Study Guide - Life Expectancy
30 August 2018
The only true statement about a life expectancy estimate for the Court is that it is bound to be wrong. There are so many variables to take into account in coming to a life expectancy, particularly in someone with a severe disability, that an accurate prognosis is next to impossible. Fortunately, the English and Welsh, and increasingly the Scottish, systems now rely on Periodical Payment Orders (PPOs) which to large extent have done away with the need for a life expectancy estimate as the agreed sums will be paid for life no matter how short or long that life may be. Nevertheless, PPOs are not compulsory and indeed insurance companies will often still need a life estimate in order to work out their potential financial exposure. Thus the art (and not the science) of life expectancy is still alive and well. Over the years the debate has been rather polarised with some experts simply regurgitating the statistical database estimates from Professor David Strauss and colleagues in California, whilst other experts have made the point that life estimates have to be based on clinical examination rather than a relying on a less personalised statistical analysis. However, in recent years it seems to be generally accepted that the two approaches need to be amalgamated. An expert needs to have a good knowledge of the underlying statistical work whilst being prepared to adjust that statistically based estimate according to clinical circumstances of a given individual. This does seem a sensible approach.
Professor David Strauss and his colleagues in California have dominated this field for many years. There are have been other statistically based estimates, particularly in the context of cerebral palsy, but Strauss has produced most of the work on the topic. He is certainly to be congratulated on being a pioneer in this field. However, there are some valid concerns about his statistical analysis.
First, from the point of the UK legal systems, his work is based in California which has a different health system and, frankly, community care in the United States is really quite poor compared to the UK. Thus his population and more particularly the care given to the disabled people are different and we are not really comparing like for like when we use the American statistics. It is also worth bearing in mind that like any statistical database the more refined the analysis the less the number of patients in each category. Thus it can be reasonably said that statistical analysis in a large group, (for example, a cerebral palsy male aged 30 years who lifts his head or chest and is tube fed), certainly has statistical validity but a more refined examination of the given individual may indicate, for further example, that he may be able to lift his head in certain circumstances or at some times and not others or he may need tube feeding only for certain meals or certain times of the day or there could be variability according to medication timings, etc. Thus in my view reliance on the Strauss tables should, and indeed must, be open to clinical interpretation.
The Strauss database is probably most useful when there are large populations, such as cerebral palsy and traumatic brain injury. It becomes somewhat less useful when there are smaller populations, such as vegetative state and spinal cord injury. The key Strauss papers are outlined in the Further Reading section below and the reader is also referred to the Strauss, Shavelle and Brooks website – www.lifeexpectancy.org.
If we accept that there needs to be a clinical interpretation of the statistical analysis then what are the main factors that reduce life expectancy in the neurologically disabled population? There is consensus in literature that there are five key factors.
- 1. Mobility
This is definitely the key factor and is confirmed in virtually all the literature on the subject. Basically, individuals who can walk survive longer than those who cannot walk. The risks of mobility are largely related to the potential to develop pressure sores but also mobility is a cause of osteoporosis which in turn leads to a higher risk of limb fractures with consequent complications, particularly in the ageing population. There is almost certainly a graduated effect according to the degree of immobility. As an example, a paper by Hutton and colleagues (see Further Reading) demonstrated that 30 year survival in children with cerebral palsy was 97.5% for those with some mobility compared to 42% for those who were wheelchair dependent. The same trend applied to older people with cerebral palsy.
2. Swallowing Problems and Tube Feeding
There is good literature that people who require tube feeding are at risk of earlier death. This may, of course, be a simple marker of the degree of underlying brain damage. There is, once again, a graduated effect in that those attempting to finger feed but needing assistance have a higher mortality than those who are able to feed themselves.
