One in five Americans dies in the intensive care unit (ICU) or shortly after an ICU stay. Regardless of the precise age threshold used to define “elderly,” it is clear that a sizeable proportion of ICU patients are older adults. In the United States, those aged 65 years or older constitute nearly 50% of ICU admissions, a percentage which will grow considerably with the aging of the population. While the proportion of elderly ICU patients maybe higher in the United States than in other countries, most developed countries have seen substantial ICU use by patients older than age of 65 years. Importantly, most studies support that age alone is not an independent predictor of outcome in the ICU and that age should not be used as a criterion for determining which patients can “benefit” from intensive care. Rather, the key issue is the reversibility of the acute illness in the context of the overall health of the patient.

As a group, the elderly present with a unique set of challenges and opportunities for critical care providers. Many of these are well-defined and known, while others are poorly defined and relatively understudied. In this chapter, we briefly review some of the physiologic changes associated with aging and their implications for intensive care. We discuss some of the common admitting diagnoses and associated conditions seen in elderly patients and present data about outcomes of intensive care in the aged. We then explore interventions that may improve outcomes of intensive care, not only for patients, but for their loved ones as well.

Much has been written about the physiology of aging and the reader may refer to the Chapters in Part IV on organ systems for more detail for a thorough review of the topic. Rather than duplicate what has already been written, we focus on some of the key physiologic changes associated with aging and their implications for intensive care. These changes can be summarized as a gradual decline in organ function and physiologic reserve with an increased prevalence of chronic disease and vulnerability to disease.

The aging cardiovascular system can affect critical illness in two ways. The first is through increased prevalence of cardiovascular disease, which may be the primary reason for presenting to the ICU or a complicating factor when a patient with a noncardiovascular admitting diagnosis subsequently develops acute cardiovascular illness, such as cardiac ischemia. The second way cardiovascular disease can affect critical illness is through decreased cardiac reserve. Though this decrease may not be sufficient to alter daily activities in otherwise healthy subjects, the acute “stress test” of critical illness is often sufficient to make it manifest.

Maximal heart rate, ejection fraction, and cardiac output decrease with age, as does the responsiveness to sympathetic stimulation. The aging heart is therefore somewhat limited in its ability to increase cardiac output in response to stress, relying primarily on increased filling and stroke volume, rather than increased heart rate. This leads to greater preload dependency and amplifies the cardiac output compromising effects of hypovolemia. However, because of age-related stiffening of the ventricles, diastolic dysfunction also becomes common, increasing the risk of pulmonary edema with overly aggressive fluid resuscitation. Ventricular stiffening results in an increased reliance on “atrial kick” for diastolic filling and poor tolerance of atrial fibrillation. Taken together, these changes mandate careful attention to volume status and control of atrial arrhythmias.

Pulmonary function gradually declines with age due to changes in the lung and chest wall. Vital capacity, or the maximum amount of air that can be exhaled after a maximum inhalation, decreases, as does the speed with which it can be exhaled. Because of ventilation–perfusion mismatching and increased airway closure, the oxygen content of arterial blood decreases with a resultant widening the alveolar-to-arterial oxygen gradient. In other words, less of the oxygen that is delivered to the lung is taken up by the body. The sum of these changes leaves elderly subjects less able to respond to the increase respiratory requirements of critical illness even in the absence of overt respiratory pathology, such as chronic obstructive pulmonary disease.

There is a significant decline in renal function with aging, including decreased renal blood flow, glomerular filtration rate (GFR), and creatinine clearance (CrCl). Urine concentrating and diluting ability also decrease, leaving the elderly patient less prepared to deal with electrolyte and volume status changes. Elimination of renally excreted drugs decreases in parallel with GFR. Approximations of GFR, such as CrCl, should therefore be used to adjust the dosage of these medications. A variety of equations can be used to estimate CrCl, with the Cockcroft and Gault equation most commonly utilized:

In this equation, Scr is serum creatinine and IBW the ideal body weight. For males, IBW = 50 kg + 2.3 kg for each inch over 5 feet; for females, IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.

Age-related changes in hepatic metabolism are much more difficult to predict. Unlike renal function, there is no measure to assess hepatic metabolism. Put simply, hepatic elimination of drugs is either reduced or unaltered. Host factors, such as blood flow, concurrent drug use, nutritional status, gender, disease states, and genetic differences in enzymatic activity, result in considerable metabolic variability from patient to patient. In the setting of known hepatic insufficiency, such as cirrhosis, clinicians should either avoid or reduce the dosage of hepatically eliminated drugs. In such patients, clinicians should also be on the watch for coagulation abnormalities and hypoalbuminemia, the latter of which may require reduced dosing for drugs that are highly albumin bound.

Aging is associated with significant changes in immune function that may have important implications for elderly ICU patients. The term “immunosenescence” has been used to describe these changes, which include unresponsiveness, hyporesponsiveness, or aberrant responsiveness to tissue damage and/or infection. With advancing age, T and B lymphocyte compartments of the immune system deteriorate progressively while the respiratory burst of macrophages and neutrophils becomes impaired rendering them less able to destroy bacteria. This leaves the elderly less responsive to vaccinations and more prone to developing invasive bacterial infections, whether community- or hospital-acquired. Furthermore, aging brings an imbalance of pro- and anti-inflammatory cytokines, leading to either inadequate or overabundant response when the system is challenged. As such, older subjects may not be able to adequately activate the immune system or stop it once it is started. Whether these cytokine imbalances make the elderly ICU patient more likely to develop cytokine-mediated organ dysfunction in the setting of tissue damage or infection is not known, though it seems likely.

