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.

Respiratory System

As the respiratory system ages, the lungs become less compliant and the muscles involved in respiration weaken. Central responses to hypercapnia and hypoxia are blunted, which puts patients at increased risk for pharmacologic-induced respiratory depression. The incidence of both restrictive and obstructive lung disease and sleep apnea increase with age.

With the aging process, the diaphragm weakens and the chest wall stiffens because of calcification of intercostal cartilage. There are also arthritic changes in the costovertebral joints, weakening and atrophy of the intercostal muscles, and height loss due to osteoporosis and/or kyphosis. Lung compliance increases as elastic recoil decreases despite increased elastin production. Therefore while total lung capacity remains unchanged, functional residual volume increases 5% to 10% per decade, leading to an overall decrease in vital capacity. Aging is also associated with alveolar airspace increases similar to those seen in emphysema, decreased gas exchange, and increased ventilation-perfusion (V-Q) mismatch. Mechanical changes include decreased vital capacity, decreased pulmonary reserve, increased work of breathing, and increased residual volume, all of which predispose older adults to atelectasis. Closing capacity, the point at which small airways close, increases with age. Functional residual capacity (FRC) is reduced relative to closing capacity, which may result in atelectasis, pulmonary shunting, and hypoxemia. Certain common intraoperative conditions, such as increased intraabdominal pressure due to carbon dioxide insufflation or Trendelenburg positioning, reduce the FRC and lung compliance. Strategies to minimize atelectasis in the postoperative period include early mobilization/ambulation after surgery, chest physiotherapy, and incentive spirometry.

Compared to younger patients, older patients also have weaker pharyngeal muscles, decreased clearance of secretions, decreased mucociliary transport, less efficient coughing, decreased esophageal motility, and less effective protective upper airway reflexes. Together, these factors place the older population at increased risk for aspiration and postoperative pneumonia. Anesthesiologists can implement four specific strategies to reduce the risk of aspiration and other pulmonary complications. First, using neuraxial or regional anesthesia with minimal sedation in lieu of general anesthesia (when possible) can reduce the risk of aspiration by reducing anesthetic-induced interference with the cough reflex. Second, avoiding intermediate and long-acting neuromuscular blocking agents, and ensuring adequate reversal of neuromuscular blockade, can also help reduce aspiration and postoperative pneumonia risk. Residual neuromuscular blockade is a particular concern in older patients with reduced pulmonary function. Third, respiratory depressants such as opioids can lead to hypoventilation and respiratory acidosis, which further potentiates the effects of neuromuscular blocking agents. When appropriate, opioid-sparing analgesic strategies can be helpful in older patients. Fourth, neutralization of stomach acid with nonparticulate antacids (such as sodium citrate) can be helpful in preventing chemical pneumonitis and pulmonary injury in case aspiration does occur.

In addition to mechanical changes, older adults have an approximate 50% decrease in the respiratory response to hypoxia and hypercarbia, which is even more pronounced during sleep. Some geriatric patients may not awaken from rapid eye movement sleep until oxygen saturation decreases significantly (e.g., to 70% or lower). The most common sleep-related respiratory derangements in older adults is sleep apnea, which may affect 50% to 75% of patients over age 65. Older patients tend to have decreased hypopharyngeal and genioglossal muscle tone, which predisposes them to upper airway obstruction, particularly during sleep. Patients can be screened preoperatively for obstructive sleep apnea (OSA) using one of several screening questionnaires such as the STOP-Bang, Berlin, or American Society of Anesthesiologists (ASA) questionnaires. Patients with OSA should be recognized as having a potentially difficult mask airway and postoperatively may benefit from continuous positive airway pressure and opioid-sparing management.

