The Geriatric Patient: Age-Related Pathophysiologic Changes and Anesthesia Considerations

Cardiovascular System

The normal aging process affects almost all aspects of the cardiovascular system including the myocardium, the cardiac conduction system, the cardiac valves, and the baroreceptor system. In addition to this normal aging process, it is important to be cognizant of the fact that certain common pathologic conditions such as aortic stenosis, hypertension, and atrial fibrillation can have a compound effect on the physiologic performance of the aging cardiovascular system.

Stiffening of connective tissue and decreased responsiveness to β-receptor stimulation have wide ranging implications for cardiac physiology. Stiffening of connective tissue in the veins, arteries, and myocardium makes them less compliant. Arterial stiffening leads to chronic hypertension and increased afterload, in turn contributing to age-related cardiac myocyte death, which leads to cardiac myocyte and ventricular hypertrophy. This stiffening of the ventricles leads to diastolic dysfunction, impairing early diastolic filling. Impaired venous compliance decreases the body’s ability to compensate for changes in cardiac preload. The increasingly diminished responsiveness of the aging heart and vasculature to β-adrenergic stimulation reduces the contractile response of the myocardium and heart rate to increased demands such as stress and exercise. All of these changes, including the heart’s increased dependency on adequate ventricular filling, increased difficulty in filling stiffer ventricular chambers, and impaired venous compliance in maintaining central circulating volume, culminate in sensitivity to even small decreases in circulating blood volume, resulting in decreased cardiac output. Intraoperative volume losses from hemorrhage, inadequate replenishment, and even preanesthetic prolonged fasting can thus compromise cardiac output during surgery. ^,

Aging also affects the cardiac conduction system and the autonomic nervous system’s response. The maximal heart rate achievable in response to various needs decreases with age and can be estimated as follows:

The aforementioned decrease in β-adrenergic stimulation leads to a concomitant decrease in responsiveness of the baroreceptor mechanism. These changes lead to decreased variability in heart rate, increased incidence of ectopic beats, and an increased incidence of orthostatic hypotension. Arrhythmias such as atrial fibrillation, which can be as common as affecting 1 in 10 individuals older than 80 years of age, can dramatically decrease cardiac output. Atrial fibrillation significantly compromises atrial kick and decreases left ventricular filling, which also results in decreased cardiac output.

Cardiac valves, especially the aortic valve, undergo thickening and calcification with normal aging. Aortic stenosis is more common with age and is present in 12.4% in those 75 years of age and older. ^, Patients with aortic stenosis are dependent on adequate diastolic volume and normal sinus rhythm to maintain myocardial perfusion. Such patients usually have increased left ventricular diastolic pressure, which makes them more susceptible to decreases in coronary perfusion pressure. Avoiding systemic hypotension and tachycardia (with resultant decrease in length of diastole during which coronary perfusion takes place) is therefore paramount in avoiding perioperative cardiac ischemic events.

Respiratory System

With aging, the lung parenchyma undergoes histologic changes akin to emphysema; there is uniform enlargement of air spaces leading to reduced alveolar surface area. This also leads to reduced parenchymal elasticity with the functional effect of decreasing elastic recoil, the passive inward force responsible for decreases in lung volumes during expiration. Osteoarthritic changes associated with aging affect the costovertebral joints and the thoracic spine, leading to kyphosis and height loss caused by dehydration of the intervertebral disks. This remodeling of the chest wall leads to reduced curvature of the diaphragm, the principle muscle involved in respiration. The diaphragm, along with the intercostal muscles and other accessory respiratory muscles, undergoes atrophy and weakening during aging. These anatomic changes that occur with aging result in several mechanical changes relevant to respiratory physiology. Decreased forced vital capacity, decreased pulmonary reserve, increased residual volume, and increased work of breathing all predispose elderly patients to atelectasis. Chronic smoking appears to intensify these age-related changes.

Both peak expiratory and maximal inspiratory flow rates have been observed to decrease with aging. This limitation in airflow gives elderly patients less respiratory reserve to accommodate the increasing needs during heavy to moderate exercise, making their respiratory systems dependent on increasing the frequency of breathing to maintain adequate minute ventilation. The ability to effectively exchange gases in the geriatric respiratory system is also impaired with aging. Early closure of small airways, an increase in overall ventilation-perfusion mismatch resulting from decreased alveolar surface area, and increased pulmonary arterial pressure lead to a gradual decrease in arterial oxygenation and widening of the alveolar-arterial partial pressure of oxygen with age. Regulation of breathing is also affected in the elderly, with an approximately 50% decrease in responsiveness to hypoxia and hypercapnia compared with younger individuals. This is particularly exaggerated during deep sleep, with many geriatric individuals not being able to arouse from REM sleep until their oxyhemoglobin saturations fall below 70%.

