The concept of brain death is an important one in medicine; all doctors will have to confirm brain death at least once in their career, and probably many, many times. However, brain death is often difficult for those outside of the medical profession to understand; patients who are brain dead, if placed on ventilation, will still have beating hearts – a state that is synonymous with life to many. The important thing to realise is that it is the brain that controls practically all body functions, and if it is damaged beyond recovery, it is dead, irreplaceable, and the rest of the body can not survive without it.
The correct declaration of brain death is essential for patients who are on mechanical ventilators, and especially when there is the possibility of harvesting the patient's organs for transplant. These patients are being kept 'alive' by machines; and if the machines were to be turned off, they would die. And by 'die', I mean cease spontaneous breathing, resulting in hypoxia and leading to the eventual failure of the body's essential organs such as the heart, liver and kidneys. Brain death is "the irreversible loss of the capacity for consciousness combined with the irreversible loss of the capacity to breathe." (Kumar, Clark, 2005) However, not everyone on a ventilator is brain dead, and there have been instances where doctors have genuinely thought someone to be brain dead and were (thank-god) proved wrong in time.
It can be very difficult to explain to relatives the concept of brain death; it's an emotionally fraught time and, as far as they're concerned, their relative is lying there on the bed, alive. Yes, a machine is breathing for them, but they're breathing, their heart is beating, so they must still be alive. All they need is some time. They'll get better. Won't they?
The problem is that their brain is no longer functioning; the person that they love is no longer in there. Without the brain, the rest of the body is nothing but a machine. But the machine parts are a vital resource; transplant waiting lists are getting longer and longer, and while this patient has died, we still have the chance to allow others to live who might otherwise also die, and soon. Organ harvesting is not a pretty business, but it saves lives. If we didn't need to do it, we wouldn't, and it can be very awkward to discuss with a family during their time of acute grief as to whether they've considered the possibility of their relative's organs being donated to others. But there would be nothing worse than taking away the organs of someone for whom there was a chance of recovery. This is why there are stringent regulations in place for declaring someone as being brain dead. They are examined for the presence of brainstem reflexes; an intact brainstem is essential for life as it contains the brain nuclei that maintain important body functions, such as spontaneous breathing. Two senior doctors, who preferably have not been involved in the patient's care, perform this examination independently of each other, more than 24hrs apart. The primary purpose of this is to confirm beyond any doubt that it would be futile to continue mechanical ventilation; that the patient will never recover. In suitable circumstances, it would then be appropriate to maintain ventilator support to keep essential organs perfused until such time that they can be removed and used for transplantation. In cases where the organs would be unsuitable for transplantation, the patient's relatives would be informed of the doctor's findings, and their consent would be sought to turn the ventilator off.
The tests used to confirm brain death are:
- Absent corneal reflexes – touching the cornea of the eye causes you to blink; this is an unconscious response (a reflex) to prevent damage to the cornea. It is regulated by the brainstem.
- No oculocephalic reflex – also known as the doll's eye reflex. When the head is rotated from left to right, an intact brainstem causes the eyes to rotate in the opposite direction, so that the patient will continue to look up. In the case of brainstem death, the eyes will remain stationary, and so turn with the head. This is sometimes incorrectly called the vestibuloocular reflex; while it does use the same pathway as the vestibuloocular reflex, the oculocephalic reflex also utilises several pathways in the cerebrum that act to suppress it in people who are alert.
- No vestibuloocular reflex – the vestibuloocular reflex tests the function of the labyrinthine structures of the ear, which, together with vision, are used by the brain to gauge movement of the body relative to its surroundings. This is examined using the caloric test. Ice-cold water is placed into the left ear canal; a patent vestibulooccular reflex will cause the patients eyes to start flicking toward the right (nystagmus). If the eyes remain still, the reflex is absent. This is then repeated with the right ear a few minutes later.
- Fixed pupils – there are several pupillary reflexes that are mediated by the brainstem. In the case of brainstem death, iris tone is no longer regulated, and so the pupils become unresponsive to light (fixed). Most often they also become large (dilated), but this isn't true in all cases.
- No motor response to pain – the patient does not react to avoid a painful stimulus, such as pressure on the supraorbital ridge (the edge of bone just above the eye socket) or on compression of the finger's nail beds. Spinal reflexes (such as tendon reflexes) will still be patent, and so should be ignored as they don't involve the brainstem.
- No cough or gag reflex – no reaction to pharyngeal, laryngeal or tracheal stimulation.
- Absence of spontaneous breathing – determined by turning off the respirator and allowing the level of CO2 in the blood to rise to the level of 6.7kPa; the level by which spontaneous respiration should have been triggered. Oxygenation is maintained while this occurs by placing a catheter delivering 100% O2 in the endotracheal tube.
Reference
- Kumar P, Clark M, 2005, "Clinical Medicine", 6th edition, Elsevier Saunders, 990