After a severe injury or illness that affects the brain, patients can fall into a persistently unconscious state, rendering them unaware of themselves or their environment. Depending on their level of consciousness, patients are considered to be comatose, in a minimally conscious state, in a persistent vegetative state, or brain dead. In the first three situations, these states can dictate treatment as well as how to prepare family members for decisions regarding the patient's prognosis and quality of life.
In this state, either the thalamus, the brainstem, or both hemispheres of the brain are damaged. Patients cannot be awakened, are unresponsive to stimuli such as pain, sound, or touch, and do not experience sleep-wake cycles.
If the lower part of the brainstem has also been damaged, the patient often requires a ventilator to breathe. Coma is caused by a severe brain injury such as a traumatic head injury, brainstem stroke , or a brain hemorrhage that affects the surrounding tissue and brain structure, as well as severe hypothermia, drug overdose, drowning, and cardiac arrest.
Regaining consciousness depends on the cause and severity of the injury and how long the coma lasts. Most patients eventually awaken to some degree. A number of tests are carried out to check for brain death, such as shining a torch into both eyes to see if they react to the light. After brain death, it may be possible for the person's organs to be used in transplants, which can often save the lives of others.
In cases where a deceased person has not made their wishes clear, deciding whether to donate their organs can be a difficult decision for partners and relatives.
Hospital staff are aware of these difficulties and will try to ensure the issue is handled sensitively and thoughtfully. Page last reviewed: 01 April Next review due: 01 April Overview - Brain death Contents Overview Diagnosis. Brain death is legal death If someone's brain dead, the damage is irreversible and, according to UK law, the person has died. The brain stem The brain stem is the lower part of the brain that's connected to the spinal cord part of the central nervous system in the spinal column.
These include: breathing heartbeat blood pressure swallowing The brain stem also relays information to and from the brain to the rest of the body, so it plays an important role in the brain's core functions, such as consciousness, awareness and movement.
After brain death, it's not possible for someone to remain conscious. A head injury Overview of Head Injuries Head injuries that involve the brain are particularly concerning. A disorder that deprives the brain of oxygen, such as cardiac arrest Cardiac Arrest and CPR Cardiac arrest is when the heart stops pumping blood and oxygen to the brain and other organs and tissues. Sometimes a person can be revived after cardiac arrest, particularly if treatment is However, any disorder that severely damages the brain such as bleeding hemorrhage Intracerebral Hemorrhage An intracerebral hemorrhage is bleeding within the brain.
Intracerebral hemorrhage usually results from chronic high blood pressure. The first symptom is often a severe headache. Diagnosis is Another group of brain disorders, called spongiform encephalopathies, are caused by People in a vegetative state can do some things because some parts of the brain are functioning:. They have relatively regular sleeping and waking patterns but not necessarily related to day and night. Because of these responses, they may appear to be aware of their surroundings.
However, they have no awareness of themselves or their environment. Their apparent responses to their surroundings result from automatic 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 Functional MRI In magnetic resonance imaging MRI , a strong magnetic field and very high frequency radio waves are used to produce highly detailed images.
MRI does not use x-rays and is usually very safe Electroencephalography EEG is a simple, painless procedure in which In these people, the cause was usually a head injury, not a disorder that resulted in the brain being deprived of oxygen. 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.
Awareness that can be detected only by these tests is called covert hidden consciousness. People in a vegetative state have no control over urination and bowel movements are incontinent. People in a vegetative state go to sleep and awaken regularly, and their eyes open and move, but typically, they have lost all capacity for thought and conscious behavior.
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 Minimally Conscious State A minimally conscious state is severe but not complete impairment of awareness.
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 Positron Emission Tomography PET Positron emission tomography PET is a type of radionuclide scanning.
A radionuclide is a radioactive form of an element, which means it is an unstable atom that becomes more stable by releasing These tests can indicate how well the brain is functioning.
Electroencephalography Electroencephalography Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. This test can detect when a person responds to questions and commands, even when the response is not apparent—that is, when the person does not speak or move in response covert consciousness.
EEG can also detect this brain activity. The results of these tests can affect decisions about long-term care. Some people spontaneously recover from a vegetative state, but recovery is usually incomplete. 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 major stroke or cardiac arrest.
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