Epilepsy is definitely a risk factor for earlier death. There is a small risk of dying during a fit and a slightly higher risk of dying in between fits in the so-called Sudden Unexpected Death in Epilepsy (SUDEP) syndrome. Increased mortality is probably limited to those with more severe epilepsy that is poorly controlled. Fortunately, modern anticonvulsant drugs mean that around 80% of people with epilepsy are fully controlled on a single anticonvulsant drug and a further 10% reasonably well controlled on two or more drugs. It is important to take into account not only the frequency of the seizures but the type of epilepsy with generalised seizures obviously carrying higher mortality than other "lesser" types of seizures, such as absences.
It is also clear that individuals who are incontinent have a risk of earlier death, probably as a result of urinary tract infections, bladder stones, longer term kidney problems, increased risk of pressure sores from macerated tissue, and septicaemia.
5.Cognitive and Intellectual Function
Most of the risks of earlier death are related to the physical consequences of disability but it is also known that the degree of cognitive and intellectual dysfunction seems to have a significant effect on life expectancy. As an example, Hutton and Pharoah (see Further Reading) demonstrated that normal or mild "mental disability" was associated with a 97.7% 30 year survival compared to just a 61.9% 30 year survival in those with severe cerebral palsy.
These are the main risk factors but obviously there are many others that may occur in individual cases. Individuals with hydrocephalus seem to be at a higher risk. Certainly people with severe scoliosis (usually children with cerebral palsy) are also at a risk of respiratory impairment and consequent risk of pneumonia. People with intracranial shunts are also at risk. One study has shown an adverse effect on life expectancy in those with visual problems and also hearing problems. This may reflect the underlying degree of brain damage.
The clinician needs to take into account lifestyle factors. Sadly, there is an increased risk of excess alcohol after brain injury and spinal injury as well as an increased risk of drug abuse and suicide. Other factors can sometimes have a bearing, such as employment status, marital status, degree of community integration and income. An important study by Krause and colleagues (see Further Reading) clearly showed an increased mortality for those at the poorer end of the income spectrum who were not well integrated into their local community.
Normal Life Expectancy
Experts need to take into account the expectation of life in the "normal" population and such figures can be extracted from the Facts and Figures annual publication. These are tables that project life expectancy in the whole UK population and obviously are a key starting point for life estimates. Generally, the Courts accept these figures as a baseline though it is worth noting that there is wide variation in life expectancy according to socioeconomic status, area of residence and other obvious health and lifestyle factors such as smoking, drug use, obesity and alcohol intake as well as physical fitness and diet. There are tables and figures available for most such factors but unless an individual falls well outside a reasonably accepted "normal" range then the Courts will generally not allow for an adjustment of the baseline projected life expectancy figure.
Life expectancy is a complicated and inaccurate science and it is probably more accurate to call it an art form. However, at the present time, a life estimate, particularly in the context of traumatic brain injury or cerebral palsy, needs to depend on an understanding of the statistical databases available, but a sensible clinician will adjust those tables according to the clinical characteristics of the individual.
Brooks JC, Strauss DJ, Shavelle RM, et al.Recent trends in cerebral palsy survival. Part I: period and cohort effects.Dev Med Child Neurol; 2014; 56: 1059-1064
Brooks JC, Strauss DJ, Shavelle RM, et al.Recent trends in cerebral palsy survival. Part II: individual survival prognosis.Dev Med Child Neurol; 2014; 56: 1065-1071
Brooks JC, Shavelle RM, Strauss DJ, et al. Long-term survival after traumatic brain injury. Part I: External validity of prognostic models. Arch Phys Med Rehabil 2015; 96: 994-999
Brooks JC, Shavelle RM, Strauss DJ, et al. Long-term survival after traumatic brain injury. Part II: Life expectancy. Arch Phys Med Rehabil 2015; 96: 1000-1005
Hutton JL, Pharoah PO.Effects of cognitive, motor, and sensory disabilities on survival in cerebral palsy. Arch Dis Child 2002; 86: 84-9
Krause JS, DeVivo MJ, Jackson AB. Health status, community integration, and economic risk factors for mortality after spinal cord injury. Arch Phys Med Rehabil 2004; 85: 1764-1773