The Differences Between Brain Death, Coma, and Vegetative State

You may have noticed over the past week several major news stories of brain dead or comatose people, their loved ones, and their unfortunate circumstances.  For many years neurologists have been concerned about the substantial confusion that exists regarding what is meant by certain terms that are utilized by the media pertaining to types of impaired consciousness.  Brain death, coma, and vegetative state are in fact very specific terms in clinical medicine, and there are volumes of medical literature describing and discussing all of them.  So today I will take off my sleep medicine hat, put on my neurology hat, and do my best to define these terms and distinguish them from each other for you, as briefly and succinctly as possible.


These 3 terms all refer to altered states of consciousness.  They are distinctly different from conventional sleep, which is a normalpredictable, temporary, diurnal and readily reversible state of unconsciousness necessary in and common to virtually all animal species.  All 3 of these states are generally bad–that is, with very few exceptions (such as drug-induced coma to prevent prolonged and life-threatening seizures, for example)–but neurologically speaking they are associated with varying levels of badness, not only in terms of unawareness of the patient’s environment but also in terms of prognosis for eventual “meaningful” neurologic recovery (i.e., return of consciousness with abilities to function independently, engage in basic activities of daily living, and enjoy the process of life).

Coma refers to deep sustained unconsciousness.  The patient is alive, but there is no sign of conscious or behavioral movement, vocalization, or voluntary eye opening.  The patient cannot be awakened; he or she does not respond to verbal commands or other conventional stimuli.  However, physical examination may demonstrate basic neurologic reflexes and variable (usually primitive or abnormal) responses to painful (“noxious”) stimuli.  There are a great many potential causes, including stroke, brain hemorrhage, severe closed head injury, medications, hypothermia, drug overdose, and prolonged deprivation of oxygen (such as from drowning or cardiac arrest).  The chances of someone regaining consciousness and substantial neurologic function depend on a variety of factors, including the nature, duration and severity (and potential reversibility) of the underlying cause(s), the duration of the coma, and how severe the coma is based on a thorough physical neurologic examination conducted by physicians.  In general, however, if the cause is severe and irreversible, and if the patient remains comatose for a long time (such as several weeks) following an injury, the likelihood of meaningful neurologic recovery is unfortunately small, even if he or she remains technically alive.

Vegetative state is a term is so deeply entrenched in the medical and popular literature that it is still utilized clinically.  In this form of impaired consciousness, the patient episodically appears awake but does not demonstrate evidence of awareness of self or environment; some refer to this as a state of “wakeful unconsciousness.”  The patient may appear awake upon casual observation, open and move the eyes, and exhibit sleep-wake cycles.  However, voluntary movements or vocalizations and purposeful behavioral responses to conventional stimuli are not observed.  It is usually associated with severe injury to the brain and it is prolonged in duration.  Basic brainstem functions are preserved, allowing the patient the possibility of many years of life in this fashion.  Unfortunately, this neurologic condition can be confusing (and often agonizingly so) for family members and clinicians, because signs on neurologic examination, the “depth” of neurologic impairment, causes and outcomes can all be so highly variable, and because the patient appears awake, though signs of awareness remain absent.

Brain death is the ultimate badness, referring to the complete and irreversible absence of all neurologic activity in the brain.    Physical examination demonstrates an absolute lack of response to stimuli; there are no movements or reflexes.  Diagnostic tests, such as electroencephalography (EEG), demonstrate an absence of brain and brainstem electrical activity.  The patient does not breathe without the assistance of a mechanical ventilator; when the ventilator is stopped, there is sustained apnea.  If other potentially reversible “mimics” of brain death (such as barbiturate intoxication and hypothermia) are ruled out, and if brain death is certain, there is no coming back from this; there is no chance of return of neurologic function or meaningful neurologic recovery.  Though historically people have thought of death as the permanent cessation of heart function and breathing, many people and most clinicians consider brain death consistent with clinical death, even if mechanical ventilation can keep vital organs of a brain-dead person functioning for long periods of time.  The Uniform Determination of Death Act (UDDA) is a draft state law approved for the United States in 1981 and has been adopted by most states.  It defines death as “either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem,” the determination of which is made “in accordance with accepted medical standards.”

There are several important issues to bring up briefly here.  First, it’s important to recognize that these terms may be confused with each other in the media, and sometimes even used interchangeably; be very careful of what you read and hear, and be prepared to challenge terms that are used.  Second, the clinical condition and neurologic status of the comatose or vegetative patient can change and evolve over time, and sometimes highly improbable or unexpected outcomes have been reported to occur without explanation or warning, such as spontaneous neurologic improvement following sustained coma for example; as one of my mentors once told me during my residency, “patients don’t read the textbooks.”  Finally, and importantly, there is an ongoing debate regarding the ethics of what these decreased levels of consciousness may mean for the patient, how loved ones should make decisions on behalf of the patient, and how society defines or views the concepts of death and a meaningful life over time.  These are all obviously very complex issues, affected and influenced by individual, ethnic, generational, and religious differences.  But we all–particularly those in the media–should at least strive to keep our terms and definitions as accurate and appropriately descriptive as possible, for the sake of ourselves and our loved ones.


7 comments on “The Differences Between Brain Death, Coma, and Vegetative State

  1. flbells says:

    Under the UDDA brain death is death. How does that relate to life sustaining treatment? Is there any life sustaining treatment for somebody who is brain dead?

    • Thank you for writing in. I suppose the answer depends on how one defines “life-sustaining.” If this term is defined as simply keeping cardiac function and oxygenation to organs going, then mechanical ventilation and other medical measures may be utilized in someone who is so neurologically impaired that he/she will surely experience permanent cessation of heart and lung function without them. But for most people and for most physicians, brain death is considered a form of death, even if “life-sustaining” measures are in place to keep the heart beating, as the consciousness and “essence” of the person are permanently gone because all brain and brainstem function has ceased.

  2. Thank you, Adeyemi0670! Much appreciated!

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