Handbook of Clinical Anesthesia
Anesthesia for the older patient
All caregivers, including anesthesiologists, should be knowledgeable of at least some aspects of aging in order to provide intelligent modification of their standard practice (Rooke GA: Geriatric anesthesia. In Clinical Anesthesia. Edited by Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC. Philadelphia: Lippincott Williams & Wilkins, 2009, pp 876–888).
- Demographics and Economics of Aging
- When Social Security was initiated in 1935, only 6.1% of the U.S. population was older than 65 years old. By 2005, that percentage had more than doubled to 12.4%, and by 2035, it is expected to be more than 20% of the U.S. population.
- Elderly patients account for more than 44% of all inpatient days. Of the 26.6 million inpatient surgical procedures in 2004, 33% were performed on elderly patients.
- It is estimated that people older than age 65 years account for nearly half of the nation's health care costs.
- The Process of Aging
- Mammalian aging clearly involves a gradual, cumulative process of damage and deterioration.
- Protective mechanisms against aging are costly to the organism. The “disposable soma” theory of aging states that anti-aging mechanisms only need to be good enough to give the next generation the best opportunity to reproduce. In fact, most of the gains in average human lifespan have been as the result of reducing the factors that cause premature death (accidents, violence, disease).
- The inability to completely thwart aging implies that the average human lifespan is limited and that if everyone only died of “old age,” the age at death would end up being a bell-shaped curve centered at a certain value, probably around age 85 years.
- A variety of deleterious processes continually attack DNA, proteins, and lipids (free radicals and non-enzymatic glycosylation of sugars and amines).
- Collagen becomes stiffer from aromatic ring cleavage and by cross-linking to other collagen molecules. In the cardiovascular system, arteries, veins, and the myocardium all stiffen with age.
- DNA damage occurs, and mitochondrial DNA suffers more damage than nuclear DNA.
- Caloric restriction, well documented to increase lifespan in small mammals, probably does so by decreasing the rate of oxidative damage.
- Functional Decline and the Concept of Frailty
- Functional reserve represents the degree to which organ function can increase above the level necessary for basal activity. For healthy individuals, reserve peaks at approximately age 30 years, gradually declines over the next several decades, and then experiences more rapid decline beginning around the eighth decade of life. Anesthesiologists often assess the patient's reserve.
- The ability to achieve the desired minimum of four metabolic equivalents (METs) presumably provides enough cardiovascular reserve to tolerate the stress of most surgical procedures.
- Even without formal assessment, an intuitive sense of reserve is often obtained through simple observation (loss of subcutaneous tissue, unsteady or slowed gait, stooped body habitus, minimal muscle mass [sarcopenia]).
- Diminished mentation is a risk factor for postoperative delirium.
- Physiologic Age
- The rate at which a given individual ages is highly variable and is determined to a great extent by genetics and luck at avoiding illnesses, trauma, or environmental exposure that may contribute to functional loss. Nevertheless, successful aging can be promoted through avoidance of obesity, good nutrition, and regular exercise.
- The older we get, the less likely our chronologic age reflects our physiologic status and functional reserve.
III. The Physiology of Organ Aging
- Changes in Body Composition and Liver and Kidney Aging
- Changes in body composition are primarily characterized by a gradual loss of skeletal muscle and an increase in body fat, although the latter is more prominent in women.
- Basal metabolism declines with age, with most of the decline accounted for by the change in body composition. A reduction in total body water reflects the reduction in cellular water that is associated with a loss of muscle and an increase in adipose tissue.
- Aging causes a small decrease in plasma albumin levels and a small increase in α1-acid glycoprotein, yet the effect of these changes on drug protein binding and drug delivery appears to be minimal.
- Liver mass decreases with age and accounts for most, but not all, of the 20% to 40% decrease in liver blood flow. Even in very old individuals, liver reserve should be more than adequate.
- Renal cortical mass also decreases by 20% to 25% with age, but the most prominent effect of aging is the loss of up to half of the glomeruli by age 80 years.
- The decrease in the glomerular filtration rate (GFR) after age 40 years typically reduces renal excretion of drugs to a level so that drug dosage adjustment becomes a progressively important consideration beginning at approximately age 60 years. Nevertheless, the degree of decline in GFR is highly variable and is likely to be much less than predicted in many individuals.
- Aged kidneys do not eliminate excess sodium or retain sodium when necessary as effectively as kidneys in young adults. Fluid and electrolyte homeostasis is more vulnerable in older patients, particularly when the patient has acute injury or disease and eating and drinking becomes more of a chore.
- Aging is associated with decreased insulin secretion in response to a glucose load. It is also associated with increased insulin resistance, particularly in skeletal
muscle (even healthy elderly patients may require insulin therapy more often perioperatively than young adults).
- Central Nervous System Aging
- Brain mass begins to decrease slowly starting at approximately age 50 years and declines more rapidly later such that an 80-year-old brain has typically lost 10% of its weight.