Renal System

After 50 years of age, average kidney weight decreases from approximately 250 g to 180 g, mostly as a result of cortical atrophy from glomerulosclerosis. Along with this loss of renal cortex, the glomerular filtration rate (GFR) decreases by about 1 mL/min/m ² per year starting at 40 years of age. Chronic diseases frequently found in the older population (e.g., hypertension, diabetes mellitus, and atherosclerosis) can exacerbate this normal age-related decline in renal function. Although elderly patients typically have normal serum creatinine levels, they also tend to have decreased lean muscle mass and lower creatinine overall. Therefore a “normal” serum creatinine in an older patient may belie a reduced glomerular filtration reserve and obscure the resulting renal sensitivity to ischemic and nephrotoxic injuries. Specifically, in the setting of reduced GFR, medications that are excreted through the kidney may accumulate if the dose is not appropriately adjusted.

In addition to reduced GFR, blunted responses to aldosterone, vasopressin, and renin also reduce the older patient’s ability to adjust volume status and may result in electrolyte and acid-base derangements. In particular, older adults are susceptible to dysnatremias; hyponatremia affects 11% of the geriatric ambulatory community and 5.3% of hospitalized geriatric patients. Hypernatremia affects 1% of hospitalized patients age 60 and older. Further, because older adults often have inappropriate sodium excretion, they are particularly prone to hypotension and acute kidney injury in the setting of hypovolemia.

The incidence of urologic disease (i.e., bladder and prostate) also increases with age. The incidence of postoperative urinary retention increases in older men and women. This is an important point to recognize because discomfort due to urinary retention can be a common cause of postoperative agitation. Urinary tract infections (UTI) also increase in incidence in older men and women. Elderly women may have skin breakdown in the genital area because of vaginal atrophy from decreased estrogen, which increases the risk of UTI. In addition, the incidence of pelvic prolapse in women increases with age and also increases the risk of UTI.

Gastrointestinal and Hepatic Systems

The size and function of the liver decrease with age, which affects hepatic drug metabolism. After age 50, the liver decreases from 2.5% of total body mass to 1.5% in part due to fewer hepatocytes and decreased blood flow. Despite having fewer hepatocytes, healthy older adults typically have normal liver synthetic function, though they have reduced reserve under stress. Similarly, hepatic blood flow decreases with age such that the average 65 year old has 40% less hepatic blood flow than the average 25 year old. Older populations may more slowly metabolize drugs that are cleared by phase-1 pathways (e.g., oxidation, reduction, and hydrolysis through the cytochrome P450 system) because of decreased hepatic blood flow, but phase II metabolism (e.g., acetylation and conjugation) does not seem to be affected by age. Anesthesiologists should be aware that older adults are slower at clearing high extraction drugs whose clearance depends directly on hepatic blood flow (e.g., ketamine, flumazenil, morphine, fentanyl, sufentanil, and lidocaine).

The incidence of postoperative nausea and vomiting decreases with age, which is fortunate because many antiemetics act through anticholinergic and/or antihistaminergic mechanisms, which can cause altered mental status and delirium. The Beers criteria recommend against most of these medications as they increase the risk of delirium. Specifically, the Beers criteria recommend avoiding prochlorperazine, promethazine, metoclopramide (except in the setting of gastroparesis), and corticosteroid prophylaxis. The 5-HT3 receptor antagonists (e.g., ondansetron), are a better choice for older adults, although the 5-HT3 antagonists contribute to QTc interval prolongation.

The incidence of some hepatic and gastrointestinal pathologies increases with age. For example, the incidence of nonalcoholic fatty liver disease (NAFLD) increases with age, affecting nearly half of geriatric patients; however, in contrast to younger populations, it is unclear whether NAFLD is associated with metabolic syndrome, cardiovascular disease, or cirrhosis when it is first diagnosed at an advanced age. That said, as the obese diabetic patients with NAFLD age and become geriatric patients, they have an increased risk of complications, such as severe hepatic fibrosis, hepatocellular carcinoma, and cryptogenic cirrhosis. Whereas hepatic pathology certainly impacts anesthetic management, other common gastrointestinal disorders of older adults, such as diverticulosis and cholelithiasis, typically do not.

