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Source: Strauss DJ, et al. Life expectancy of children in vegetative and minimally conscious states. Pediatr Neurol 2000; 23:312-319.
It has been known for a number of years that children in a vegetative state (VS) have reduced life expectancies than do normal children (Pediatr Neurol 1994;10:27-33). What accounts for this? Could the presence of consciousness, even if minimal, play a role in improving survival?
In order to to approach this question, this study from Ashwal and associates compared cohorts of children (3 years old at time of study entry) initially in PVS, immobile minimally conscious state (iMCS) and mobile minimally conscious state (mMCS) with respect to survival over a 10-year period. Ashwal et al’s group used detailed database information collected by the California Department of Developmental Services (CDDS) over the 10-year period from January 1988 to December 1997. The CDDS maintains Client Development Evaluation Reports (CDERs) which provide information regarding 261 variables. By using selected variables in the CDER reflecting mobility, level of independence, perception and language, Ashwal et al were able to develop a 15-item consciousness index (see Strauss et al’s article for details). Patients are operationally defined to be in VS if they scored the lowest grade on all items in the index, but in MCS if they scored better than the lowest score on any of the 15 items. Finally, patients in MCS were termed "mMCS" if they were minimally conscious but had either hand use, arm use, or ability to roll and sit. Otherwise they were termed "iMCS."
Strauss and associates found that patients in VS had extremely similar long-term survival rates to iMCS. Mobile MCS patients had improved long-term survival compared to either VS or iMCS patients. Among patients with VS and MCS, there was variability in mortality rate according to etiology, with mortality risk increasing in the order acquired (including traumatic) brain injury < perinatal/genetic < non-specified < degenerative. Strauss et al provide odds ratio calcuations. Using these, one can, for example, compute that a patient with degenerative disease in VS has approximately a four-fold higher mortality rate than a patient with traumatic brain injury in a mobile MCS.
This paper highlights several factors that may be important in determining mortality rates of children with severe impairment of consciousness. Etiology of impaired consciousness is clearly important. The level of impairment of consciousness (i.e., complete vs incomplete) appears to be less important than the presence of some degree of mobility. As Strauss et al point out, the reasons for improved survival in mobile patients are unknown. They also point out that mobile patients are more likely to have intact swallowing mechanisms, gag reflex, and improved pulmonary toilet, all of which are associated with improved survival. It might be interesting to compare survival of mobile and immobile MCS patients to fully alert patients with quadriplegia in order to test this idea.
One potential clinical implication of this study is that efforts should be made to improve spontaneous mobility in patients in MCS, as this seems to be associated with improved long-term survival. —Rosario Trifiletti