A long-term state of unconsciousness caused by damage to the brain
If large areas of both sides of the brain or the brainstem are damaged, coma may result. In persistent vegetative state, the parts of the brain that control higher mental functions, such as thought, are damaged. However, the areas that control vital automatic functions, such as heart rate and breathing, are intact. Although the affected person is physically and mentally unresponsive to noise, light, and other stimuli, he or she can breathe without any assistance. Random movements of the head or limbs may occur.
People in a persistent vegetative state appear to have normal sleep patterns, with their eyes closing and opening as if sleeping and waking. However, they do not appear to feel physical sensations, such as pain, or experience emotional distress. Since areas of the brain that control breathing and other vital functions are intact, a person in a persistent vegetative state can remain alive for months or even years, provided appropriate medical treatment is given.
The most common cause of the condition is a severe head injury. It can also be caused by an infection of the brain, such as viral encephalitis, or by oxygen deprivation of the brain as a result of near-drowning or cardiac arrest.
The diagnosis of persistent vegetative state is made if a person who is unconscious fails to respond to stimulation or to communicate, but vital functions, such as breathing, are maintained. There is no evidence that the mind of the person is functioning consciously.
There is no treatment for persistent vegetative state. However, general supportive measures and nursing care will ensure that an affected person is kept as comfortable as possible. A person in a persistent vegetative state can live for several years, but recovery is unlikely.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.