The examination for brain death is based on response to external stimuli. Since the brain is the organ that feels outside pain, when the brain is dead the patient feels nothing. Before the examination is performed, the physician will have a toxicology test performed to make sure the patient does not have any muscle relaxants in his system, and will check that the patient's body temperature is not extremely abnormal, either of which may reduce neurological reflexes.
The positive examination for brain death includes the following:
- The patient has no response to command, verbal, visual or otherwise.
- The patient is flaccid, with areflexic extremities. The patient has no movements -- the arms and legs are raised and allowed to fall to see if there are adjacent movements, restraint or hesitation in the fall.
- The pupils are unreactive (fixed). The patient's eyes are opened and a very bright light is shined into the pupil. The light will activate the optic nerve and send a message to the brain. In the normal brain, the brain will send an impulse back to the eye to constrict the pupil. In the non-viable brain, no impulse will be generated. This is performed in both eyes.
- The patient has no oculocephalic reflex. The patient's eyes are opened and the head turned from side to side. The active brain will allow a roving motion of the eyes; the non-functional brain will not. The eyes remain fixed.
- The patient has no corneal reflexes. A cotton swab is dragged across the cornea while the eye is held open. The intact brain will want the eye to blink. The dead brain will not. This is performed in both eyes.
- The patient has no response -- either purposeful or posturing -- to supra-orbital stimulation. The patient's eyebrow ridge is compressed with the thumb. The resulting stimulation pressure will cause motion of the extremities, either purposeful or primitive posturing, in the living-brain patient, but none in the brain-dead patient.
- The patient has no oculovestibular reflex. The patient's ear canal is inspected to ensure an intact tympanic membrane and that the ear is free of wax. While holding the eyes open, ice water is injected into the ear canal. The drastic change in ear temperature will cause a violent eye twitching by the intact brain but no reaction in the brain-dead patient. This is performed in both ears.
- The patient has no gag reflex. The movement of the breathing tube (in and out) or the insertion of a smaller tube down the breathing tube will cause a gag reflex in a comatose patient, but will not elicit a reflex in the brain-dead patient.
- The patient has no spontaneous respiration. The patient is temporarily removed from life support (the ventilator). With the cessation of breathing by the machine, the body will immediately start to build up metabolic waste of carton dioxide (CO2) in the blood. When the CO2 level reaches a level of 55 mm Hg, the active brain will cause the patient to breathe spontaneously. The dead brain gives no response.
If, after this extensive clinical examination, the patient shows no sign of neurological function and the cause of the injury is known, the patient can be pronounced "brain dead." In some states, more than one physician is required to make this pronouncement in order for brain death to become legal death.
Although the patient has a dead brain and dead brain stem, there may be spinal cord reflexes that can be elicited (a knee jerk, for example). In some brain dead patients, when the hand or foot is touched in a particular manner, the touch will elicit a short reflex movement.
Many physicians will order a confirmatory test for brain death when the clinical examination demonstrates no neurological function.