Caring for the aging population is one of the most important challenges of the twenty-first century. A key component of medical care delivery in the elderly is the provision of critical care services.
In addition to chronologic age, disability, comorbidity, and frailty are components of defining the elderly population. Frailty is a clinical syndrome characterized by multiple factors, including weight loss, fatigue, weakness, low activity level, slow motor performance, balance and gait abnormalities, and cognitive decline. A combination of age, function, and social definitions is key to precisely defining the elderly population.
The demographics of the global and US populations have changed dramatically over the course of the last two centuries as a consequence of demographic transition, which defines a transition in a population from high birth and death rates to low birth and death rates as a result of economic development.
The world population reached 7.3 billion in 2015 and has aged at unprecedented rates. By 2050, the number of elderly in the world will, for the first time in history, be greater than the number of young individuals.
The sharp increase in the US birth rate between 1946 and 1964 is termed the baby boom. This has resulted in a drastic shift in the age distribution of the population. In 2015, the median age in the United States was 37 years, and it is estimated that this will increase to 42 years by 2050. Conversely, the total fertility rate in the United States has been declining and was 1.89 in 2015. Therefore, the growth rate of the elderly population is far higher than that of the younger population.
Chronic medical conditions are expensive to treat. Multimorbidity is the presence of two or more chronic diseases and is common in the elderly, with a prevalence of 40 to 80 percent. It has a substantial impact on mental health, quality of life, and overall health outcomes and is associated with a significant increase in mortality. Disability in the elderly may have an even greater impact on mortality than multimorbidity.
The elderly population comprises an increasing proportion of patients admitted to intensive care units (ICUs), and the mortality rate for these patients is high. Equally important is the significantly decreased physical function and overall health of ICU survivors.
The United States spent nearly $3 trillion in healthcare expenses in 2014, which is 17.5 percent of the gross domestic product (GDP), a percentage higher than that of any other country. The elderly use a large portion of the total healthcare expenditure in the United States due to the high hospitalization and institutionalization rate. Healthcare spending increases proportionally with age.
Areas of opportunity for improvement in the allocation of healthcare resources to the elderly include enhanced awareness and education, studies that precisely define and stratify the elderly, and changing focus from survival to mitigation of cognitive impairment, improvement in quality of life, and an increase in functional autonomy. Identification of the best approach to provide multidisciplinary care ranging from surgical and critical care to palliative care in a manner that enhances communication and achieves desired outcomes will improve the quality of care and reduce healthcare expenditures.
Caring for the aging population is one of the most important challenges of the twenty-first century. Media outlets, political figures, books, and television programming frequently elaborate on the difficulties the world will face as the age of the population increases . Studies also indicate that not only are people living to an older age, but they may also have an increased number of quality years, as defined by better cognitive function and self-perceived health at the end of life . Therefore, the aging population has become a topic that deserves attention from the medical community.
As the population age increases, so does the body of medical literature examining the best medical practices to care for the elderly. However, to understand the literature, we must first define the elderly population, evaluate the impact this population has on the medical system, and understand its significance in the current medical culture. A key component of medical care delivery in the elderly is the provision of critical care services.
In order to understand the unique complexities of the elderly patient, we must first define the elderly population. One way to define elderly age is based on lifespan. In nineteenth-century Britain, the Friendly Societies Act defined old age as “any age after 50.” At that time, the average life expectancy at birth was only 47.3 years. Therefore, population groups older than 50 years of age represented a minority of the population . Today, most epidemiologists would argue that the definition of the elderly should be fluid and adjusted in accordance with the ever-increasing life expectancy. According to the Centers for Disease Control and Prevention (CDC), the expected lifespan for Americans at birth in 2013 was 78.8 years, which is a two-year increase from the year 2000 . As healthcare continues to change and life expectancy continues to rise, it becomes necessary to use a metric other than chronologic age to define the elderly.
