Chapter 14 Surgery in the Geriatric Patient

Alan Dardik, David H. Berger, Ronnie A. Rosenthal

Over the past several generations, life expectancy in the United States has increased significantly. This is primarily the result of the implementation of public health and medical interventions such as improved sanitation, vaccinations, nutrition and lifestyle modifications, and antibiotics. From 1900 to the present, life expectancy at birth has increased almost 30 years (49.2 to 77.8 years), and the average 65-year-woman today can expect to live almost twice as long as her counterpart in 1900, or almost 20 years more (Table 14-1).¹

Table 14-1 Life Expectancy of Older Persons

With this increase in life expectancy comes an increase in the number of people living into old age with diseases and chronic conditions that would have caused death in earlier years. At present, more than 75% of those older than 65 years have at least one chronic condition and 20% of the Medicare population have 5 or more.² Many of these diseases and chronic conditions, such as cancer, degenerative joint disease, coronary artery disease, and visual impairment, have a surgical option as part of the treatment algorithm.

Over the next few decades, as the 78 million people in the Baby Boomer generation (born from 1946 to 1964) begin to reach age 65, there will be a rapid aging of the U.S. population (Fig. 14-1).³ It is expected that by 2030, one in five people will be older than 65 years and, by 2050, almost 20 million people will be older than 85 years. Currently, Social Security, Medicare, and Medicaid benefits to older adults account for more than one third of U.S. spending and have the potential to consume the entire federal budget in the near future. Over the next decade, Medicare costs alone are expected to increase by 7%/year (Fig. 14-2).⁴ The demand for health care services is likely to overwhelm the system if new ways to increase supply and delivery are not developed.

FIGURE 14-1 Aging of the Baby Boom generation and offspring.

(From Purves WK, Orians GH, Heller HC: Life: The science of biology, ed 4, New York, 1994, WH Freeman.)

FIGURE 14-2 Expected growth in Medicare spending over the next decade.

(From Medicare Payment Advisory Commission: A data book: Healthcare spending and the Medicare program, MedPAC, 2009, Washington DC.)

In April 2008, in response to the impending crisis in providing health services to older citizens, the Institute of Medicine (IOM) issued a report, in which the IOM “charged the Committee on the Future Health Care Workforce for Older Americans with determining the health care needs of Americans over 65 years of age and analyzing the forces that shape the health care workforce for these individuals.”² The committee determined that to meet these needs, a three-pronged approach was necessary:

1 Enhancing the geriatric competence of the entire health care work force

2 Increasing the recruitment and retention of geriatrics specialists

3 Improving the way health care is delivered

The goal of this chapter is to help enhance the geriatric competence of surgeons and surgical trainees.

Aging and Surgery

As the number of persons reaching old age continues to grow, there will be a concomitant need to provide surgical care to an increasing number of older patients. Over the past 2 decades alone, the percentage of surgeries in which the patient was older than 65 increased from 19% to 35% of all operations. When obstetric procedures are excluded, this portion rises to 43%. The proportion of the surgical workload across age groups in the specialties in non–federally funded hospitals is shown in Table 14-2.⁵

Table 14-2 Distribution of Procedure Types (by Age Group) Performed in Non–Federally Funded Hospitals (%)

This increase in the percentage of operations in which the patient is older than 65 years is not entirely the result of the increase in the number of older patients; it is also a reflection of a greater willingness to offer surgical treatment to them and an increased expectation of older patients to remain active for as long as possible. Over the past several decades, advances in surgical and anesthetic techniques have allowed us to operate with much greater control and safety. Operative mortality in older patients has declined sharply. As a result, the risk associated with surgery has become somewhat less of a concern than the need to provide maximal medical management of disease.

The pattern of surgical management of malignant disease in older adults is an example of the changing views on surgery in this age group. Data from the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) program have indicated a decrease in the gap between the percentage of younger and older patients treated surgically for certain cancers. For early-stage breast, colon, and rectal cancers, in which the chance of surgical cure is high, the percentage of older patients receiving surgical treatment has approached that of younger patients. For localized gastric, pancreatic, lung, and liver cancers, operative percentages still decline sharply with age (Fig. 14-3).⁶ At present, it is still unclear whether this decline is the result of appropriate decision making based on the overall health of the patient and patient treatment preference, or whether it is a reflection of vestigial prejudice and age bias resulting in patients not being referred for cancer surgery.

FIGURE 14-3 Age distribution of patients receiving cancer-directed surgery for local stage disease.

