March 24, 2007 05:44 PM
National Catholic Bioethics Center
Current Issue of Ethics and Medic March 2007
Part one of a two part series.
Understanding Brain Death Diagnosis
UNDERSTANDING BRAIN DEATH DIAGNOSIS
First of a Two-part Series
John M. Travaline, M.D., F.A.C.P.
In this issue, Dr. Travaline presents the medical criteria for the determination of death by neurological criteria. In the May issue, he will examine the theological and moral implications of this diagnosis.—Ed.
The medical concept of brain death continues to stimulate interest and debate in the fields of bioethics, philosophy, religion, law, and medicine. Even outside these spheres of interest, tragedies that involve this diagnosis routinely affect the lives of many people. Despite well-established criteria and procedures for the determination of brain death, the concept remains poorly understood, and the confusion surrounding it is particularly troublesome for a layperson who has a severely injured or ill family member. I endeavor here to clarify common misconceptions about this condition, and to explain the process of making this diagnosis.
The expression “determination of death by neurological criteria” is technically more accurate for this process, but I will use the more common phrase “brain death diagnosis” in this essay.
Background and Definition
The concept of brain death first received attention in 1968,1 and represented a response to rapidly evolving medical technology which made it possible to sustain a patient’s basic cardiopulmonary function in the presence of obvious and severe brain injury. When such technology is used, death cannot be determined with certainty by conventional criteria (cessation of breathing and heartbeat).
In addition to emerging as a response to new medical technologies, the diagnosis of brain death allows organs to be harvested for transplantation into desperately ill patients. In the United States, over twenty-two thousand organ transplants occurred from January to September 2006, with approximately six thousand deceased donors providing the organs.2 Brain death is an important precondition for organ procurement agencies to ensure appropriate sources of transplantable organs such as kidney, heart, liver, and lung.
In essence, the criteria for brain death represent an alternative means of determining death. For legal purposes, the criteria are expressed in the Uniform Determination of Death Act:
An individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead. A determination of death must be made in accordance with accepted medical standards.3
Brain death constitutes the death of an individual, and is recognized as death just as irreversible cessation of heartbeat and breathing is. There is one form of death, but two acceptable means of determining it.
Nature of the Diagnosis
Brain death occurs when the brain completely stops functioning. Conditions in which a physician may suspect brain death include severe head trauma and extensive bleeding into the brain from a stroke or ruptured aneurysm. In such cases, the patient’s heart, because it is not dependent on any other organ to function, continues to beat, usually in a normal way. In addition, the patient will be connected to a mechanical ventilator (sometimes called a respirator) that rhythmically allows oxygen-enriched air to flow in and out of the lungs. A patient who is brain dead thus typically has a beating heart and, while connected to a ventilator, appears to be breathing. Therefore, cardiopulmonary criteria for death are not met, and the physician may consider the diagnosis of brain death.
Key Elements in the Diagnosis
There are two key criteria for the determination of brain death. First, there must be cessation of all functions of the entire brain, including the brain stem. Determining cessation is commonly achieved by means of physical examination. Neurologists or neurosurgeons, experts in assessing brain function, perform this examination. The examination mainly comprises assessments of brain stem reflexes and of spontaneous breathing effort, the latter determined by an apnea test. These functions constitute the most basic brain activity and therefore, if absent, denote cessation of brain function.
The second key criterion for the determination of brain death is that the cessation of brain function be irreversible. To ensure confidence in the neurological examination, and to help establish irreversibility, a second examination is performed several hours after the first. If an adequate assessment cannot be made by physical examination, a physician will perform a confirmatory test. Confirmatory tests include electroencephalography (EEG), and cerebral perfusion studies. EEGs reveal whether brain activity is present, and perfusion studies reveal whether the brain is receiving any blood flow.
A few important conditions may mimic brain death but are potentially reversible, and they must, therefore, be excluded as diagnostic possibilities. These conditions include specific drug intoxications, severe metabolic disorders, and hypothermia (severe reduction in body temperature). Physicians will use various clinical tools to evaluate a patient for the presence of these conditions. If such conditions are absent, and the patient meets the criteria for cessation of all brain function, the diagnosis of brain death is established.
