Original ArticlesLife expectancy and median survival time in the permanent vegetative state
Introduction
The vegetative state (VS) has been described as a condition of complete unawareness accompanied by sleep-wake cycles and at least partial preservation of hypothalamic and brainstem functions [1]. If present for 1 month or more, the condition has been described as a persistent VS. Recovery of consciousness from a post-traumatic VS is rare after 12 months and is rare after 3 months in the case of a nontraumatic VS [1]. Such persons are considered to be in a permanent VS. The prevalence of persons in the VS in the United States has been estimated at 4,000-10,000 children and 20,000-35,000 adults [1].
The duration of survival in the VS has been extensively studied [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. The issue is important for planning the resources needed to care for a given individual and is a factor in assessing the national overall cost of care of persons in the VS. It is well known that life expectancy in the VS is substantially reduced; what is much less clear is by how much and how the result is affected by factors such as the patient’s age and need for special assistance or care.
The Multi-Society Task Force on the Persistent Vegetative State [1] summarized the duration of survival time thus: “… life expectancy ranges from 2 to 5 years; survival beyond 10 years is unusual.” However, this statement needs considerable qualification and is overly pessimistic in many cases:
- 1.
The statement reflects a widespread confusion over the terms median survival time and life expectancy. The former is the time at which half of a cohort will have died; the latter is the arithmetic mean of the survival times [16]. In high-risk groups, such as patients in the VS, the life expectancy is considerably longer than the median survival time [16]. In the great majority of studies of persons with disabilities the measure reported is actually the median survival time rather than life expectancy (the mean). The life expectancy is more difficult to compute because it is based on a life table and requires mortality rates at all ages [17]; it may also be less useful clinically, because it is sensitive to a few individuals with exceptionally long survival times.
- 2.
Many of the commonly cited studies are 10-20 years old, and do not reflect the technologic advances that have been made in the care of the VS patient [6], [7], [13], [15]. The authors will return to this point.
- 3.
Virtually all the studies demonstrate a very high mortality rate during the first year after the onset of the VS [1], [8], [9], but the mortality rate falls appreciably for patients who survive this initial period. In consequence, a patient who has been in the VS for 1 year or more has a greater median survival time than one who has just entered the VS. It is the latter that has generally been reported.
- 4.
The populations studied in some of the reports consist of persons who are elderly or in infancy. The life expectancy of such persons cannot be assumed to apply to adolescents or young adults.
- 5.
It is possible that life support has been withdrawn from some persons in the VS [2]. Data are difficult to obtain, but in one study of patients who had a locked-in syndrome [1] for more than 1 year, 81% survived at least 5 additional years [4], [5]. This information is noteworthy because although locked-in syndrome resembles the VS in some respects, withdrawal of support would presumably never be considered.
In a study of 849 patients in the VS, Ashwal et al. [3] considered the effect of age and other factors on duration of survival. They reported median survival times of less than 5 years for infants less than 2 years of age but almost 10 years for patients older than 18 years of age. The median survival times reportedly decrease for more elderly patients with severe traumatic brain injury [14], [18]. There do not appear to be other published studies of the effect of risk factors on survival in the VS, perhaps because this requires larger samples than have generally been available. As a result the wide disparities in published reports with respect to the populations studied and the survival rates reported are not well understood.
The present study is based on a large group of persons in the VS, which permitted the authors to take into account several important risk factors simultaneously. Factors considered included etiology, the need for special equipment (gastrostomy and ventilator dependence), the time since the onset of the VS, and the secular trend (systematic change with respect to year of onset). The authors focused on the period beginning 1 year after onset of the VS. By this time the condition can be considered permanent in almost all patients. The authors’ purposes were to determine what effect these four risk factors, singly or in combination, have on the duration of survival in the VS and to develop a procedure for estimating the median survival time and life expectancy for a patient with a given profile of risk factors.
Section snippets
Patients and instrument
The authors reviewed data collected from the Client Development Evaluation report (CDER) [19] from January 1981 to December 1996. A CDER is filled out approximately annually for all 194,168 persons with neurologic deficits or other developmental disabilities who have received medical care or other assistance from the State of California. The CDER includes 261 items, including demographic information, etiology, associated medical conditions, level of motor functioning, self-care, and cognitive
Results
Table 1 presents the data on the 25,961 person-months (drawn from 1,021 patients in the VS) for age, calendar year, and other factors. Table 1 also provides the death rates per 1,000 person-years for each item. These mortality comparisons are crude, or univariate, in that no adjustment was made for the effect of other factors.
Table 1 reveals that 14% of the data were derived from infants younger than 2 years of age and that the mortality rate during this time was a high 452 deaths per 1,000
Discussion
The results of the present study reveal that the life expectancy of patients who have been in the VS for 1 year or more is greater than has generally been thought. Although life expectancies in the range of 2-5 years have been previously cited [1], the authors obtained life expectancies of 10-12 years for patients 15 years of age. The life expectancy will be still higher if the patient is fed orally. There are several reasons for the common underestimation of life expectancies in children and
Acknowledgments
Provision of data from the California Departments of Developmental Services and Health Services is gratefully acknowledged. The authors also thank James White for advice and help with the data.
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