(Adapted from O’Connell JB, Maggard MA, Ko CY: Cancer-directed surgery for localized disease: Decreased use in the elderly. Ann Surg Oncol 11:962–969, 2004.)

However, additional data from the SEER database indicate that even in the oldest patients, those 90 years and older, cancer treatment is worthwhile. After the first year from diagnosis, relative survival, defined as the ratio of observed survival over a specific period to expected survival, is identical for older and younger cancer patients for up to 10 years (Fig. 14-4).⁷ Most of the difference seen in the first year occurs in the first few months, and the only factor that positively influences first-year survival is whether the patient underwent surgical treatment of the cancer or other major surgery. This finding may be the result of selection bias, inasmuch as only the healthiest 90-year-olds may have been offered surgery. However, this serves to emphasize that age alone should not be the sole reason to deny surgical treatment of cancer.

FIGURE 14-4 Cumulative relative survival of cancer patients by age group from the SEER database, 1973-1998. Note that after the first year, survival curves are parallel for even the oldest old.

(Adapted from Saltzstein SL, Behling CA: 5- and 10-year survival in cancer patients aged 90 and older: A study of 37,318 patients from SEER. J Surg Oncol 81:113–116, 2002.)

There is no doubt that increasing age appears to have a negative effect on the outcome of surgery. However, most studies have indicated that chronologic age alone has little effect on outcome. Rather, it is the age-related decline in physiologic reserves and increase in comorbidity that is responsible for this observation. Even a compromised older patient can tolerate a surgical experience well if the procedure is carefully conducted and the postoperative course is uncomplicated. However, if even one complication occurs, mortality increases significantly. In a study of more than 26,000 patients older than 80 years undergoing major noncardiac surgery in Veterans Affairs Hospitals, mortality rose from 3.7% in patients with no complications to 26.1% in patients in whom one or more complication occurred.⁸

It is also most important to remember that the pattern of symptoms and natural history of the surgical disease in older patients may not be identical to that seen in their younger counterparts. The absence of typical signs and symptoms often leads to errors in diagnosis and delays in treatment. As a result, it is not unusual for an acute complication to be the first indication of disease. For example, acute cholecystitis and common bile duct (CBD) stones are more common indications for cholecystectomy in patients older than 65 years and biliary colic is more common in those younger than 65 years. This is unfortunate, because emergency surgery carries a 3- to 10-fold higher risk of operative mortality than comparable elective surgery. In addition, the extent of disease found at the time of surgery is often far more advanced in older patients when compared with younger patients; over 50% of appendices are perforated at the time of appendectomy in patients older than 65 years compared with less than 25% in those younger than 65 years. Therefore, a high index of suspicion is necessary to identify surgical disease early in older patients presenting with vague complaints or unexplained changes in mental status.

Setting Goals for Treatment

Traditionally, surgeons have measured surgical success in terms of 30-day mortality and morbidity. For older patients, however, the definition of success is more complex. Although we are now able to perform even the most major surgery on our oldest patients with traditional surgical success, the quality of the outcome in the patient’s view is more likely to depend on whether he or she can continue to function as before surgery. For some older patients, losing functional independence as a result of a major surgical intervention may be a far worse outcome than living with, or even dying of, the disease for which surgery is offered.

In a study of older patients with limited life expectancy because of serious chronic disease, Fried and colleagues ⁹ examined the impact of treatment burden (low, minor interventions, such as IV antibiotics; high, major interventions, such as surgery) and expected outcome (desirable versus undesirable) on patient preferences for treatment. Results indicated that more than 70% of older patients would not want even a low burden treatment if severe functional impairment or cognitive impairment was the expected outcome. The concern for functional and cognitive impairment was more dramatic than the concern for death (Fig. 14-5).

FIGURE 14-5 Many patients are willing to undertake high- or low-burden treatments, even if the risk of death is high (up to 50%). However, when there is even a small risk of cognitive or functional decline, the number of patients willing to undergo even a low-burden treatment sharply declines.

(Adapted from Fried TR, Bradley EH, Towle VR, et al: Understanding the treatment preferences of seriously ill patients. N Engl J Med 346:1061–1066, 2002.)

In another study of preferences for permanent nursing home placement in seriously ill hospitalized patients, 56% of patients were very unwilling or would rather die than live permanently in a nursing home. Correlation between the patient’s wishes and both the surrogate’s and physician’s opinion of the patient’s wishes was poor.¹⁰

Therefore, it is essential that the older patient be given a realistic estimate of the overall functional outcome of the proposed surgical treatment, in addition to the likelihood of control or cure of the particular disease. It is also essential that the surgeon understands the patient’s preferences in the context of this broader view of surgical success.