Musculoskeletal System

As with other organ systems, the aging musculoskeletal system undergoes changes relevant to anesthesiologists. Among the well-functioning older adult, lean muscle mass declines by roughly 1% annually while muscle strength declines by roughly 3% annually, meaning muscle function and quality decreases faster with age than muscle quantity does. Maintaining strength in the perioperative period is critical in older people. Declining muscle strength is associated with increased mortality risk, and older adults lose muscle mass much faster than their younger counterparts. For example, healthy older adults who were placed on bedrest for 10 days experienced greater loss of muscle mass than healthy younger adults who were placed on bed rest for 28 days.

Decreased lean muscle mass can prove misleading among older patients, whose weight may remain stable, while their total body fat increases and their subcutaneous (insulating) fat reserves decrease. A 10-year longitudinal study of older adults showed a 23% per decade decline in subcutaneous fat with a concurrent average 11% per decade increase in total body fat. Diminished subcutaneous fat thickness and age-related dysregulation of cutaneous circulation help to explain why older patients are much more prone to temperature dysregulation intraoperatively even though the basal core temperature of the elderly (aged 65-95) is only about 0.4°C (0.7°F) lower than that of other adults (aged 25-64). Age-related dysregulation of the cutaneous microcirculation also contributes to impaired wound healing. Anesthesiologists can optimize surgical healing in this population by maintaining adequate hydration, normothermia, and good tissue oxygenation.

Along with age-related changes in the muscles and skin, aging affects the skeletal system as well. Osteoarthritis affects about half of those aged 75 and older and can lead to limited joint mobility in older patients. Anesthesiologists should be aware of this and inquire about this with older patients to avoid exacerbating preexisting joint issues while positioning the patient in the operating room.

Central Nervous System

Changes in the aging central nervous system can give rise to a host of age-related concerns, such as cognitive decline, memory loss, sleep derangements, dementia, movement disorders, depression, and an increased risk of delirium. Although the number of neurons in the brain does not decrease in normal aging, older brains have fewer dendrites and synapses, which contributes to decreased brain volume and to decreased neuronal connectivity, particularly in the hippocampus, frontal/prefrontal cortex, and the temporal lobe. Specifically, magnetic resonance imaging studies have shown that cortical gray matter thins at a rate of 0.5% to 1% per year in the geriatric brain. Further, age-related dysregulation of neuronal transmission, baseline neuronal firing, calcium metabolism, and gene expression diminishes both connectivity and plasticity. Functionally, these physiologic changes contribute to normal, age-related cognitive decline in many domains such as executive function, cognitive processing speed, working and spatial memory, and maintenance of circadian rhythm. Of particular relevance to anesthesiologists, these age-dependent decreases in cognitive reserve may manifest as increased sensitivity to anesthetic medications, an increased risk of postoperative cognitive dysfunction and delirium, and a decrease in function.

Specifically, in dementia, the decline in memory and cognition becomes severe enough to interfere with daily activities whereas in mild cognitive impairment, cognitive decline is measurable and noticeable, but does not interfere with one’s ability to perform daily activities. Frank neuron loss typically occurs in dementia, regardless of the dementia subtype. In Alzheimer disease, a complex interplay between abnormal tau and beta-amyloid proteins seems to precipitate global neuronal cell death while in vascular dementia, neuronal cells die because of hemodynamic compromise, leading to a step-wise decline in cognitive function. Finally, in Lewy body dementia abnormal α-synuclein deposits give rise to neuronal death. Overall, dementia increases dramatically in prevalence with advancing age in a step-wise manner ( Fig. 65.3 ), affecting nearly two-thirds of patients over the age of 90 years.

Global prevalence of dementia by age.

Redrawn from Prince M, Bryce R, Albanese E, et al. The global prevalence of dementia: a systematic review and metaanalysis. Alzheimers Dement. 2013;9:63–75.

