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A vegetative state occurs when the cerebrum (the part of the brain that controls thought and behavior) no longer functions, but the hypothalamus and brain stem (the parts of the brain that control vital functions, such as sleep cycles, body temperature, breathing, blood pressure, and heart rate) continue to function. Thus, people open their eyes but otherwise do not respond to stimulation in any meaningful way. They cannot speak and have no awareness of themselves or their environment.
The vegetative state is rare. Traditionally, a vegetative state has been considered a long-lasting (chronic) disorder. That is, if a person appears to be in a vegetative state but recovers in a few weeks, that person was never in a vegetative state. When a vegetative state lasts for more than 1 month, it used to be considered a persistent vegetative state, but now, doctors seldom use that term. A very few people who have been in a vegetative state for more than 1 month continue to improve over months to years, particularly if the cause was brain damage due to a head injury (traumatic brain injury—see Overview of Head Injuries).
How many people are in a vegetative state is unknown, but about 25,000 people in the United States are thought to have this disorder.
Most commonly, a vegetative state is caused by severe brain damage due to
However, any disorder that severely damages the brain such as bleeding (hemorrhage) or an infection in the brain can result in a vegetative state.
People in a vegetative state can do some things because some parts of the brain are functioning. They can open their eyes. They have relatively regular sleeping and waking patterns (but not necessarily related to day and night). They can breathe, suck, chew, cough, gag, swallow, and make guttural sounds. They may even be startled by loud noises and appear to smile or frown. Because of these responses, they may appear to be aware of their surroundings. However, these apparent responses to their surroundings result from involuntary basic reflexes and not from a conscious action. For example, they may instinctively grasp an object when it touches their hand, as a baby does.
People in a vegetative state cannot do things that require thought or conscious intention. They cannot speak, follow commands, move their limbs purposefully, or move to avoid a painful stimulus.
Most people in a vegetative state have lost all capacity for awareness, thought, and conscious behavior. However in a few people, functional magnetic resonance imaging (fMRI—see Functional MRI) and electroencephalography (EEG—see Tests for Brain, Spinal Cord, and Nerve Disorders : Electroencephalography) have detected evidence of some awareness. When the people were asked to imagine moving a part of their body, these tests showed appropriate brain activity for such an action (although the people did not do the action). However, these tests cannot determine how much awareness these people have.
People in a vegetative state have no control over urination and bowel movements (are incontinent).
Doctors suspect a vegetative state based on symptoms. However, before a vegetative state can be diagnosed, people should be observed for a period of time and on more than one occasion. If people are not observed long enough, evidence of awareness may be missed. People who have some awareness may be in a minimally conscious state (see Minimally Conscious State) rather than a vegetative state.
An imaging test, such as magnetic resonance imaging (MRI) or computed tomography (CT), is done to check for disorders that may be causing the problem, especially those that can be treated. If the diagnosis is in doubt, doctors may do other imaging tests—positron emission tomography (PET) or single-photon emission computed tomography (SPECT—see Radionuclide Scanning).
Electroencephalography (EEG) may be done to check for abnormalities in the brain's electrical activity that suggest seizures, which may impair consciousness.
Some people spontaneously recover from a vegetative state. The chances of recovery depend on the cause and extent of the brain damage and the person's age, as for the following:
Some recovery is more likely if the cause is a head injury, a reversible metabolic abnormality (such as low blood sugar), or a drug overdose rather than a stroke or cardiac arrest.
Younger people may recover more use of their muscles than older people, but differences in recovery of mental function, behavior, and speech are not significant.
If a vegetative state lasts for more than a few months, people are unlikely to recover consciousness. If people do recover, they are likely to be severely disabled.
The longer a vegetative state lasts, the more severe the disabilities are likely to be.
Recovery from a vegetative state is unlikely after 1 month if the cause was anything other than a head injury. If the cause was a head injury, recovery is unlikely after 12 months. However, a few people improve over a period of months or years. Rarely, improvement occurs late. After 5 years, about 3% of people recover the ability to communicate and understand, but few can live independently, and none can function normally.
Most people who are in a vegetative state die within 6 months. Most of the others live about 2 to 5 years. The cause of death is often a respiratory or urinary infection or severe malfunction (failure) of several organs. But death may occur suddenly, and the cause may be unknown.
People in a vegetative state require the same long-term care as people in a coma (see Long-term care), particularly measures to prevent problems that immobilization can cause, such as pressure sores and permanent stiffening of muscles (contractures—see Coma and Impaired Consciousness:Long-term care).
If recovery is unlikely, doctors, family members, and sometimes the hospital ethics committee should discuss how aggressively future medical problems should be pursued and when and if life-sustaining treatment should be withdrawn. A person's wishes about such treatments should be considered if they are known—for example, if wishes have been stated in an advance directive (living will—see Advance Directives : Living Will).
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