Physiologic Decline

With aging, there is a decline in physiologic function in all organ systems, but the magnitude of this decline is variable among organs and individuals. In the resting state, this decline usually has minimal functional consequence, although physiologic reserves may be used just to maintain homeostasis. However, when physiologic reserves are required to meet the additional challenges of surgery or acute illness, overall performance may deteriorate. This progressive age-related decline in organ system homeostatic reserves, termed homeostenosis, was first described by the physiologist Walter Cannon in the 1940s. Figure 14-6 is a graphic representation of the present concepts of homeostenosis.¹¹ With older age, there is increased use of physiologic reserves just to maintain normal homeostasis. Therefore, when stressed, fewer reserves are available to meet the challenge, and overall function may be pushed over the precipice of organ failure or death.

FIGURE 14-6 Graphic representation of homeostenosis. With advancing age, physiologic reserves are increasingly used to maintain homeostasis. Vertical arrows represent challenges such as surgical stress or acute illness. Because reserves are already used, there are fewer available to meet these challenges. As a result, the precipice is crossed by a stress that would be easily tolerated in younger age. This precipice may be any relevant clinical marker, such as organ dysfunction or failure or death.

(Adapted from Taffett GE: Physiology of aging. In Cassel CK, Leipzig RM, Cohen HJ, et al. [eds]: Geriatric medicine: An evidence-based approach, ed 4, New York, 2003, Springer-Verlag, pp 27–35.)

Over the past several decades, an enormous amount of research has been conducted to define the specific changes in organ function that are directly attributable to aging. This task is inherently difficult because aging is also accompanied by increased vulnerability to disease. It is often difficult to determine whether an observed decline in function is secondary to aging per se or to disease associated with aging. The overall effect, however, is still the same—a much smaller margin for error in the care of older patients. Understanding the changes in organ function can help minimize these errors.

Cardiovascular System

Cardiovascular disease is the leading cause of death in the United States in men and women. Of these deaths, 83% occur in persons older than 65 years (Box 14-1). The prevalence of heart failure approaches 10 in 1000 persons in this age group. Congestive heart failure is a risk factor for several postoperative complications, including surgical site infections. Cardiac events are common in the postoperative period in older patients and are attributable to disease and to changes in the structure and function of the heart that accompany aging.

Morphologic changes are found in the myocardium, conducting pathways, valves, and vasculature of the heart and great vessels with increasing age. The number of myocytes declines as the collagen and elastin content increases, thereby resulting in fibrotic areas throughout the myocardium and an overall decline in ventricular compliance. Almost 90% of the autonomic tissue in the sinus node is replaced by fat and connective tissue, and fibrosis interferes with conduction in the intranodal tracts and bundle of His. These changes contribute to the high incidence of sick sinus syndrome, atrial arrhythmia, and bundle branch block. Sclerosis and calcification of the aortic valve are common but are usually of no functional significance. Progressive dilation of all four valvular annuli is probably responsible for the multivalvular regurgitation demonstrated in healthy older persons. Finally, there is a progressive increase in rigidity and decrease in distensibility of the coronary arteries and great vessels. Changes in the peripheral vasculature contribute to increased systolic blood pressure, increased resistance to ventricular emptying, and compensatory loss of myocytes, with ventricular hypertrophy.

The direct functional implications of these changes are difficult to assess accurately because age-related changes in body composition, metabolic rate, general state of fitness, and underlying disease all influence cardiac performance. It is now generally accepted that systolic function is well preserved with increasing age. Cardiac output and ejection fraction are maintained, despite the increase in afterload imposed by stiffening of the outflow tract. The mechanism whereby cardiac output is maintained during exercise, however, is somewhat different. In younger persons, output is maintained by increasing the heart rate in response to β-adrenergic stimulation. With aging, there is a relative hyposympathetic state in which the heart becomes less responsive to catecholamines, possible secondary to declining receptor function. The aging heart therefore maintains cardiac output not by increasing its rate, but by increasing ventricular filling (preload). Because of the dependence on preload, even minor hypovolemia can result in significant compromise in cardiac function.

Diastolic function, however, which depends on relaxation rather than contraction, is affected by aging.¹² Diastolic dysfunction is responsible for up to 50% of cases of heart failure in patients older than 80 years. Myocardial relaxation is more energy-dependent and therefore requires more oxygen than contraction. With aging, there is a progressive decrease in the partial pressure of oxygen. Consequently, even mild hypoxemia can result in prolonged relaxation, higher diastolic pressure, and pulmonary congestion. Because early diastolic filling is impaired, maintenance of preload becomes even more reliant on atrial kick. Loss of the atrial contribution to preload can result in further impairment of cardiac function.

