Persistent vegetative state
Persistent vegetative state (PVS) is a chronic disorder of consciousness. Disorders of consciousness are caused by injuries or illnesses affecting the central nervous system. PVS is chronic, and most people do not recover.
Definition & Facts
PVS differs from comatose states (another disorder of consciousness) as the patient is aroused, or partially awake, but lacks awareness of self and environment. In a coma, the person is both asleep and unaware. Coma may progress to PVS, or the person may recover both arousal and awareness.
The “persistent” in PVS refers to the chronic nature of the loss of consciousness, and “vegetative” refers to the fact that neurovegetative (autonomic) functions, like breathing and digestion, are intact. However, the person is considered to lack all awareness.
Individuals may recover from PVS, and progress to stages of partial or full awareness. Those people who recover from PVS may have lingering mental and physical deficits; the longer a person has been unconscious, the likelier they are to have cognitive deficits.
Symptoms & Complaints
As coma progresses, neurovegetative functions can recover upon which the individual is considered to be in a vegetative state (VS). A person in a VS has a sleep-wake cycle. They may track objects with their eyes, but not when asked to do so. They may show signs of pain or facial expressions. However, these reactions are not purposeful.
PVS is usually preceded by brain injury, which may be traumatic (such as a car accident, assault or fall) or acquired (such as a stroke or infection). Sometimes PVS is caused by genetic disorders that affect the central nervous system. The exact cause of PVS relates to the effect that the injury, illness, or genetic disorder has on parts of the central nervous system, specifically the brain, that regulate consciousness.
The brain areas involved in consciousness are widespread, but ones which are particularly important include the brainstem (an area at the base of the brain which is involved in neurovegetative functions, and regulation of arousal or transition from wakefulness to sleep), the thalamus (an area at the center of the brain which connects sensory and motor functions throughout the brain), and the cerebral cortex (the surface of the brain where sensory information and motor plans come together to guide action).
In the cerebral cortex, the frontal lobe and parietal lobe are particularly important in regulating consciousness. These areas may be directly damaged by trauma sustained in the initial injury or illness or by swelling occurring secondary to that initial cause.
Diagnosis & Tests
A person in a vegetative state will likely already be hospitalized and under the care of a neurologist. Neurologists generally treat disorders of consciousness. Some neurologists, especially those who work in a neurointensive care unit at a hospital, or at a specialized rehabilitation hospital, specialize in disorders of consciousness.
A diagnosis of PVS can lead the physician to recommend that a person be allowed to pass away because of their poor prognosis. Because of this, it is vital that the diagnosing physician makes sure the person is truly in a PVS and not minimally conscious. Currently, the best way to make this diagnosis is by testing the person’s ability to move their eyes, move their muscles, and speak in response to external stimuli.
Magnetic resonance imaging (MRI) scans and electroencephalograms may be taken during the diagnostic process. These tests involve recording the brain's response to verbal instructions. A minimally conscious state (MCS) will need to be ruled out. This is challenging because up to 24 percent of people who are diagnosed in a persistent vegetative state may actually be in a minimally conscious state.
Patients in a minimally conscious state may be able to follow simple instructions, such as eye blinks for ‘yes’ and ‘no’, may be able to speak in an understandable (but limited) way, and may show purposeful eye movement. Those in a minimally conscious state may respond to treatment or may have a chronic condition.
Treatment & Therapy
Currently, there is no reliable treatment for PVS. While people in vegetative or minimally conscious states may respond to treatments, PVS is chronic. Either the person recovers independently, or they show no further recovery and are allowed to pass away.
Those who are in a PVS will be provided adequate supportive care. Providing for the patient's hygiene, moving them regularly to prevent bed sores, using and managing catheters to facilitate hygienic urination and defecation are all aspects of caring for a patient with PVS.
Sensory stimulation is a possible form of treatment for comas that involves using stimuli like familiar music, beloved objects, and visual stimulation that may arouse the person’s memories and cause them to progress to greater states of emotional awareness. The use of sensory stimulation in people with PVS is very controversial, as most people in PVS who respond to these therapies, are considered to be in an undiagnosed minimally conscious state.
Prevention & Prophylaxis
Acquired brain injury such as stroke can be avoided by keeping a healthy cardiovascular system, i.e., quitting smoking or never beginning to smoke in the first place, avoiding secondhand smoke, drinking alcohol in moderation or avoiding alcohol, and staving off obesity with regular exercise and healthy diet. Genetic disorders are typically prevented only through early diagnosis and treatment.