Priorities in Perioperative Geriatrics (2003)

The aging of the baby-boom population and the decreases in adult mortality seen in the last few decades will dramatically increase the age of Americans between 2010 and 2030. During that time, the population older than age 65 yr is expected to grow by 75%, whereas between 1995 and 2050, the cumulative growth of the population older than 85 yr is expected to exceed 400% (1). Furthermore, it has been reported that the increased demand for surgery in this population may exceed the rate of population growth (2). The implications of an aging population for the practice of anesthesiology are profound. Age-related changes in physiology and pharmacology can affect every aspect of perioperative care. The changes in surgical demographics will compel the anesthesiologist to become familiar with the physiology and clinical care of the aged. This review will serve as an introduction. First, some of the physiologic changes that occur with aging will be presented. Second, the preoperative assessment of the older surgical patient will be discussed. Third, some of the research related to intraoperative management of the geriatric surgical patient will be described. In the fourth section, we will discuss some geriatric-specific issues related to postoperative management. Physiologic Changes Relevant to Perioperative Care The most important generalization from physiologic studies of aging is that the basal function of the various organ systems is relatively uncompromised by the aging process per se. However, functional reserve and the ability to compensate for physiologic stress are reduced (Fig. 1).Figure 1: Schematic representation of the relationship between maximal (broken line) and basal (solid line) physiologic function. Functional reserve is the difference between maximal and basal function. Aging inevitably reduces functional reserve even in individuals who are physiologically “young.” The configuration of the curve for basal function is adapted from longitudinal measurements of total (not weight-specific) basal metabolic rate. Reprinted with permission: Muravchick S. Geroanesthesia: principles for management of the elderly patient. St. Louis: Mosby, 1996 (Figures 1–3).Cardiovascular Changes Cardiovascular changes with aging have implications for anesthetic care. Changes in the vascular system and hemodynamics can affect every organ bed. The Framingham Heart Study documented a nearly linear increase in systolic blood pressure from age 30 to 84 yr (3). Age-related hypertension is attributable to a 50%–75% increase in arterial stiffness and a 25% increase in systemic vascular resistance (3,4). Increased sympathetic nervous system activity and decreased peripheral β-adrenergic responsiveness further contribute to the hypertension of aging (5). Ventricular hypertrophy develops in response to increased afterload, increasing wall stress, myocardial oxygen demand, and increasing susceptibility to ischemia. Although intrinsic contractility and resting cardiac output are unaltered with aging, ventricular hypertrophy and stiffening limit the ability of the heart to adjust stroke volume (6) and impair passive ventricular filling. In the elderly, changes in ventricular end-diastolic volume in response to either positive or negative changes in central venous pressure are typically half those seen in young or middle-aged subjects (7). At the same time, fatty infiltration and fibrosis of the heart increases the incidence of sinus, atrioventricular, and ventricular conduction defects (8). With aging there is also decreased myocardial responsiveness to catecholamines and a diminished heart rate response (6). These processes compromise the heart’s ability to buffer changes in circulatory volume, resulting in a disposition to either congestive heart failure or hypotension. From the standpoint of perioperative hemodynamic stability, age-related changes in the autonomic control of heart rate, cardiac output, peripheral vascular resistance, and the baroreceptor response (7,9,10) are as important as the changes in the myocardium and vasculature. Age-related changes in the cardiovascular system involve alterations in both mechanics and control mechanisms; the same can be said of the pulmonary system. Pulmonary System Age-related changes in the pulmonary system parallel changes in the heart. With time, the thorax becomes stiffer, increasing the work of breathing and reducing maximal minute ventilation (11,12). Loss of thoracic skeletal muscle mass aggravates this process. Residual volume and functional residual capacity (FRC) both increase with age—5%–10% and 1%–3% per decade, respectively—whereas the forced expiratory volume in 1 s is reduced approximately 6% to 8% per decade (Fig. 2) (11,13). Because of reduced elastic recoil, the closing volume increases such that it exceeds FRC by age 65 (14). In the supine position, closing capacity may reach FRC by 44 yr of age (11). Inspiratory and expiratory functional reserve decrease with aging, and the normal matching of ventilation and perfusion decreases (15). The respiratory response to hypoxia also diminishes with aging (16); there is a decrease in ciliary function, and cough is reduced (11). Finally, pharyngeal sensation and the motor function required for swallowing are diminished in the elderly (17,18).Figure 2: Mean forced expiratory volume in 1 s (FEV1) versus age for men of differing ethnic groups. Reprinted with permission: Am J Respir Crit Care Med 1999;159:179–87 (Figure 1).Neurologic Changes with Aging Cardiopulmonary complications account for most morbidity and mortality in older surgical patients; however, neurologic morbidity affects a large number of patients, and age-related degenerative changes in the central and peripheral nervous systems contribute to a variety of other morbidities. Both the central and peripheral nervous systems are affected by aging (19). There is a decrease in cortical gray matter through middle age, resulting in cerebral atrophy (20). The ratio of gray to white matter decreases from 1.28 at 20 yr to a low of 1.13 at 50 yr, followed by an increase of this ratio to 1.55 at 100 yr of age. The latter increase appears to reflect a disproportionate loss of white matter in the latest decades (20). For the cortical gray matter, a decrease in neuronal volume appears more important than neuronal loss (21,22). There is also a reduction in the complexity of neuronal connections, a decrease in the synthesis of neurotransmitters, and an increase in the enzymes responsible for their postsynaptic degradation (20). Although cerebral metabolism, blood flow, and autoregulation generally remain intact (20), dendritic regression and the deficiency of neurotransmitters limit the ability of the older brain to integrate multiple neural inputs. Neuronal loss and demyelinization also occur in the spinal cord (23). Functionally, there are changes in spinal cord reflexes and reductions in proprioception. There are also important decreases in hypoxic and hypercarbic drive (11,24). Declines in visual and auditory function further complicate the ability of the nervous system to acquire and process information. This combination of changes can limit the ability of the older patient to understand and process information in the perioperative period. These changes are probably important contributors to postoperative delirium, drug toxicity, and falls. Aging is also associated with neuronal loss in the autonomic nervous system. Sympathetic and parasympathetic ganglia lose neurons, and there is fibrosis of peripheral sympathetic neurons. This peripheral neuronal adrenergic loss is associated with impairment of cardiovascular reflexes. At the same time, decreases in adrenoceptor responsiveness result in increased adrenomedullary output and plasma catecholamine concentrations (9,10,23). Circulating norepinephrine levels have been reported to increase approximately 60% (230 to 380 pg/mL) between age 20 and age 70 (10). Skeletal muscle innervation decreases, translating into a loss of motor units and a decrease in strength, coordination, and fine motor control (25). Joint position and vibration sense may be compromised, and the literature suggests some diminution in the processing of painful stimuli (26,27). However, this effect, if it exists, appears to be modest at best and does not affect all nerve types equally (27–29). Furthermore, given huge interpatient variability in nervous system function and in the experience of pain, alterations in subtypes of pain perception do not translate into a decreased need for analgesia in the elderly (29–32). Renal Aging is accompanied by a progressive decrease in renal blood flow (approximately 10% per decade after age 50) and loss of renal parenchyma (33). Furthermore, by the eighth decade, 10%–30% of remaining nephrons are sclerotic, reducing the functional capacity of the reduced nephronal number (34). Together processes result in a progressive decrease in and rate. However, of loss of muscle aging is not associated with an increase in This and aspect of has implications in the perioperative period. 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