Dementia presents challenges for anesthesiologists, particularly regarding pain management. For example, patient-controlled analgesia may not be an option. Opioid administration is often difficult to titrate in these patients, and patients may not be able to cooperate with regional anesthesia. Further, patients with dementia may also develop concurrent delirium, which can be difficult to disambiguate from underlying dementia. Similarly, Parkinson disease presents a particular challenge for the anesthesiologist. Patients with Parkinson disease are more prone to developing immobility and thus deep venous thrombosis; dysphagia and respiratory dysfunction and thus aspiration and pneumonia; urinary retention and thus UTI; and psychiatric complications and thus delirium. Drug interactions can be a particular concern in patients with Parkinson disease. For example, many antiemetic drugs such as metoclopramide and promethazine antagonize dopamine and may worsen extrapyramidal symptoms. Inhibitors of the enzyme monoamine oxidase (MAO)-B, which are frequently used in Parkinson disease, can predispose patients to serotonin syndrome, particularly if used in conjunction with certain opiates such as tramadol. Propofol can induce dyskinesia in this population, which can be managed with dexmedetomidine.

Mood disorders, particularly depression, are often underrecognized in older adults. Minor depression affects approximately 7.7% of geriatric primary care patients, approximately 14.4% of geriatric patients in hospital settings, and nearly 20% of those with minor cognitive impairment. Depression predisposes patients to postoperative cognitive dysfunction (POCD), in-hospital delirium, major adverse cardiac events, increased postoperative analgesic use, and suboptimal postoperative outcomes. Discussion of mood symptoms prior to anesthesia can help to inform perioperative management and the use of antidepressant medications. Typically, antidepressants are continued during the perioperative period because of the risks of “discontinuation syndrome” and because of their benefits for pain management ; however, MAO inhibitors can lead to severe hypotension in the setting of sympathetic stimulation or in conjunction with sympathomimetic drugs. Even selective serotonin reuptake inhibitors, the most commonly used and “safest” antidepressants, have been associated with a higher risk of in-hospital mortality, bleeding, and readmission.

Finally, delirium and POCD are two common postoperative complications in older patients. Each of these topics have dedicated chapters in this text, so they are only briefly reviewed here. Delirium, which affects about 10% of older postoperative patients overall and 60% to 80% of intensive care unit (ICU) patients, manifests as acute, fluctuating confusion with altered attention and awareness that cannot be better explained by preexisting or developing dementia. Common delirium screening tools include the Confusion Assessment Method (CAM) and the CAM-ICU for ventilated ICU patients. Few treatments for delirium have proven efficacious; however, management of underlying medical conditions (e.g., electrolyte imbalances, infections), modifying risk factors (e.g., reducing sleep deprivation, increasing mobility, giving patients their glasses and hearing aids, ensuring good hydration), and avoiding or limiting medications known to trigger delirium (e.g., benzodiazepines, dihydropyridines, antihistamines, opioids) may prove beneficial. In contrast to delirium, POCD is a syndrome defined by worsening performance on neuropsychologic tests postoperatively compared to a perioperative baseline. Overall, this decline in cognitive performance across multiple domains presents days to weeks after surgery and is associated more strongly with age than any other risk factor. By and large, POCD resolves within months of both cardiac and noncardiac surgery; however, individual patients may follow different trajectories with declines remaining up to 5 years or longer.

Cognitive Assessment and Delirium Risk

In the immediate perioperative period, occult preoperative cognitive impairment in older adults is common; the incidence is more than 20% of patients over 65 years of age presenting for presurgical testing with the highest prevalence in the oldest patients. However, talking with patients and families about cognitive health before and after surgery is a new challenge for anesthesiologists. In 2016, the ASA launched the Brain Health Initiative, which is a “low barrier access program to minimize the impact of preexisting cognitive deficits, and optimize the cognitive recovery and perioperative experience for adults 65 and over….” The basic principles of the program include screening for preoperative cognitive impairment and that anesthesiologists lead discussions regarding the potential for postoperative delirium and cognitive dysfunction.