It is also important to remember that the manifestation of cardiac disease in older adults may be nonspecific and atypical. Although chest pain is still the most common symptom of myocardial infarction, atypical symptoms such as shortness of breath, syncope, acute confusion, or stroke will occur in as many as 40% of older patients.

Respiratory System

Chronic lower respiratory disease is the fourth leading cause of death after heart disease, cancer, and stroke. Respiratory problems are the most common postoperative complications in older patients (Box 14-2). Both disease- and age-related changes in lung structure and function contribute to this vulnerability.¹³

With aging there is a decline in respiratory function that is attributable to changes in the chest wall and lungs. Chest wall compliance decreases secondary to changes in structure caused by kyphosis and is exaggerated by vertebral collapse. Calcification of the costal cartilage and contractures of the intercostal muscles result in a decline in rib mobility. Maximum inspiratory and expiratory forces decrease by as much as 50% as a result of a progressive decrease in the strength of the respiratory muscles.

In the lung, there is loss of elasticity, which leads to increased alveolar compliance with collapse of the small airways and subsequent uneven alveolar ventilation with air trapping. Uneven alveolar ventilation leads to ventilation-perfusion mismatches, which in turn causes a decline in arterial oxygen tension of approximately 0.3 or 0.4 mm Hg/ year. The partial pressure of CO₂ does not change, despite an increase in dead space. This may be caused, in part, by the decline in production of CO₂ that accompanies the falling basal metabolic rates. Air trapping is also responsible for an increase in residual volume, or the volume remaining after maximal expiration.

Loss of support of the small airways also leads to collapse during forced expiration, which limits dynamic lung volumes and flow rates. Forced vital capacity decreases by 14 to 30 mL/year and forced expiratory volume in 1 second (FEV₁) decreases by 23 to 32 mL/year (in males). The overall effect of loss of elastic inward recoil of the lung is balanced somewhat by the decline in chest wall outward force. Total lung capacity therefore remains unchanged, and there is only a mild increase in resting lung volume, or functional residual capacity. Because total lung capacity remains unchanged, the increase in residual volume results in a decrease in vital capacity.

Control of ventilation is also affected by aging. Ventilatory responses to hypoxia and hypercapnia fall by 50% and 40%, respectively. The exact mechanism of this decline has not been well defined but it may be caused by declining chemoreceptor function at the peripheral or central nervous system level.

In addition to these intrinsic changes, pulmonary function is affected by alterations in the ability of the respiratory system to protect against environmental injury and infection. There is a progressive decrease in T cell function (see later), decline in mucociliary clearance, and decrease in several components of swallowing function. Loss of the cough reflex secondary to neurologic disorders, combined with swallowing dysfunction, may predispose to aspiration. The increased frequency and severity of pneumonia in older persons have been attributed to these factors and to an increased incidence of oropharyngeal colonization with gram-negative organisms. This colonization correlates closely with comorbidity and with the ability of older patients to perform activities of daily living (ADLs). This fact lends support to the idea that functional capacity is a crucial factor in assessing the risk for pneumonia in older patients.

Renal System

Approximately 25% of all Americans 70 years and older have moderately or severely decreased kidney function (Box 14-3). Between the ages of 25 and 85, there is a progressive decrease in the renal cortex. Over time, approximately 40% of the nephrons become sclerotic. The remaining functional units hypertrophy in a compensatory manner. Sclerosis of the glomeruli is accompanied by atrophy of the afferent and efferent arterioles and by a decrease in renal tubular cell number. Renal blood flow also falls by approximately 50%. Functionally, there is a decline in the glomerular filtration rate (GFR) of approximately 45% by age 80 years.

Renal tubular function also declines with advancing age. The ability to conserve sodium and excrete hydrogen ion decreases, resulting in a diminished capacity to regulate fluid and acid-base balance. Dehydration becomes a particular problem because losses of sodium and water from nonrenal causes are not compensated for by the usual mechanisms. The inability to retain sodium is believed to be caused by a decline in the activity of the renin-angiotensin system. The increasing inability to concentrate the urine is related to a decline in end-organ responsiveness to antidiuretic hormone. The marked decline in the subjective feeling of thirst is also well documented but not well understood. Alterations of osmoreceptor function in the hypothalamus may be responsible for the failure to recognize thirst in spite of significant elevations in serum osmolality.¹⁴

