but kept on ventilators all the same, the heart stopped in every single case.
In the early years of intensive care medicine, life support was continued until the heart stopped. This was futile for the patient and it prolonged the agony for his or her relatives. So, as time went by, medical and nursing staff pressed for some means of resolving the plight of this small but sufficient group of patients.
At this time there was no legal definition of death. Hitherto, it had been diagnosed by irreversible cessation of breathing and the action of the heart. But this clearly could not apply to cases where the heart continued to beat. To answer this need, neuro surgeons, anaesthetists, and other medical specialists collaborated to draw up guidelines for diagnosing brainstem death. These incorporated simple tests, which could be carried out at the bedside. In establishing these criteria, the UK led the world in resolving a painful dilemma.
Today in Britain brainstem death tests are performed by two experienced doctors who are not involved in transplantation. As an additional safeguard the tests are repeated, usually within a few hours. The time of death is that at which the second set of tests is completed. It is at this point that the ventilator is disconnected if there is to be no donation.
Normally the question of donation will have been raised during the interval between the first and second set of tests. If donation is agreed, arrangements are made for the retrieval operation.
This is a difficult and poignant time for intensive care staff, who continue to care for the potential organ donor as much as they did before death was certified. Medically, their concern is to maintain oxygenation of their tissues, to carry out routine hygienic measures, to prevent infection and to correct any fluid or chemical balances which may arise. Normally the patient is taken to the theatre within a few hours.
In the case of the multi organ donor, where several organs are to be removed, two or three surgical teams may be called in from various transplant centres. The retrieval operation, which may take up to four hours, is carried out with the same care and precision as an operation on the living patient.
Brainstem death is a bewildering concept for many people confronted with a body which is still pink and warm and in which the heart is still seen to beat. Relatives often find it helpful to be able to see their loved ones at rest, after the retrieval operation, either in a side ward in the intensive care unit, or in the hospital's chapel of rest.
Deep coma and beyond
Deep coma may result form many different causes, including head injury, brain haemorrhage, poisoning by drugs or other substances, hypothermia, infection, illness which disrupts the body's chemistry or failure of the oxygen supply to the brain. Many comatose patients are treated in intensive care units, where life support systems offer the best chance of recovery. Sometimes the condition is reversible and the patient recovers fully. But there are some patients who never regain awareness; some of these are brainstem dead.
The phenomenon of brainstem death has arisen entirely as a consequence of using modern resuscitation and life support technology on patients who can no longer breathe spontaneously.
The brainstem-dead patient appears as if in sleep; occasional limb movements are due to lingering spinal reflexes. Since there is no hope of recovery, brainstem death tests may be carried out, enabling formal confirmation of the patient's death.
Or sometimes the heart stops before the tests take place and death is diagnosed in the traditional way. Not all patients who suffer brainstem death become organ donors. Some may be unsuitable on medical grounds; in other cases there may be no consent for donation.
The vegetative state
The persistent vegetative state (PVS) results from overwhelming damage to the cortex. So here it is the cortex which dies while the sturdier cells of the brainstem live on. Composed of right and left cerebral hemispheres, the cortex contains the so-called higher centres of the brain, responsible for thought and feeling and for the initiation of voluntary movement. PVS is unlike a true coma in that the eyes are open for some of the time and a sleep/waking cycle is established. But the patient remains unaware of his or her surroundings, makes no purposeful gestures and never speaks. The vegetative patient may survive indefinitely - sometimes for many years - in a condition, which many people regard as living death.
Tests for brainstem death
The following tests are performed only on patients known to have sustained irreversible damage to the brain stem- for instance, through head injury, haemorrhage, tumour or a failure of the oxygen supply to the brain. What are being tested are the various reflexes, which signal life in the brain stem:
-
Pupils do not respond to light
-
No blinking when the cornea is touched
-
No eye movement when ears irrigated with ice cold water
-
No gagging response to stimulus at back of throat
-
No response to pain
If all these reflexes are absent, the ventilator is disconnected briefly to see if the patient makes any spontaneous efforts to breathe unaided. The ventilator is then reconnected and the tests are repeated a few hours later. If there is the slightest sign of life in the brainstem, the tests are discontinued. But if both sets of tests confirm that the brainstem is no longer functioning, death is certified.
We are indebted to BODY for providing the content for this section
