PVS may occur in patients with severe brain damage from HYPOXIA or injury. Patients do not display any awareness of their surroundings, and are unable to communicate. Sleep alternates with apparent wakefulness, when some reﬂexes (see REFLEX ACTION) may be present: for example, patients’ eyes may reﬂexly follow or respond to sound, their limbs can reﬂexly withdraw from pain, and their hands can reﬂexly grope or grasp. Patients can breathe spontaneously, and retain normal heart and kidney function, although they are doubly incontinent (see INCONTINENCE).
For a diagnosis of PVS to be made, the state should have continued for more than a predeﬁned period, usually one month. Half of patients die within 2–6 months, but some can survive for longer with artiﬁcial feeding. To assess a person’s level of consciousness, a numerical marking system rated according to various functions – eye opening, motor and verbal responses – has been established called the GLASGOW COMA SCALE.
The ETHICS of keeping patients alive with artiﬁcial support are controversial. In the UK, a legal ruling is usually needed for artiﬁcial support to be withdrawn after a diagnosis of PVS has been made. The chances of regaining consciousness after one year are slim and, even if patients do recover, they are usually left with severe neurological disability.
PVS must be distinguished from conditions which appear similar. These include the ‘LOCKED-IN SYNDROME’ which is the result of damage to the brain stem (see BRAIN). Patients with this syndrome are conscious but unable to speak or move except for certain eye movements and blinking. The psychiatric state of CATATONIA is another condition in which the patient retains consciousness and will usually recover.