Because of the decline in renal function with aging, it is often important to measure GFR in older patients as part of preoperative risk assessment and in hospital to provide accurate medication dosing. In older hospital patients, direct measurement of creatinine clearance (CrCl) is difficult because incontinence and cognitive impairment make 24-hour urine collection unreliable. Serum creatinine level measurement may be an unreliable indicator of renal function status because this value may remain unchanged as a result of a concomitant decrease in lean body mass and thus a decrease in creatinine production. A serum creatinine level of 1.0 mg/dL may represent a CrCl of over 100 mL/min in a 30-year old, but less than 60 mL/min in an 85-year old.¹⁵

To overcome these problems, formulas have been developed to estimate CrCl from plasma creatinine and patient characteristics. The most commonly used formulas are the Cockcroft-Gault equation and the Modification of Diet in Renal Disease (MDRD) equation (Fig. 14-7). In a large study of older hospitalized patients, the Cockcroft-Gault equation has been shown to correlate more closely with directly measured CrCl.¹⁶

FIGURE 14-7 Equations for calculating creatinine clearance.

Acute kidney injury (AKI) is defined as a 0.3-mg/dL or 50% or higher change in the serum creatinine level from baseline or a reduction in urine output of less than 0.5 mL/kg/hr over a 6-hour interval, within a 48-hour period, following adequate volume resuscitation. AKI is a frequent occurrence after major surgery. Up to 7.5% of patients with a normal preoperative serum creatinine level will develop AKI. AKI is associated with increased short-term morbidity and mortality, as well as increased long-term mortality. Age, in addition, to emergency surgery, ischemic heart disease, and congestive heart failure, are risk factors for the development of postoperative AKI. Furthermore, older patients with already compromised renal function are at increased risk of postoperative AKI. The keys to avoiding postoperative AKI is to understand that older patients are at increased risk and to take steps to avoid unnecessary hypovolemia and ensure proper dosing of drugs that are cleared by the kidney and of drugs that are nephrotoxic.

The lower urinary tract also changes with increasing age. In the bladder, increased collagen content leads to limited distensibility and impaired emptying. Overactivity of the detrusor muscle secondary to neurologic disorders or idiopathic causes has also been identified. In women, decreased circulating levels of estrogen and decreased tissue responsiveness to this hormone cause changes in the urethral sphincter that predispose to urinary incontinence. In men, prostatic hypertrophy impairs bladder emptying. Together, these factors lead to urinary incontinence in 10% to 15% of older persons living in the community and 50% of those in nursing homes. There is also an increased prevalence of asymptomatic bacteruria with age, which varies from 10% to 50% depending on gender, level of activity, underlying disorders, and place of residence. Urinary tract infections alone are responsible for 30% to 50% of all cases of bacteremia in older patients. Alterations in the local environment and declining host defenses are thought to be responsible. Because of the lack of symptoms in older patients with bacteruria, preoperative urinalysis is important.

Hepatobiliary System

Overall, hepatic function is well preserved with aging. However, there is as much as a fourfold increase in liver disease–related mortality in persons between the ages of 45 and 85 years.¹⁷ Morphologic changes include a decrease in the number of hepatocytes and a reduction in overall weight, size, and volume. There is, however, a compensatory increase in cell size and proliferation of bile ducts. Functionally, hepatic blood flow decreases by approximately 0.3% to 1.5%/year to 40% to 45% of earlier values after 65 years of age.

The synthetic capacity of the liver, as measured by standard tests of liver function, remains unchanged (Box 14-4). However, the metabolism of and sensitivity to certain types of drugs is altered. Drugs requiring microsomal oxidation (phase I reactions) before conjugation (phase II reactions) may be metabolized more slowly, whereas those requiring only conjugation may be cleared at a normal rate. Drugs that act directly on hepatocytes, such as warfarin (Coumadin), may produce the desired therapeutic effects at lower doses in older adults because of an increased sensitivity of cells to these agents. Some recent evidence has also suggested that aging may be associated with a decline in the ability of the liver to protect against the effects of oxidative stress.

Box 14-4 Major Hepatobiliary Changes With Age

Decrease in the number of hepatocytes

Decline in hepatic blood flow

Synthetic capacity remains unchanged

Increased sensitivity to and decreased clearance of certain drugs

Increased incidence of gallstones and gallstones related diseases

The most significant correlate of altered hepatobiliary function in older adults is the increased incidence of gallstones and gallstone-related complications. Gallstone prevalence rises steadily with age, although there is variability in the absolute percentages, depending on the population. Stones have been demonstrated in as many as 80% of nursing home residents older than 90 years. Biliary tract disease is the single most common indication for abdominal surgery in older adults (see later).