President Johnson passed the Medicare law under Title XVIII of the Social Security Act in 1965. Medicare aimed to provide health insurance to the elderly (people 65 years of age and older) regardless of their sociodemographic status . Because of the significant impact this act had on the medical world, and because of the large number of patients covered by Medicare, much of the medical literature defines elderly age using the chronologic age of 65 years or older. Medicare covered nearly 40 million elderly individuals in 2010 and financed an estimated 15.3 million hospital admissions in 2011, which accounted for almost 47 percent of the total inpatient hospital costs in the United States in 2011 .
According to the World Health Organization (WHO), 71 years was the average life expectancy of the global population in 2013. However, the average life expectancy in developing countries is as low as 50 years . Most developed countries use the age of 65 years as the cutoff to define an older person, but in developing countries this definition does not necessarily correlate.
Aging is a chronologic biologic certainty, but it is also subject to the social constructs of cultures. In developed countries such as the United States, chronologic age plays a paramount role. However, in developing countries, the change in social roles plays a far more important part in defining the elderly . In most developed countries, 60 or 65 years is the age of retirement and is therefore often the cutoff for the definition of old age. In contrast, in developing countries, where retirement is less common, social roles and loss of social station due to physical decline play a far more important part in dictating the definition of old age. Therefore, in developing countries, old age commences at the stage of life where one is no longer able to contribute to one’s assigned role in society .
In developed countries such as the United States, there has historically been inconsistent correlation between chronologic and physiologic age. Multiple attempts have been made to categorize patients as elderly based not only on their age but also on their functional status. Fried et al. distinguishes between disability, frailty, and comorbidity by defining frailty as a clinical syndrome characterized by multiple factors, including weight loss, fatigue, weakness, low activity level, slow motor performance, balance and gait abnormalities, and cognitive decline . While many studies have attempted to create an index to predict biologic age based on frailty, comorbidity, and disability, none have completely captured the complexity that defines the elderly patient . A study by Jacobs et al. evaluated a large cohort of elderly patients who had a favorable overall health profile at the age of 70 years but had progressive deterioration at the age of 78 years and older and more profoundly so at the age of 85 years and older . As a consequence of these data, many suggest that a cutoff of 70 years of age may be a better definition of the elderly; however, there is still a need for further research to differentiate between the aging process and disease morbidity .
Because of the varying perspectives pertaining to the definition of the elderly, most would agree that a simple characterization such as age or functional status does not answer the complex question of the definition of old age. It may be more appropriate to use a combination of age, function, and social definitions.
Demography comes from the two Greek words, dēmos, which means “the people,” and graphō, which means “measurement.” Historically, demography has been defined as the study of changes in human populations over time . The global population has changed dramatically over the last two centuries as a consequence of demographic transition. This concept, described by Warren Thompson, defines a transition in a population from high birth and death rates to low birth and death rates as a consequence of economic development . Pre-industrialized societies have high birth rates because children can contribute to individual household economy. In these societies, however, mortality remains relatively high. Accordingly, the population of the pre-industrialized society is predominantly young. Conversely, as countries begin to industrialize, death rates decline due to improved health and augmented resources. As a consequence, the populations of industrialized countries grow exponentially. Birth rates eventually decrease in post-industrialized societies given improved access to contraception, urbanization, and literacy and increased rates of employment in women. Subsequently, the age distribution in post-industrialized societies shifts to a predominantly elderly population .
According to the UN World Population Prospects in 2015, the world population reached 7.3 billion, an increase of nearly 1 billion over the last 12 years . It is estimated that the world population is growing at an average rate of 1.18 percent per year . Population growth has been particularly high in the least developed countries; continents with high fertility rates, such as Africa, have had the highest rate of population growth in the last decade (2.5 percent annually) .
Given the increased number of industrialized countries in the world, the population has aged at unprecedented rates. Predictably, over the last 10 years, life expectancy has increased globally by 3 years (from 67 to 70 years). The greatest increase in life expectancy occurred in Africa. However, this increase is still significantly lower than the North American life expectancy (60 versus 79 years) . As a result of increased life expectancy, the population group older than 60 years of age has had the largest annual growth rate at a global level (3.2 percent per year), nearly three times that of the population as a whole . In 2015, the United Nations reported that globally, there were 901 million people older than 60 years of age, which comprised nearly 12 percent of the world population. The United Nations estimates that by 2050, the number of elderly in the world will, for the first time in history, be greater than the number of young individuals.
