The most important thing to know about PVS is that it probably doesn't exist.   "By definition, patients in a persistent vegetative state are unaware of themselves or their environment.  They are noncognitive, nonsentient, and incapable of conscious experience. "  Nonsense.

This belief closes off any road into the condition through communication.  This is a serious matter. 

If people do not communicate awareness, why do we not begin from the standpoint that this a deficit in communication, rather than leaping to a conclusion that there is a deficit in awareness -- a conclusion that should only be reached, if at all, when all other explanations have been exhausted?   We should in the first instance attempt to remedy communication problems and only then decide whether awareness is irrecoverable.

Where the criteria state that persistent vegetative state may be diagnosed if no evidence is shown of "sustained, reproducible, purposeful, or voluntary behavioural responses to visual, auditory, tactile, or noxious stimuli" therapists know that there are a number of problems with these requirements. "The ability to generate a behavioural response fluctuates from day to day and hour to hour, and even minute to minute, depending on fatigue factors, general health of the patient and the underlying neurological condition." It takes considerable skill in getting them into the optimal condition to be able to communicate.  Many patients who are misdiagnosed as being in the vegetative state are blind or have severe visual handicap; thus lack of eye blink to threat or absence of visual tracking are not reliable signs for diagnosing the vegetative state. 

The list of things that might interfere with communication includes such factors as contractures, medication, motivation, depression, fatigue, position, long- and short-term changes in muscle tone, and stress -- stress that would be maximised in test situations where the patient is asked to perform on command (as in Alice in Wonderland -- "Give your evidence," said the King; "and don't be nervous, or I'll have you executed on the spot.")  Dyspraxia, the condition where one is able to perform a movement only on condition that one doesn't think about it, is also a recognised hazard in AAC. 

Given the uncertainties inherent in the diagnosis of persistent vegetative state, AAC intervention should precede diagnosis rather than vice versa.  Indeed, intervention aimed at establishing communication should be mandatory for this population, as non-speech communication strategies now available may be able to make use of controlled movements not evident at a traditional neurological examination. Andrews et al report that in their unit "the patient's awareness is nearly always identified first by the occupational therapists ... and only later is communication achieved by the other members of the team" and relate this to the patients' severe physical impairments and the need for appropriate positioning and adaptive equipment to elicit responses.

Everyone who has been diagnosed as being in a persistent vegetative state, no matter how long ago the diagnosis was made, should have a non-speech communication assessment given by a specialist multi-disciplinary team.

These topics are covered in more detail here.  Or give DEAL a call.