Immune Function

Immune competence, like other physiologic parameters, declines with advancing age (Box 14-5). This immunosenescence is characterized by enhanced susceptibility to infections, an increase in autoantibodies and monoclonal immunoglobulins, and an increase in tumorigenesis. In addition, like other physiologic systems, this decline may not be apparent in the unchallenged state. For example, there is no decline in neutrophil count with age, but the ability of the bone marrow to increase neutrophil production in response to infection may be impaired. Older patients with major infections frequently have normal white blood cell (WBC) counts, but the differential count will show a profound shift to the left, with a large proportion of immature forms.

Box 14-5 Major Changes in Immune Function With Age

Decrease production and differentiation of naïve T cells

Decrease in T cell mitogenic activity

Increase in inflammatory cytokines

Increased autoantibodies

With aging, there is a decline in the hematopoietic stem cell pool in the bone marrow that leads to decreased production of naïve T cells from the thymus and of B cells from the bone marrow. Moreover, involution of the thymus gland, with a decline in thymic hormone levels, further impairs the production and differentiation of naïve T cells and leads to an increased proportion of memory T cells. This change in the population of T cells leaves older adult hosts less able to respond to new antigens. Furthermore, recent data have suggested that chronic infection with viruses such as cytomegalovirus produces nonfunctional T cell clonal expansions that may limit the space available for proliferating T cells.¹⁸

Some B cell defects have recently been identified, although it is thought that the functional deficits in antibody production are related to altered T cell regulation rather than intrinsic B cell changes. In vitro, there is increased helper T cell activity for nonspecific antibody production, as well as a decreased ability of suppressor T cells from old mice to recognize and suppress specific antigens from self. This is reflected in an increase in the prevalence of autoantibodies to more than 10% by 80 years of age. The mix of immunoglobulins also changes; immunoglobulin M (IgM) levels decrease, whereas IgG and IgA levels increase slightly.

Changes in the immune system with aging are similar those seen in chronic inflammation and cancer. In addition to the reduced mitogenic responses of T cells, there is an increase in the levels of acute-phase proteins. It is hypothesized that persistently elevated levels of inflammatory cytokines may be responsible for the downregulation of interleukin-2 production by chronically stimulated T cells. Markers of inflammation such as interleukin-6 have recently been shown to be increased in older patients. Chronic inflammation has been implicated in the syndrome of frailty, which is characterized by loss of muscle mass (sarcopenia), undernutrition, and impaired mobility. Inflammatory cytokines are also implicated in the normocytic anemia that is common in frail older adults.

The clinical implications of these changes are difficult to determine. When superimposed on the known immunosuppression caused by the physical and psychological stresses of surgery, insufficient immunologic responses are to be expected in older adults. The increased susceptibility to many infectious agents in the postoperative period, however, is more likely the result of a combination of stress and comorbid disease rather than physiologic decline alone.

Glucose Homeostasis

Data from the National Health and Nutrition Examination Survey have shown a clear increase in the prevalence of disorders of glucose homeostasis with age; more than 20% of persons older than 60 years have type 2 diabetes. An additional 20% have glucose intolerance characterized by normal fasting glucose and a postchallenge glucose level higher than 140 mg/dL but less than 200 mg/dL. This glucose intolerance may be the result of a decrease in insulin secretion, increase in insulin resistance, or both (Fig. 14-8).¹⁹

FIGURE 14-8 The normal response to hyperglycemia is for the beta cell to adapt and secrete sufficient insulin to restore euglycemia. In aging, there is a decrease in insulin secretion and a probable increase in insulin resistance, which, when combined with comorbid illness, genetic factors, and medications, leads to a failure of this glucoregulatory process. IGT, Impaired glucose tolerance.

(From Chang AM, Halter JB: Aging and insulin secretion. Am J Physiol Endocrinol Metab 284:E7–E12, 2003.)

There is now general consensus that beta cell function declines with age. This change is manifested by failure of the beta cell to adapt to the hyperglycemic milieu with an appropriate increase in insulin response. The question of insulin resistance is more controversial. Although insulin action has been shown to decrease in older adults, this change is thought to be more a function of changing body composition, with increased adipose tissue and decreased lean body mass, rather than age per se. Others believe that there is an increase in insulin resistance directly attributable to aging, as manifested by a decrease in insulin-mediated glucose uptake in muscle that is normally regulated by the glucose transporter GLUT-4. There is also an increase in intracellular lipid accumulation, which interferes with normal insulin signaling. These changes may be associated with the decline in mitochondrial function that also accompanies aging.¹⁹

These factors, combined with comorbid illness, medications, and genetic predisposition, come together to render older surgical patients at particularly high risk for uncontrolled hyperglycemia when subjected to the usual insulin resistance that accompanies the physiologic stress of surgery. Both the endogenous glucose response to traumatic stress and glycemic response to an exogenous glucose load are exaggerated in injured older patients.

