brain stem function but no brain activity

Because of this property, they are accumulated proportional to the blood flow in normal gray matter including brain cells of cerebrum, cerebellum, and brainstem. Both of them are brain specific, lipophilic and after intravenous injection, they cross the blood brain barrier. There are two other radiopharmaceuticals, namely Tc99m-HMPAO (hexamethylpropyleneamine oxime) and Tc99m-ECD (ethyl cysteinate dimer). However, Tc99m-DTPA tracer has low resolution for brain vascular flow. DTPA does not have the ability to cross the intact blood brain barrier, so intracranial blood flow is seen in normal patients. One of the radioactive tracers used is Tc99m-DTPA. After bolus intravenous injection of the tracer, brain vascular flow is estimated. In this technique, a gamma emitting radioactive tracer is intravenously injected and is detected by a radio counter in the nuclear medicine. This is another gold standard ancillary imaging test for determination of brain death. Thus, it is an expensive procedure and not readily available in many hospitals and may not be easy to interpret in many healthcare facilities. It can have “stasis filling” due to diffusion of contrast in the static column of blood, which can result in false negatives. Other disadvantages include transportation of patents to the angio suite requires expert operator to perform is invasive and requires injection of contrast medium that may have a potential risk to the patients with kidney diseases. But this method does not have the spatial resolution to distinguish the blood flow in the different parts of the brain such as brainstem. The criteria for brain death diagnosis using this method include no intracerebral filling at the level of entry into the skull of carotid or vertebral artery and filling of external carotid arteries.

This test is capable of detecting dynamic blood flow in the arteries, veins, and capillaries.

These show continued filling of the extracranial arteries including (A) left and (B) right external carotid arteries. Here, we provide description of cerebral blood flow imaging techniques and compare them.ĭigital subtraction angiography image of a brain dead patient showing no intracranial filling on selective (A) left and (B) right common carotid artery as well as (C) left and (D) right vertebral artery angiograms. Based on this, the first type assesses the electrical functions of the brain, and the other type analyses cerebral blood flow in the brain on imaging. The main objective of the ancillary test would be to demonstrate the absence of cerebral electric activity or cerebral circulatory arrest. If the ancillary test confirms death, when in fact, patient is not dead, is very dangerous and raises critical social, ethical and legal concerns. This is very important in brain death patients. These situations include when patients have resuscitated shock, hypothermia, severe metabolic abnormalities, complex spinal reflexes, peripheral nerve or muscular dysfunctions, high cervical spine injury, craniofacial trauma or if the patient is on sedative drugs such as alcohol, barbiturates, sedatives, and hypnotics.Īn ideal ancillary test should not have any false positive results. Ancillary imaging tests are necessary in situations when neurological examination or the apnea test cannot be performed or its validity comes into a question. Absence of brain stem reflexes includes absence of gag, cough, bilateral absence of corneal response, pupillary response to light and vestibule-ocular response, absence of respiratory efforts based on apnea test, and absence of confounding factors. The criteria for declaring brain death includes deep unresponsive coma with established etiology, absence of reversible conditions. In Canada, two physicians must determine whether particular patient is brain dead or not. It is principally established using clinical criteria including coma, absence of brain stem reflexes, and using apnea test. Brain death is defined as permanent cessation of all vital functions of the brain.

Brain stem function but no brain activity