The cognitive assessment of patients prior to surgery can be challenging. In-depth neuropsychiatric testing is not practical for most pretesting centers since it often involves an hour or more of tests administered by a trained individual. More practical for the presurgical arena is the use of brief screening tools that are meant to identify patients who are likely to have cognitive impairment ( Table 65.1 ). A recent large study suggests that cognitive screening in a pretesting clinic is practical and well accepted by patients and staff members. An obvious but difficult question for anesthesiologists is how to proceed when a patient is identified as likely to have cognitive impairment. Informing patients and offering them postsurgical follow-up with an expert in cognition is important. The same study showed that patients believe that screening before surgery is important and that they want to know their results. Baseline cognition is also important for delirium-risk stratification; patients with cognitive impairment are at higher risk and therefore may benefit the most from delirium prevention programs. Additionally patients, caregivers, and the perioperative team should have this information since these patients are more likely to require a higher level of care after surgery such as a skilled nursing facility. The ACS guidelines strongly recommend performing cognitive assessment early in the patient evaluation because impairment suggests that medication information and functional status reporting may be unreliable, although in the latter there is some evidence to the contrary.

Although preoperative cognitive impairment is a risk factor for the occurrence and severity of postoperative delirium, it is not the only risk factor. There are several delirium-risk prediction indices and examples of two delirium prediction tools are listed in Table 65.2 . Whereas each index is a bit different, most include age, cognitive status before surgery, then some index of medical illness, and the invasive nature of the surgery.

Functional/Frailty Screening

Frailty is a common and morbid condition found with a higher prevalence in older adults before surgery (25%-56%) than in community-dwelling elders (10%). Frailty has been conceptualized in two major ways: one includes decreased reserve to physiologic stress and is characterized by decline across organ systems; and the other is an accumulation of deficits, that is, the accumulation of comorbid states that can result in overall physiologic vulnerability. Frailty has been shown to correlate with poor postoperative outcomes (death, complications) in a wide range of major surgeries.

Although frailty is a geriatric syndrome it does not need to be measured by a geriatrician. The classic frailty phenotype measured by Linda Fried did require expertise; however, there are now several validated frailty screening tools. It is not clear which of the screening tools best measures frailty and the answer may vary for different populations and settings. For instance, a frailty screen that includes grip strength may not be best suited for a cervical spine population that often has cervical myelopathy. The preoperative testing facility may dictate the type of assessment possible; some preoperative clinic areas are not suitable for a 5-meter gait speed test. Table 65.3 has examples of frailty assessment tools.

Table 65.3

Frailty Assessment Tools and Scoring Systems in Current Literature

From Amrock LG, Deiner S. The implication of frailty on preoperative risk assessment. Curr Opin Anaesthesiol . 2014;27[3]:330–335.

Frailty Measure	Description	Clinical Outcome	Source
Frailty phenotype	Weight loss, grip strength, exhaustion, low physical activity, and 15 feet walking speed	30 days postoperative complications, institutionalization, and length of stay	Makary et al. Revenig et al.
Frailty index/deficit accumulation	30-70 measures of comorbidity, ADL, physical and neurological exam	Mortality and institutionalization	Mitnitski et al. Rockwood et al.
Modified frailty index	History of diabetes, COPD or pneumonia; congestive heart failure; myocardial infarction; angina/PCI; hypertension requiring medication; peripheral vascular disease; dementia; TIA or CVA; CVA with neurological deficit; ADL	30-day, 1-year, and 2-year mortality, 30-day major postoperative complications	Adams et al. Farhat et al. Karam et al. Obeid et al. Patel et al. Tsiouris et al. Velanovich et al.
Gait speed	5-m gait ≥6 s	Mortality, major postoperative complications, institutionalization, and length of stay	Afilalo et al.
Timed up and go	TUG ≤10 s; 11-14 s; ≥15 s	1-year mortality	Robinson et al.
Falls	6-month hx of falls	30-day major postoperative complications, institutionalization, and 30-day readmission	Jones et al.
Robinson	Katz Score, Mini cognition, Charlson Index, anemia <35%, albumin <3.4, hx of falls	30-day major postoperative complications, length of stay, 30-day readmission, 6-month postoperative mortality	Robinson et al.

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