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Geriatric Anesthesia
Key Points
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The proportion of adults over age 70 has increased throughout the world with a corresponding increase in older surgical patients.
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Normal aging is associated with changes in physiology and an increase in many pathologic conditions.
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The number and impact of normal and pathologic conditions varies significantly across elderly individuals.
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Preoperative screening recommendations and guidelines for older patients can provide a useful starting point to evaluate and optimize care.
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Some important geriatric specific areas that are amenable to screening include: cognition, frailty, depression, and polypharmacy.
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Best intraoperative practices follow from an understanding of geriatric physiology and awareness of medications which are contraindicated in the older population.
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Postoperative care tailored to the needs of high-risk adults may benefit the highest risk patients such as palliative care consultation and delirium prevention units.
Acknowledgment
The editors and publisher would like to thank Drs. Frederick Sieber and Ronald Pauldine for contributing a chapter on this topic in the prior edition of this work. It has served as the foundation for the current chapter.
America is growing old. The number of Americans over age 70 has increased from approximately 15 million in 1975 to over 30 million in 2015, with a corresponding increase in both the percentage of Americans over age 70 and the median American population age ( Fig. 65.1A-C ). Similarly, worldwide, the number of people over age 70 has increased from approximately 130 million in 1975 to over 400 million in 2015, accompanied by similar increases in the percentage of people over age 70 and the median population age (see Fig 65.1B,C ).
(A) Population age trends in the United States. (B) Worldwide trends in population age over time. (C) Population percentage age >70 by decade.
The age-related population shifts have translated to similar changes in the population of patients undergoing anesthesia and surgery. In the United States alone, more than 16 million patients over age 60 underwent surgery in 2006. These profound shifts in the American population and the American surgical population have significant implications for anesthesiologists. First, most (though not all) diseases increase in frequency with age. Second, there are age-dependent physiologic changes in virtually every human organ system. These age-dependent physiologic changes typically result in a decrease in the physiologic and functional reserve capacity of each organ system. However, there is considerable variability in the extent of age-dependent changes across organ systems in individual patients, and considerable variability across older patients in the extent of these age-related changes. Indeed, a general principle of geriatric medicine is that as the population ages, the variance of virtually every physiologic measurement increases. Thus while older patients as a whole present additional challenges for perioperative management as a result of increases in comorbid disease and decreases in physiologic reserve, it is important to avoid overapplying these generalizations to individual older patients.
One potential reason that these generalizations apply to varying degrees among older patients is that aging itself involves a plethora of biological pathways ( Fig. 65.2 ) which proceed at varying rates across patients. For example, two 80-year-old patients may show very different telomere lengths, genetic mutation accumulation, and cumulative oxidative stress. Differences in these types of biologic pathways involved in aging have led many to refer separately to chronological age (reflecting the number of years of life) versus biologic age (reflecting the actual accumulation of changes in biologic processes involved in aging).
Molecular, cellular, and organ-level mechanisms of aging.
Redrawn from López-Otín C, Blasco MA, Partridge L, et al. The hallmarks of aging. Cell . 2013;153[6]:1194–1217.
In this chapter, we discuss common age-dependent physiologic and pathophysiologic changes, and their implications for the preoperative assessment, intraoperative management, and postoperative care of older adults. The significant increases in the age of the American population suggest that the perioperative management of older adults will likely become an increasingly large focus for anesthesiologists. Further, the significant increases in biomedical research expenditures focused on aging and older adults provide reason to hope that this research will lead to improved postoperative outcomes for older adults in the future.
Organ-Specific Age-Related Physiologic and Pathologic Changes
Except for those who exclusively treat pediatric or obstetric patients, most anesthesiologists are geriatric anesthesiologists at least some of the time. Therefore understanding the numerous physiologic changes of aging is critical for caring for the elderly population. Here we discuss these changes by organ system.
Cardiovascular System
In the cardiovascular system, normal aging manifests as changes in vascular and sympathetic tone, the myocardium, the cardiac conduction system, the cardiac valves, and the baroreceptor system.
Vascular Changes With Age
With age, arterial stiffening results in increased afterload, which increases myocardial oxygen consumption and wall stress. Comorbid pathology such as atherosclerosis and decreased β-2 adrenergic vasodilation may compound this effect.
Partially because of age-related vascular changes, the incidence of venous thromboembolism (VTE) increases exponentially with age, affecting up to 600 people over the age of 80 years per 100,000 annually. All three parts of Virchow’s classic triad (venous stasis, hypercoagulability, and aberrant blood flow) affect older populations and contribute to this increased risk of VTE. For example, venous stasis may result from decreased vascular compliance, a low-flow state such as congestive heart failure, immobility, varicose veins, postmenopausal estrogen replacement therapy, and smoking.
Myocardium
In the absence of pathology, systolic function typically remains well preserved throughout life; however, diastolic dysfunction becomes more common. Age-related myocyte death and reciprocal increases in myocyte size lead to myocardial thickening and decreased elasticity. Chronic hypertension can further exacerbate cardiac hypertrophy. Ventricular thickening and stiffening, in turn, impair early diastolic filling, which falls to 50% of its peak by the age of 80 years. In order to maintain cardiac output, geriatric patients are increasingly dependent on preload and atrial kick. Conversely, small decreases in circulating blood volume can lead to inadequate cardiac filling, which can significantly decrease cardiac output.
Cardiac output is also limited by a lower maximal heart rate relative to younger adults ; maximal heart rate can be estimated as: HR (bpm) = 220 − age (years). In the absence of arrhythmia, aging of the cardiac conduction system and autonomic system leads to decreased heart rate variability and an increased incidence of ectopic beats. Arrhythmia can dramatically decrease cardiac output in older adults. Atrial fibrillation is the most common arrhythmia, affecting 1 in 10 patients 80 years of age or older. Atrial fibrillation eliminates the atrial kick that decreases left ventricular filling and results in decreased cardiac output.
Cardiac Valves
Normal aging results in a thickened and calcified aortic valve. In addition, the pathologic condition of aortic stenosis is more common with aging and is present in 12.4% of those aged 75 years or older. Patients with aortic stenosis depend on good diastolic volume and normal sinus rhythm to maintain myocardial perfusion. Further, patients with aortic stenosis have increased left ventricular diastolic pressure, which means that they are susceptible to decreased coronary perfusion pressure. To avoid myocardial ischemia in patients with aortic stenosis, it is important to avoid hypotension and tachycardia (which reduces the length of diastole and further impairs coronary perfusion). Even minor left ventricular dilation or a relatively small decrease in left ventricular systolic function can increase the likelihood of intraoperative decompensation.
Sympathetic and Autonomic System
The ability of the sympathetic and autonomic systems to respond to physiologic derangement decreases with age. Decreased β-adrenergic sensitivity leads to a lower maximal heart rate, decreased cardiac output, and limited responsiveness to beta agonists (e.g., dobutamine). Baroreceptor impairment increases the incidence of orthostatic hypotension. For this reason, older patients may be more sensitive to prolonged fasting times and may benefit from drinking clear liquids up to 2 hours before surgery.
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