Department of Anesthesiology and Resuscitation, Polenov Research Neurosurgical Institute, Saint Petersburg, Russia
A number of patients with impaired CNS function, which is defined as a vegetative state, is growing constantly all over the world. Absence of a precise definition of a vegetative state as a version of recovery from coma in the international classification of diseases hampers obtaining exact data on a number of cases. Criteria, proposed by the American Association of Neurologists in 1992, put in certain order both the rate analysis and estimation of efficacy of treatment methods. But it was only the first step.
A vegetative state appears to be caused by complete dissociation between an awakening response and all other components of consciousness. Versions of primary CNS injury, resulting in a vegetative state, as well as disorders of vital activity are diverse. Despite outward similarity of clinical manifestations, they are caused by different pathophysiologic mechanisms. Revealing of these mechanisms can promote improvement of treatment methods. Unfortunately, today they are limited to general care and correct nutrition of patients. It is evident, that some cases recover from a vegetative state. Ways of prognosticating a recovery term, an effect of applied methods on it and, at last, a mechanism of consciousness restoration are not understood up to the end.
There were 34 cases, meeting international criteria of a vegetative state, who were examined and treated in the Resuscitation Department of the Polenov Research Neurosurgical Institute in 1996-2004. Coma, which turned into a vegetative state, was caused by craniocerebral trauma (15 cases), posthypoxic encephalopathy (14 cases), spontaneous cerebral subarachnoid hemorrhage (5 cases). Hypoxia developed as a result of cardiac arrest during intervention in patients without intracranial pathology (6). Besides, this group included 3 cases with mechanical asphyxia, 1 female patient with status asthmaticus of long standing and 1 female patient with episodes of rhythm disorders, accompanied by repeated asystolia. Duration of a vegetative state was more than 30 days in all the cases. As for the patients with subsequent restoration of consciousness, the minimum and maximum periods of a vegetative state were 31 and 277 days respectively. The age varied from 5 up to 72 years.
The patients underwent complete neurosurgical investigation, including daily examination by a resuscitator and neurologist, use of different methods of neuroimaging, transcranial Doppler for estimation of cerebral blood flow, laboratory tests, examinations by other specialists. CT and MRI findings were indicative of diffuse atrophy with secondary widening of the ventricular system and subarachnoid spaces, different cysts (patients with sequelae of craniocerebral trauma). Presence of signs of hypertensive hydrocephalus demanded performing liquor-shunting operations in 6 cases. PET with fluorodesoxyglucose was used in 5 patients; t was indicative of metabolism reduction the cortex and subcortical structures by 20-50% from normal values.
All the patients had no somatic disorders, which could be considered a cause of impaired cerebral function. Biochemical investigations of blood, urine showed no considerable deviation in metabolism of proteins, lipids, carbohydrates and electrolytes. There was normalization of such intracellular enzymes as creatine phosphokinase, ALT, AST, LDH, amylase, alkaline phosphatase in blood plasma. Retrospective analysis of obtained data showed almost the same clinical course of a vegetative state in the patients with subsequent restoration of consciousness and the cases, whose state remained unchanged. Results of electrophysiologic studies were more informative. Scalp encephalograms revealed the following patterns of spontaneous bioelectric activity: 1) a "flat" EEG pattern - 11 cases, 2) a stem slow-wave EEG pattern - 10 cases (distant synchronized teta- and delta - activity or teta- and delta-activity - 6 patients), 3) a pattern of disorganized polymorphic bioelectric activity - 12 patients.
Our data agreed with those of literature. Use of a pharmacological test, elaborated by us, in 22 cases demonstrated, that administration of benzodiazepines resulted in appearance of rapid forms of activity or rhythms of alpha- and beta-ranges in some cases, including those with a flat EEG pattern. We observed it in 12 patients. According to the data of retrospective analysis, the cases with EEG changes, watched during applying the above test, achieved a state of minor consciousness later on. The patients remained in a vegetative state, if such changes were absent. Our method of treatment was based on the following hypothesis: changes of EEG during applying the above pharmacologic test reflect appearance of a new level of brain functioning, irrespective of activity of a stable pathologic system. One can suppress the activity of a pathologic system by fixing this level.
Thus, according to our data, the main method of revealing an active and stable pathologic system, formed within CNS after brain injury and manifesting itself in a vegetative state, is scalp EEG, which is used under conditions of the described pharmacologic test. We do not possess a sufficient number of observations for differentiation of patterns of altered bioelectric activity from the point of view of their dependence on outcomes of a vegetative state. It seems, that further accumulation of data will allow to carry out more exact prognostication and planning of treatment.