How to Diagnose Brain Death

When patients in the ICU suffer devastating neurologic injury, it can be difficult to tell that they are truly brain dead. These patients are often on medications that keep them heavily sedated or even paralyzed, are on mechanical ventilators that control their breathing, and may be on pressor medications such as norepinephrine, phenylephrine and vasopressin to support their blood pressure.

Thus, when an ICU patient becomes brain dead the event may not be preceded by any drastic changes in their status. However, brain death may be suspected in ICU patients when there is a change in their neurological exam.

Individuals who are dead will lose their basic brainstem reflexes. Their pupils will become fixed and dilated, they will have no gag reflex or any of the other brainstem reflexes that are checked several times a day.

However, the loss of an individual's basic brainstem reflexes are not always enough to declare a patient brain dead. Criteria have been developed in order to assist physicians in officially determining a person is truly brain dead. The Harvard criteria and Minnesota criteria are often used to diagnose brain death.

The Harvard and Minnesota criteria utilize the seven steps discussed below that are required to diagnose brain death.

1. The patient has no spontaneous movements.

2. The patient does not respond to any painful stimuli such as the sternal rub or nail pinch.

3. The brainstem reflexes are entirely absent. The brainstem reflexes include:

-fixed and dilated pupils in a patient who is not on adenosine and has not received atropine.

-absent response to caloric stimulation in the ear

-absent corneal reflex

-absent gag reflex

-absent "doll's eye" phenomenon

4. Apnea test indicates no spontaneous respiration. The apnea test is performed as follows:

An arterial line and pulse oximeter are in place. The FIO2 is adjusted to 1.0 (100% oxygen) and if necessary it is ensured that the PaCO2 is 40 to 50mmHg. The first arterial blood gas (ABG) is drawn. Then the ventilator is disconnected and oxygen is insufflated at 6 L/min to prevent hypoxia. After 10 minutes draw the second ABG and the patient is reconnected to the ventilator. in brain death, the rise in PCO2 during the apneic period should exceed 10mmHg with no respiratory effort seen.

5. Possible exacerbating conditions must be ruled out. These conditions include:

-Central nervous system depressants

-Hypothermia (core temperature <32.2 celsius)

-Electrolyte disturbances (hyponatremia, metabolic acidosis)

-Neuromuscular blocking agents (check this with a nerve stimulator & reverse with neostigmine if needed)

6. Establish that the condition causing supposed brain death is due to irremedial structural brain damage.

7. Verify clinical findings unchanged with a reappraisal 12 to 24 hours after the initial brainstem reflex and apnea test.

Brain death can be difficult to detect in patients in the ICU. Electroencephalograms and radionuclide cerebral blood flow scans are not required to diagnose brain death, but are considered confirmatory if they are done. However, all that is truly required to diagnose brain death in a patient are the seven Harvard and Minnesota criteria.

Reference:

Harvard Criteria for Brain Death.

Minnesota Criteria for Brain Death.

UpToDate Online.