Loss of pharyngeal muscular support that occurs with aging, particularly in the hypopharyngeal and genioglossal muscles, predisposes elderly patients to upper airway obstruction. In addition to this, obstructive sleep apnea is also one of the most common sleep-related respiratory disorders found in as many as 50% to 75% of patients older than 65 years of age. These age-related upper airway factors can potentially lead to difficulty maintaining a mask airway and a deterioration in protective upper airway reflexes, particularly in elderly neurosurgical patients who are prone to neurological insult, which can lead to an increased likelihood of pulmonary aspiration.

Useful considerations in combating atelectasis include patient positioning during surgery, active measures (e.g., employing alveolar recruitment strategies during intraoperative mechanical ventilation), postoperative incentive spirometry, early mobilization, judicious use of postoperative CPAP or BiPAP in select patients, and adequate postoperative analgesia. To help mitigate some of the risks posed by the physiologic changes in the aging respiratory system, useful adjuncts during the perioperative phase include using neuraxial or regional anesthetic techniques instead of general anesthesia whenever possible, minimizing the use of neuromuscular blocking agents and ensuring complete reversal of such agents during emergence from anesthesia, avoiding respiratory depression by utilizing opioid-sparing analgesic strategies, and neutralizing stomach acidity with nonparticulate antacid agents.

Renal System

Normal aging processes such as glomerulosclerosis result in renal cortical atrophy and an overall reduction in renal cortical mass. This loss in renal cortical mass is also associated with a functional decrease in glomerular filtration rate (GFR) of approximately 1 mL/min/m ² per year from 40 years of age onward. ^, Although serum creatinine levels in elderly patients may appear within the normal range, the commonly seen reduction in lean muscle mass must be taken in to account, thus a normal creatinine level may, in fact, be masking a reduced glomerular reserve and sensitivity to nephrotoxic insults such as hypoxia and hypovolemia. Age-related changes to the renal system also affect the kidney’s role in drug and metabolite clearance, making geriatric patients more susceptible to accumulations in drug levels such as morphine and meperidine unless appropriately corrected. ^,

Aging also affects the neuroendocrine homeostatic mechanisms of the kidneys, such that the normal renin-angiotensin system’s regulatory responses are more blunted than in younger individuals. This makes elderly patients more susceptible to electrolyte and acid-base disturbances, especially dysnatremias. Hyponatremia is one of the most common electrolyte disturbances seen in the elderly population, with a prevalence of around 11.6% in ambulatory patients. For geriatric neurosurgical patients, this is particularly important if uncorrected; it could lead to reduced seizure thresholds and potentiate cerebral edema.

Urologic diseases are particularly prevalent in the elderly population. Prostate cancer and benign prostatic hypertrophy are common in elderly men, and decreased estrogen levels lead to vaginal atrophy and perineal skin fragility in elderly women, which predisposes both sexes to an increased incidence of urinary tract infections (UTIs). Judicious use of catheters, adequate postoperative analgesia, and promotion of early postoperative ambulation are all vitally helpful measures in preventing UTIs in this vulnerable population.

Gastrointestinal and Hepatic Systems

Physiologic changes in the gastrointestinal system with aging manifest as changes in neuromuscular function, structural changes in the gastrointestinal tract, and functional changes in absorption and secretion.

Neuromuscular degeneration seen with increasing age affects the upper gastrointestinal system including the oropharynx and esophagus, with an impaired ability to coordinate complex reflexes responsible for effective swallowing and peristalsis of food along the esophagus. Failure to coordinate these reflexes can lead to several pathologies such as diffuse esophageal spasm, achalasia, and reflux. In elderly neurosurgical patients, these are important considerations as they increase the risk for perioperative aspiration.

Structural changes in the gastrointestinal tract are seen both in the small bowel and the colon. In the small bowel, it has been observed histologically that there is an age-related decrease in the height of villi, with a resultant decrease in overall surface area available for absorption. In the colon, weakening of the muscularis propria, particularly in areas where blood vessels cross transmurally, are predisposed to the formation of diverticula, thus diverticular disease is one of the most common age-related gastrointestinal diseases contributing to hard stool, constipation, and fecal impaction, and can lead to consequences for the postoperative well-being of surgical geriatric patients.

The liver decreases in both size and function with age, leading to a reduced ability to metabolize drugs and toxins. After 50 years of age, the liver decreases from 2.5% of total body mass to 1.5% as a result of decreased hepatocyte numbers and decreased hepatic blood flow. ^, This reduction in hepatic blood flow reduces the liver’s ability to metabolize drugs cleared by phase 1 pathways such as oxidation, reduction, and hydrolysis through cytochrome P450 pathways. This is important to consider as certain drugs commonly used in anesthetic practice whose clearance is dependent on hepatic metabolism (e.g. ketamine, flumazenil, morphine, fentanyl, sufentanil, and lidocaine) can persist for longer periods in elderly patients.