A vegetative state is absence of responsiveness and awareness due to overwhelming dysfunction of the cerebral hemispheres, with sufficient sparing of the diencephalon and brain stem to preserve autonomic and motor reflexes and sleep-wake cycles.
Diagnostic Criteria for Vegetative State
The following preconditions must apply before diagnosis of the VS can be considered.
- The cause of the condition should be established as far as is possible. It may be due to acute cerebral injury, degenerative conditions, metabolic disorders, infections or developmental malformations.
- The possibility that the persisting effects of sedative, anaesthetic or neuromuscular blocking drugs are responsible in whole or part should be considered. Drugs may have been the original cause of an acute cerebral injury, usually hypoxic, but their continuing direct effects must be excluded either by the passage of time or by appropriate laboratory tests.
- The possibility that continuing metabolic disturbance is responsible for the clinical features must be considered and excluded. Metabolic disturbances may of course occur during the course of a VS.
- The possibility that there is a treatable structural cause should be excluded by brain imaging.
The following criteria are usualy met.
- The key requirement for diagnosis is that there must be no evidence of awareness of self or environment at any time; no response to visual, auditory, tactile or noxious stimuli of a kind suggesting volition or conscious purpose; no evidence of language comprehension or meaningful expression. These are al necessary conditions for the diagnosis.
- There are typically cycles of eye closure and eye opening giving the appearance of a sleep–wake cycle.
- Hypothalamic and brainstem function are usually sufficiently preserved to ensure the maintenance of respiration and circulation.
Criteria 2 and 3 are usually satisfied by patients in the vegetative state but, unlike the first criterion, they are not obligatory (thus, for example, a patient with cerebral injuries sufficient to cause the vegetative state might, incidentally, have third nerve palsies preventing eye opening, or injuries to the chest or medula affecting respiratory function).
The persistent vegetative state can be defined as a vegetative state present at 1 month after acute traumatic or nontraumatic brain injury, and present for at least 1 month in degenerative/metabolic disorders or developmental malformations.
The permanent vegetative state means an irreversible state, a definition, as with all clinical diagnoses in medicine, based on probabilities, not absolutes. A persistent vegetative state patient becomes permanently vegetative when the diagnosis of irreversibility can be established with a high degree of clinical certainty, ie, when the chance of regaining consciousness is exceedingly rare.
- Royal College of Physicians. The vegetative state: guidance on diagnosis and management. Clin Med. 2003 May-Jun;3(3):249-54. [Medline]
- The Quality Standards Subcommittee of the American Academy of Neurology. Practice parameters: assessment and management of patients in the persistent vegetative state. Neurology. 1995 May;45(5):1015-8. [Medline]
Created Oct 24, 2014.