How Brain Death Is Diagnosed

Conditions that must be met before a diagnosis can be made

Blurred motion view of patient lying in bed in intensive care unit
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There is more to the loss of consciousness than not being awake. Sleep and coma, for example, each involves the loss of consciousness and are largely defined by the time it takes to return to consciousness. Even a person in a persistent vegetative state (PVS) has the possibility, albeit slight, of waking up.

Brain death is different. As the term suggests, brain death indicates that there is no brain activity and, as such, no hope of recovery.

Medically speaking, brain death is the definitive diagnosis of death.

Understanding Brain Death

Unlike the other forms of lost consciousness, brain death involves a complete loss of brainstem function. What this means is that the reticular activating system—the diffuse network of nerve connecting the spinal cord and brain—has been irreversibly damaged. It also indicates that the parts of the brain regulating respiration and heart activity have been irrevocably destroyed.

Brain death can be a concept that some people find hard to grasp. Because we instinctively associate death with a heart that has stopped beating, we often overlook the fact that is the brain that delivers the impulses that "run" the heart.

While life support equipment can be used to maintain respiration and circulation, there is no such device that can keep a brain running. Ultimately, if the brain dies, the rest of the body will certainly follow.

Diagnosing Brain Death

There are a number of conditions that must be met for brain death to be declared. While state or local laws may require additional actions, the construct of the diagnosis is universally accepted as being definitive. In short, to declare someone brain-dead:

  1. The coma must be irreversible with either a known or proximate cause.
  1. The person must have no brainstem reflexes.
  2. The person has no respiratory function.

All three conditions must be satisfied for brain death to be declared.

Establishing the Irreversibility and Cause of the Coma

Before a doctor can determine whether the coma is irreversible, he or she must find if there is any way to reverse it. To do so, the medical team must first pinpoint the cause (or most likely cause) of the coma.

Moreover, the team must exclude any condition that could potentially mimic brain death, such as hypothermia, drug toxification or poisoning, metabolic abnormalities, or neuromuscular agents that can cause "death-like" paralysis. All of these, by varying degrees, are potentially reversible.

Establishing the irreversibility of a coma requires that the doctor wait an appropriate amount of time-based on the known or proximate cause. The determination that must meet both medical and legal standards. From this perspective, the term "proximate" indicates that the cause must be sufficiently established and supported if it is not already known.

Establishing the Absence of Brainstem Reflexes

Brainstem reflexes are automatic responses that are no different to the knee-jerk tests given at the doctor's office.

They are reflexive actions that indicate whether a person's neurological functions are normal, abnormal, or absent.

A person is considered brain-dead if he or she fails to respond to all of the following reflex stimuli :

  • Lack of pupillary reflex means that the person's pupils do not respond in any way when a light is shined on them. If the person were alive, the pupils would get smaller.
  • Lack of corneal reflex means that the person does not blink and have any response when the doctor touches the eye with a cotton swab or drop of water.
  • Lack of oculocephalic reflex (also known as the "doll's eye" reflex) means the person's eyes will not fixate on the examiner's face when his or her head is moved from side to side.
  • Lack of the gag reflex means that the person will not gag, cough, or react when the back of the throat is touched with a cotton swab or a suction device.
  • Lack of response to cold caloric testing means that the person will not respond when ice water is squirted into the ear. If the person were alive, the stimuli would cause the person's eyes to move in the opposite direction as it effectively "tricks" the inner ear into thinking that the person is spinning.

Establishing the Absence of Respiratory Function

The final step in establishing brain death is the apnea test. Apnea is the medical term for the suspension of breathing and is used in this instance to ascertain whether the suspension is permanent.

To perform an apnea test, the doctor would take the following steps:

  1. The person on a mechanical ventilator would be connected to a pulse oximeter. This is the device used to measure the saturation of oxygen in the blood.
  2. The ventilator would then be disconnected and a tube would be inserted into the person's trachea to deliver 100 percent oxygen to the lungs. This ensures the person is never oxygen-deprived if he or she does respond.
  3. Blood tests would immediately be performed to measure baseline blood gases.
  4. The doctor would then wait for eight to 10 minutes to see if there is any response from the patient.
  5. After eight to 10 minutes, the blood gases would again be tested.

If there is no respiratory movement and the PaCO2 (pressure of carbon dioxide in the arteries) has increased to over 60—meaning that there has been no exchange of oxygen and carbon dioxide in the lungs—the person will be declared brain-dead.

If on the other hand, a respiratory movement is observed, then the person cannot be considered brain-dead. Further investigations would then be performed to identify what, if anything, can be done to reverse the condition.​

Additional Tests

If a full clinical examination is performed (including brainstem reflexes and apnea tests) and brain death is declared, no additional testing is required. With that being said, because of the grave nature of the diagnosis, most hospitals today require that a confirmatory examination is performed by a different qualified physician after an allotted period of time.

In some cases, additional tests may be performed if facial injury, spinal cord injury, or other factors make it impossible to complete a standard assessment. These additional tests can provide family members with further assurance that the correct diagnosis was made.

Source:

Wijdiks, V.; Varela, P.; Gronseth, G. et al. "Evidence-based guideline update: Determining brain death in adults - Report of the Quality Standards Subcommittee of the American Academy of Neurology." Neurology. 2010; 74(23). DOI: 10.1212/WNL.0b013e3181e242a8.