Although most of the data on glucose control and surgical outcomes is in the cardiac surgery literature, recent evidence has confirmed that uncontrolled hyperglycemia in the immediate perioperative period is associated with an increase in infections in almost all types of surgery. The optimum level of glucose control, however, is still controversial. Earlier prospective studies indicated that tight control of blood sugar (80 to 110 mg/dL) achieved by continuous infusion of insulin improved some outcomes, including mortality in critically ill patients in the surgical intensive care unit, but more recent data have cast some doubt on the benefits of such strict control. In general, maintenance of the blood glucose level below 180 mg/dL in the perioperative period is now widely accepted as an appropriate target, even in older patients.

Preoperative Assessment

The goals of preoperative assessment of an older patient are to define the extent of physiologic decline, characterize and optimize comorbid diseases, and determine how the stress of the surgical treatment will affect the patient’s postoperative function and overall quality of life. Extensive testing for disease in every organ system is neither cost-effective, practical, nor necessary for most patients. A thorough history and physical examination will provide information to direct further workup, if necessary. It is important, however, to adjust the history and physical examination to look carefully for the risk factors, signs, and symptoms of the more common comorbid conditions. The addition of simple tools for the assessment of functional, cognitive, nutritional status and overall frailty will significantly enhance understanding of the individual patient’s true operative risk (Box 14-6). When initial evaluation identifies specific disease or risk factors for disease, further workup may be indicated.

Comorbidity

Like the surgical disease itself, the manifestations of comorbid illnesses in older adults are frequently less typical than in younger patients. For example, more than 40% of myocardial infarctions in patients older than 75 to 84 years are silent or unrecognized, as opposed to less than 20% in patients between the ages of 45 and 54. Cognitive and nutritional deficits occur frequently in the aged, but as many as two thirds and one half, respectively, are overlooked unless a specific assessment is undertaken. Swallowing disorders are also common but are often unrecognized.

In addition, comorbidity influences the overall life expectancy of the individual, irrespective of the surgical illness. For example, the mean life expectancy of cognitively intact persons aged 65 to 69 years is approximately 18 years, whereas the life expectancy for similarly aged patients with dementia is closer to 10 years. In older persons with congestive heart failure, 20% die within 1 year and 75% within 5 years of initial hospitalization. Understanding the impact of comorbidity on life expectancy is therefore essential in risk-benefit determinations.

Of all comorbid conditions, cardiovascular disease is the most prevalent, and cardiovascular events are a leading cause of severe perioperative complications and death. Therefore, the main thrust of preoperative evaluation in most patients, regardless of age, has focused on identifying patients at risk for cardiac complications. The American College of Cardiology (ACC) and American Heart Association (AHA) Task Force on Practice Guidelines first published an in-depth set of guidelines for preoperative cardiac evaluation in 1996, with updates in 2002 and 2007.²⁰ These guidelines provide a stepwise Bayesian strategy for determining which patients will need further testing to clarify risk or further treatment to minimize risk. Stratification is based on factors related to the patient and type of surgery. For older patients with known cardiac disease, rigorous workup may be necessary. For most patients, assessment of exercise tolerance and functional capacity is an accurate method of predicting the adequacy of cardiac and pulmonary reserves (see later).

Although the main focus of preoperative evaluation has been cardiac status, pulmonary complications in older patients are at least as common as cardiac complication, if not more so. Risk factors for pulmonary complications are not as well studied as those for cardiac complications, although many of the same issues apply to both. Poor exercise capacity and poor general health predict pulmonary and cardiac complications. In a systematic review of the literature for risk factor for pulmonary complications after noncardiac surgery (not limited to older adults) both patient and procedural factors were identified (Table 14-3).²¹ Age older than 80 years was associated with the highest odds ratio (OR) of a pulmonary complication, even after adjusting for comorbidity. Indicators of impaired function, nutrition, and cognition, among others, were also important. Aortic aneurysm and thoracic and abdominal operations were the strongest procedure-related factors, but others, such as abdominal surgery, prolonged surgery, and emergency surgery, were also important.