A Closer Look at the Apnea Test
The apnea test is one of the procedures for determining brain death mentioned above. “Apnea” refers to the absence of breathing. Since the control center for breathing is located in the brain stem, this test specifically assesses a brain stem function; in the context of a brain death evaluation, the presence of apnea means that the brain stem has ceased to function.
Patients who are being evaluated for the possibility of brain death receive mechanical ventilation, which means they are connected to a machine that is “breathing for them.” To assess for apnea, the mechanical ventilator must be removed. The purpose of the apnea test is to remove the ventilator and observe the patient for the presence of any breathing efforts. If breathing efforts occur, the physician knows that the brain stem is functioning, at least to some degree, and the patient is not brain dead. A confusing aspect of the apnea test is that some people think the removal of the ventilator can precipitate or cause a patient’s death by depriving the patient of oxygen, which is known to be essential for brain function. This is not the case, however. To clarify this point, a basic understanding of a ventilator’s function, and how a patient is connected to it, is in order.
A mechanical ventilator has two major functions. One is to deliver oxygen into a patient’s lungs, and the second is to provide a means of ventilation. Ventilation basically involves the removal of carbon dioxide, an unwanted byproduct of metabolism, which is normally eliminated from the body when a person exhales.
A patient receiving mechanical ventilation has a flexible plastic tube inserted through the mouth and into the trachea (windpipe). The external end of this “breathing tube” is connected to tubing from the ventilator, forming a conduit from the patient’s lungs to the ventilator through which air flows so that oxygenation and ventilation can occur. During an apnea test, the patient is temporarily disconnected from the ventilator, but the administration of oxygen, essential for brain function, continues. Prior to the removal of the ventilator, the patient is first given pure oxygen through the ventilator. Although this maximally saturates the patient’s blood with oxygen, over time the level of oxygen in the blood will decrease. If it gets too low, the patient may be harmed. To avoid this, a continuous source of oxygen is provided even after the ventilator is removed. This is achieved by connecting the patient’s breathing tube to an alternative source of pure oxygen, thus ensuring that the patient receives the maximal amount of oxygen possible.
With the patient removed from the ventilator and receiving oxygen, the apnea test continues for up to ten minutes. This is done to allow carbon dioxide to accumulate in the patient’s blood. Carbon dioxide is an extremely potent stimulus for the brain stem to initiate breathing: if the brain stem is functioning and the blood level of carbon dioxide is elevated, a patient’s breathing effort will increase.
Since the ventilator is disconnected during the apnea test, no ventilation occurs, and carbon dioxide accumulates in the patient’s blood. The threshold level of carbon dioxide (the level that stimulates breathing) is known, and a physician can ensure that it has been reached by performing a simple and routine blood test. If the stimulus is adequate and no breathing effort occurs, this function of the brain stem has ceased. Brain death is then confirmed.
The brain death concept has been a part of clinical medicine for nearly four decades and is likely to remain an important diagnosis. Since the situations which involve this diagnosis are often emotionally charged, and concern a patient’s death, a clear understanding of some of the clinical aspects of this diagnosis should help relieve misgivings about it.
John M. Travaline, M.D., F.A.C.P.
Associate Professor of Medicine
Temple University School of Medicine
Philadelphia, Pennsylvania
1 “A Definition of Irreversible Coma: Report of the Ad Hoc Committee of the Harvard Medical School to Examine the Definition of Brain Death,” Journal of the American Medical Association 205.6 (August 5, 1968): 337–340.
2 Organ Procurement and Transplantation Network, “Transplants Performed January–September 2006” and “Donors Recovered January–September 2006,” http://www.optn.org/data. Based on OPTN data as of January 12, 2007.
3 National Conference for Commissioners on Uniform State Laws, “Uniform Determination of Death Act,” approved by the American Medical Association October 19, 1980, http://www.law.upenn.edu/bll/ulc/fnact99/1980s/udda80.htm