- Neurotransmitter functions suffer more significantly, including dopamine, serotonin, γ-aminobutyric acid (GABA) and especially the acetylcholine system (which is connected to Alzheimer's disease). Nearly half of patients age 85 years and older demonstrate significant cognitive impairment.
- Some degree of atherosclerosis appears to be inevitable.
- Contrary to prior belief, the aged brain does make new neurons and is capable of forming new dendritic connections.
- There is an approximate 6% decrease in the minimum alveolar concentration (MAC) per decade after age 40 years. For many intravenous (IV) anesthetic agents, the same brain concentration produces approximately twice the effect in an older person than a young adult.
- Age is a major risk factor for postoperative delirium and cognitive decline.
- Drug Pharmacology and Aging (Table 35-1)
- Drugs often have more pronounced effects in older patients. The cause can be either pharmacodynamic, in which case the target organ (often the brain) is more sensitive to a given drug tissue level, or pharmacokinetic, in which case a given dose of drug commonly produces higher blood levels in older patients.
- Typically, the initial blood concentration of bolus drugs is higher in older patients, partly because of a mildly contracted blood volume. Despite the typically enhanced effect of bolus drugs on older patients, there is a general impression that bolus drugs take longer to achieve that greater effect (the reasons are unclear).
- The most prominent pharmacokinetic effect of aging is a decrease in drug metabolism because of both a decrease in clearance and an increase in Vdss(increase in body fat). In addition, elderly patients often take a host of
chronic medications, a setup for drug interactions as well as for inhibition of drug metabolism.
Table 35-1 Effect of Age on Drug Dosing
Table 35-2 The Effects of Aging on the Cardiovascular System
- Drugs with primarily renal elimination experience decreased metabolism because of reductions in GFR with aging. The net effect on drug metabolism is typically a doubling of the elimination half-life between old and young adults. In the case of diazepam, the half-life in hours is roughly equal to the patient's age.
- The concept of the context-sensitive half-time (time necessary for a 50% [or any desired percent] decrease in plasma concentration after termination of an infusion) is often increased in elderly patients.
- Cardiovascular Aging
- Pulmonary Aging
- The most prominent effects of aging on the pulmonary system are stiffening of the chest wall and a decrease in elasticity of the lung parenchyma.
- The need for greater lung inflation to prevent small airway collapse is reflected by the increase in closing capacity with age. Closing capacity typically exceeds functional residual capacity in the mid 60s and eventually exceeds the tidal volume at some later age.
- These changes, plus a modest reduction in alveolar surface area with age, contribute to a modest decline in resting PaO2.
- Changes within the nervous system further influence the respiratory system. Aging leads to an approximate 50% decrease in the ventilatory response to hypercapnia and an even greater decrease in the response to hypoxia, especially at night.
- Generalized loss of muscle tone with age applies to the hypopharyngeal and genioglossal muscles and predisposes elderly individuals to upper airway obstruction.
- A high percentage, perhaps even 75%, of people older than age 65 years have sleep-disordered breathing, a phenomenon that may or may not be the same as sleep apnea, but certainly places elderly individuals at increased risk for postoperative hypoxia.
- Aging also results in less effective coughing and impaired swallowing. Aspiration is a significant cause of community-acquired pneumonia and may well play a role in the development of postoperative pneumonia.
VII. Thermoregulation and Aging
- Elderly individuals are prone to hypothermia when stressed by modestly cold environments that would not affect younger individuals.
- Aging has a variable effect on vasoconstriction and shivering, with some elderly people demonstrating responses identical to young subjects and others demonstrating a near-absent response. Overall vasoconstriction and metabolic heat production are diminished in magnitude in elderly individuals.
- The increased risk of intraoperative hypothermia in elderly patients owing to effective vasoconstriction is compounded by decreased basal metabolism (heat production) in elderly patients. (Hypothermia has been observed more frequently in older patients than in their younger counterparts.)
- The risks of hypothermia include myocardial ischemia, surgical wound infection, coagulopathy with increased blood loss, and impaired drug metabolism.
VIII. Conduct of Anesthesia
- The Preoperative Visit
- The preoperative visit should begin with a detailed review of the patient's medical history, current
functional status of all vital organs, and medication list. Basic laboratory testing is not warranted for older subjects. Some additional issues more prevalent among elderly patients should also be raised. For example, whether the patient's living situation is capable of providing the support necessary for a successful recovery should be explored.
- Elderly patients may require a long time to return to their preoperative levels of function.
- Older patients' expectations from surgery may be much different than the expectations of their younger counterparts, and the anesthesiologist must be careful not to judge a patient's decision making based on more typical goals.
- Polypharmacy and drug interaction are a significant problem for older patients.