Table 14-3 Potential Risk Factors for Postoperative Pulmonary Complications

Additional comorbid conditions, such as prior stroke, gastroesophageal reflux disease (GERD), and poor dentition, also place older patients at increased risk of aspiration. Subtle changes in cognitive and swallowing function are similarly common in older adults and are associated with aspiration pneumonia and other negative outcomes. Initial screening for aspiration risk can be accomplished easily with a simple 3-ounce water swallow test, which has been shown to have high sensitivity and negative predictive value. This test is accomplished by asking the patient to swallow 90 mL of water without stopping. Choking, coughing, wet quality to the voice after swallowing, or failure to complete the test indicates that a more thorough swallowing examination may be in order. Passing this test indicates a low risk for aspiration; however, the false-positive rate is high. Aspiration precautions, however, should be instituted for all older patients with any risk factors for aspiration

In a recent review of strategies to reduce postoperative pulmonary complications, only lung expansion interventions, such as incentive spirometry, were shown by good evidence to have an effect.²² The selective use of nasogastric decompression (rather than routine use) and short-acting (as opposed to long-acting) intraoperative neuromuscular blockade was supported by fair evidence. Evidence supporting smoking cessation, epidural anesthesia and analgesia, laparoscopic versus open approaches, and nutritional supplementation was insufficient or conflicting.

Function

Postoperative outcome in the geriatric surgical patient is largely determined by the impact of physiologic decline and comorbidity on an individual’s functional reserves. Limited preoperative functional reserves also contribute to postoperative immobility, which in turn leads to complications such as atelectasis and pneumonia, venous stasis and pulmonary embolism, and multisystem deconditioning (see later). Function can be assessed in many ways.

American Society of Anesthesiologists Classification

For decades, the physical status classification of the American Society of Anesthesiologists (ASA) has been used successfully to stratify operative risk. This simple classification ranks patients according to the functional limitations imposed by coexisting disease. When curves for mortality versus ASA class are examined with regard to age, there is little difference between younger and older patients, which indicates that mortality is a function of coexisting disease rather than chronologic age. ASA classification has been shown to predict postoperative mortality accurately, even in patients older than 80 years. In a large multicenter Department of Veterans Affairs study (National Surgical Quality Improvement Program [NSQIP]), surgical patients were assessed prospectively for operative risk and risk-adjusted models were then created to allow comparison of the quality of surgical care among different institutions. Of the 68 variables studied, the ASA functional classification was the factor most predictive of postoperative morbidity and the second most predictive of mortality.²³

Activities of Daily Living

The ability to perform ADLs (e.g., feeding, continence, transferring, toileting, dressing, bathing) and instrumental ADLs (IADLs; e.g., telephone use, transportation, meal preparation, shopping, housework, medication management, managing finances) have also been shown to correlate with postoperative mortality and morbidity.²⁴ Inactivity, defined as the inability to leave the home on one’s own at least twice per week, has been associated with a higher incidence of all major surgical complications. Postoperative mortality in severely limited patients has been reported to be almost 10 times higher than mortality in active patients. In another study of functional recovery after major elective open abdominal operations, better recovery and shorter time to recovery of ADLs and IADLs were almost always predicted by a better preoperative physical performance status, as measured by three simple tests of strength and mobility.²⁵

Exercise Tolerance

Of all the methods of assessing overall functional capacity, exercise tolerance is the most sensitive predictor of postoperative cardiac and pulmonary complications in older adults. In an older but frequently quoted study comparing exercise tolerance and other assessment techniques, Gerson and associates demonstrated that an inability to raise the heart rate to 99 beats/min while performing 2 minutes of supine bicycle exercise was the most sensitive predictor of postoperative cardiac and pulmonary complications and death.²⁶

Formal exercise testing, however, is not necessary in every older patient. The metabolic requirements for many routine activities have already been determined and are quantitated as metabolic equivalents (MET). One MET, defined as 3.5 mL/kg/min, represents the basal oxygen consumption of a 70-kg, 40-year-old man at rest. Estimated energy requirements for various activities are shown in Figure 14-9. An inability to function above 4 METs has been associated with increased perioperative cardiac events and long-term risk. By asking appropriate questions about the level of activity, functional capacity can be accurately determined without the need for additional testing.

FIGURE 14-9 Estimated energy requirements for various activities. With increasing activity, the number of METs increases. An inability to function above 4 METs has been associated with increased perioperative cardiac events and long-term risk.

(From Eagle KA, Berger PB, Calkins H, et al; American College of Cardiology/American Heart Association Task Force on Practice Guidelines [Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery]: ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgery—executive summary. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines [Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery]. Circulation 105:1257–1267, 2002.)