The United States has seen similar changes in the age structure of its population. After World War II, there was a historic increase in the annual birth rate, with 3.4 million babies born in 1946, 20 percent higher than the year before. The sharp increase in the birth rate was maintained for nearly 18 years, until 1964, at which point there had been 76 million babies born . This sharp rise in the American birth rate has been termed the baby boom. As a consequence, the age structure of the population has been continuously and drastically shifting. In 2015, the United Nations reported that the median age in the United States was 37 years, seven years higher than that in 1980. It is estimated that the median age will continue to increase to 42 years in 2050. According to the most recent US Census of 2010, the median age in the United States varies substantially based on both geography and gender. Northeastern states have the highest and western states the lowest median age (39.2 versus 35 years, respectively). Women have the highest median age throughout the country . Accordingly, life expectancy in the United States has increased from 75 years in 1990 to 79 years in 2015.
In contrast, in United States the total fertility rate (average number of children per woman) has been slowly declining. In 2015, the total fertility rate in the United States was 1.9, 8 percent lower than that documented in 2005. It is estimated that the United States has one of the lowest fertility rates in the world . As expected, these data have substantial ramifications for the age distribution. According to the 2010 US Census, the population of Americans under 18 years of age comprised up to 24 percent of the population, with annual growth rates of 2.6 percent per year. In contrast, the 65 years of age and older population comprised only 13 percent of the total population but had a growth rate nearly six times higher than that of the population group younger than 18 years of age .
Many studies have documented the increased prevalence of chronic medical conditions and lower physiologic reserve in the elderly compared with their younger counterparts . The cost of treating chronic conditions is close to five times higher than that of nonchronic illnesses . Kodner et al. suggest that treatment of chronic diseases represents the highest-cost and fastest-growing segment of US healthcare . Multimorbidity, the presence of two or more chronic diseases, is becoming common among the elderly, with a prevalence of 40 to 80 percent, which is eight times higher than the rate seen in the younger than 19 years of age group . Cognitive impairment and cardiovascular disease are the most common disorders among the elderly. In the elderly population, the prevalence of chronic neurologic disorders increases proportionally with age, beyond that seen with cardiovascular disease, with the oldest-old (>85 years of age) having a prevalence of neurologic disorders as high as 36 percent . Many studies have demonstrated that multimorbidity has a substantial impact on mental health, quality of life [27, 28], and overall health outcomes in the elderly population . Multimorbidity in the elderly population has been associated with substantial increases in the risk of mortality, with some studies reporting risks as high as 53 percent . However, more important than comorbidity is the impact of disability on quality of life and mortality among the elderly. According to the most recent CDC estimates, nearly 36 percent of persons older than 65 years of age have evidence of disability . Several studies have demonstrated that disability plays an important role in mortality in the elderly. Landi et al. suggest that the effect of disability on the risk of death was higher than, and independent of, multiple comorbidities. However, the combination of both multiple comorbidities and disability greatly increases the risk of mortality in this population group .
The elderly population comprises an increasing proportion of the patients admitted to ICUs. Approximately one-half of all patients admitted to the ICU are over age 65, even though this same age cohort comprises only approximately 12 percent of the population . Despite advances in medical and surgical care, the mortality rate for elderly patients admitted to the ICU is unacceptably high. A study by Tabah et al. demonstrated that the one-year mortality rate was 67 percent in the subgroup of elderly patients being admitted to the ICU for unscheduled surgery . Consistent with these results, de Rooij et al. demonstrated that the one-year mortality rate for both medical and unplanned surgical admissions in the elderly was 89 percent .
Equally important is the consideration of how patients who survive their ICU admission will function after discharge. Roch et al. suggest that the two-year mortality rate of patients over 80 years of age who are admitted to the ICU remains unacceptably high compared with the general population. Approximately 50 percent of the elderly discharged from the hospital after their ICU stay were not be alive after two years. Moreover, the physical function and overall health of the survivors were significantly decreased compared with younger populations .