In addition to organ system changes, aging brings about a gradual decrease in lean body mass and total body water with an increase in body fat. These body composition changes lead to changes in volume of distribution for many drugs. Fat soluble drugs, such as the sedative propofol, may have an increased volume of distribution, with fatty tissues serving as a slowly clearing drug reservoir once the medication is stopped. Water-soluble drugs, on the other hand, may have a decreased volume of distribution, with a potential need for loading dose reductions. For an excellent review of pharmacokinetics in the elderly, the reader is referred to Mayersohn. Changes in body composition and physical activity also lead to a decrease in resting energy expenditure. Even so, risk of protein-calorie malnutrition increases, especially during acute illness, highlighting the importance of early nutritional support.

Table 19-1 lists some of the more common ICU admitting diagnoses seen in the elderly, many of which represent exacerbations of chronic conditions or diseases to which the elderly are particularly vulnerable. Rather than focusing on management principles of each disease, which are well covered in just about any critical care text, we review two quintessential diseases of the elderly, community-acquired pneumonia (CAP) and severe sepsis.

Pneumonia is often called the old man’s friend because, as pointed out by Sir William Osler more than 100 years ago, pneumonia is a frequent, nonpainful, lethal event in elderly patients. Since Osler’s time, there have been considerable advances in the management of pneumonia, not the least of which is the discovery of antibiotics. Nevertheless, CAP remains common and is still one of the leading causes of hospital admission and death throughout the world. In an analysis of 150 000 elderly Medicare recipients hospitalized with CAP in the first quarter of 1997, Kaplan and colleagues found that almost half of all elderly patients admitted for CAP die in the subsequent year, with most deaths occurring after hospital discharge. One of three elderly patients who survived hospitalization for CAP died in the year following hospital discharge. Their data confirm Osler’s notion and show that even today, with many preventive and therapeutic measures, there is a high risk of death in elderly patients discharged from the hospital after an episode of CAP. These data have important implications for patient prognostication, family counseling, and medical decision making, such as whether to continue life support and aggressive medical care. They also highlight the fact that hospital mortality is not an appropriate outcome measure for studies in elderly patients with CAP, since beneficial or detrimental aspects of interventions may not manifest within this time frame. Given the overall poor prognosis that CAP portends for the elderly, preventative measures, such as pneumococcal and influenza vaccination and smoking and alcohol cessation, will remain key.

Severe sepsis is a common, expensive, and frequently fatal condition, with as many deaths annually as those from acute myocardial infarction. It is especially common in the elderly and is likely to increase substantially as the U.S. population ages. Angus and colleagues examined the incidence, cost, and outcome of severe sepsis in the 1995 hospital discharge records from seven large states. The authors found that the incidence of severe sepsis increased >100-fold with age (0.2/1000 in children to 26.2/1000 in those >85 years old). The most commonly identified sites of infection were respiratory, genitourinary, abdominal, and wound/soft tissue. Mortality was 28.6%, or 215 000 deaths nationally, and also increased with age, from 10% in children to 38.4% in those >85 years old. Women had lower age-specific incidence and mortality, but the difference in mortality was explained by differences in underlying disease and site of infection. Average costs per case were $22 100, with annual total costs of $16.7 billion nationally. Incidence was projected to increase by 1.5% per annum.

The observation that sepsis is a disease of the elderly mandates consideration of the appropriateness of care, including determination of patient preferences. Data suggest that there are already differences in the aggressiveness of treatment in the very old, with lower length of stay, ICU use, and hospital costs in those aged >85 years. Yet, aggressive care is not necessarily futile in the elderly, and the majority of elderly septic patients survive to hospital discharge. Unfortunately, there are limited data on postdischarge survival or quality of life after sepsis in the elderly. Such information will be crucial in determining optimal healthcare policy as the U.S. population ages and the number of cases of sepsis increases.

In addition to age-related changes in physiology, there are a number of associated conditions that may complicate the care and management of critically ill elderly patients (Table 19-2). Atypical presentations of common medical conditions, such as myocardial infarction and CAP, are common in the elderly, which may lead to delayed or incorrect diagnoses and which mandate broad initial differential diagnosis lists. Anemia may be preexisting or a consequence of critical illness. Current guidelines recommend restricting red blood cell transfusion to those patients with hemoglobin values of ≤ 7 g/dL, as long as active bleeding or ischemia is not present. Drug-resistant organisms are increasingly encountered, especially in nursing home residents or those who are frequently hospitalized. While it is important to avoid antibiotic overuse, careful attention to risk factors and local resistance patterns should guide antibiotic selection.

The proportion of elderly patients who are undernourished is high and undernutrition has serious health implications in the ICU, including immune dysfunction, poor wound healing, and increased mortality risk. Dysphagia, poor dentition, swallowing disorders, and constipation not only put patients at risk of aspiration, but may also significantly impair nutritional support measures. Polypharmacy is widespread, increasing the likelihood of drug interactions and life-threatening side-effects. Medication lists should therefore be “trimmed” regularly and reconciled with each care setting transition.

Pressure sores may be a reason for admission, such as when they are a source of infection, or a complication of care, especially if skin care is not meticulously addressed. Skin integrity can be further compromised by urinary or bowel incontinence, though collecting devices, such as urinary catheters, may exacerbate other conditions, such as delirium. Vision and hearing difficulties are frequent and efforts should be made to avoid sensory deprivation due to misplaced glasses or hearing aids. Alcoholism is present in around 10% of ICU patients and even more common is certain patient populations, such as those admitted for trauma. Early recognition of alcohol abuse and dependence is essential and should prompt consideration of several alcohol-specific diagnoses that have important prognostic and therapeutic implications, including alcohol withdrawal, cardiomyopathy, arrhythmias, and electrolyte disorders.