- Dehydration, elder abuse, and malnutrition (vitamin D, vitamin B12, inadequate caloric intake, poor oral hygiene) are all more common in very old individuals than generally appreciated. Nutritional status is underappreciated as a risk factor for surgery. (Albumin is as sensitive an index for mortality or morbidity as any other single indicator, including the American Society of Anesthesiologists status.)
- Intraoperative Management
- Smaller doses are needed for the induction of general anesthesia in older patients. A given blood level of propofol causes a greater decrease in brain activity in older patients.
- Although swings in blood pressure may not be desirable, there is no evidence that even major, but brief, changes in blood pressure lead to adverse outcomes.
- Whether general or neuraxial anesthesia is used, induction and maintenance of anesthesia commonly result in a significant decrease in systemic blood pressure, more so than typically occurs in younger patients.
- Postoperative Care
- The goals of emergence and the immediate postoperative period are no different for an elderly than a young patient.
- Analgesia is a major goal, and there is no evidence that pain is any less severe or any less detrimental in older patients than in younger ones. Elderly patients sometimes underreport their pain level and may be more tolerant of acute pain.
Table 35-3 Adverse Outcomes Associated with Inadequate Postoperative Pain Relief in Elderly Patients
- Older patients have more difficulty with visual analog scoring systems than verbal or numeric systems. If the patient is cognitively impaired, communication of pain is further impaired; indeed, demented patients often experience severe pain after hip surgery, but even mild cognitive impairment can lead to problems with pain assessment or with use of a patient-controlled analgesia machine.
- Failure to achieve adequate levels of analgesia is associated with numerous adverse outcomes (Table 35-3). The consequences include longer hospitalization and increased incidence of delirium (meperidine should be avoided).
- Epidural analgesia provides analgesia that is superior to IV therapy in elderly patients.
- Delirium often goes undetected in older patients, partly because older patients are less likely to exhibit agitation than young delirious patients.
- Perioperative Complications (Table 35-4)
- Older patients are at increased risk for complications (cardiovascular, pulmonary, renal, central nervous system [CNS], wound infection, death) in the perioperative period, reflecting comorbid diseases and a reduction in organ system reserve because of the aging process.
- Complications of the cardiovascular and pulmonary systems are associated with the greatest perioperative mortality. The higher incidences of the pulmonary complications suggest that greater mortality results from pulmonary complications than cardiac complications.
Table 35-4 The Effects of Age on Selected Perioperative Complications and Associated Mortality*
- CNS complications are also a major source of morbidity and mortality. The incidence of stroke in the general surgical population is approximately 0.5%.
- Age is a risk factor, as is atrial fibrillation, and a history of a prior stroke increases the risk of perioperative stroke by as much as 10-fold.
- Strokes typically occur well after surgery (on average, 7 days later).
- Postoperative cognitive decline and postoperative delirium are significant sources of debilitating morbidity. Although these two entities may prove to be related to each other, at present they appear to be distinct clinical syndromes.
- Postoperative deliriumis an acute confusional state manifested by sudden onset (hours to days) and vacillating levels of attention and cognitive skill. Emergence delirium does not qualify as postoperative delirium.
Table 35-5 Risk Factors for Delirium in elderly patients
- The risk of postoperative delirium after major surgery in older patients is approximately 10%. The risk varies with the surgical procedure and is highest after hip surgery, with an approximate incidence of 35%.
- The cause of delirium is multifactorial (Table 35-5).
- The choice of regional versus general anesthesia does not appear to be a factor, especially if sedation is used in conjunction with the regional technique.
- Delirium is associated with an increased duration of hospitalization and its attendant costs, poorer long-term functional recovery, and increased mortality.
- Postoperative cognitive dysfunctionis characterized by a long-term decrease in mental abilities after surgery. It is inherently more difficult to diagnose than delirium because it usually requires sophisticated neuropsychologic testing, including baseline tests before surgery.
- Compared with nonsurgical control subjects, the cognitive decline lessens over time, with a 25% incidence at 1 week and about a 10% incidence at 3 months.
- At 6 months and beyond, there may be a prevalence of 1% of subjects with cognitive decline.
- Anesthetic management does not appear to affect cognitive decline when comparisons are made between general versus regional anesthesia,
controlled hypotension versus normotension, or IV versus inhalation anesthesia.
- Patient risk factors include age, lower levels of education, and history of stroke even without residual deficit.
- Increased mortality at 1 year is associated with patients who demonstrate cognitive decline at both hospital discharge and at 3 months after surgery.
- The Future
- Improvements in surgical and anesthetic techniques that reduce the overall stress to the patient are permitting more surgeries to be performed on older and sicker patients than ever before.
- The most pressing issues are the prevention of postoperative delirium, cognitive decline, pneumonia, and respiratory failure.
- Improved pain control techniques that also diminish side effects, especially to the brain and bowels, would be welcome.
Editors: Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K.; Cahalan, Michael K.; Stock, M. Christine
Title: Handbook of Clinical Anesthesia, 6th Edition
Copyright ©2009 Lippincott Williams & Wilkins
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