Figure 24.1
Relationship between age and organ function
Physiological Changes with Aging
Cardiovascular System
The cardiovascular system undergoes considerable changes with age and is responsible for most of the perioperative morbidity seen in the elderly. A decrease in arterial compliance leads to an increase in afterload. In response, the left ventricle hypertrophies over time and its compliance decreases. The inability of the left ventricle to relax during diastole is termed “diastolic dysfunction,” which can be quantified by echocardiography. Left ventricular filling then becomes increasingly dependent on preload and atrial contraction. Hence, maintaining sinus rhythm is important to ensure adequate left ventricular filling and cardiac output. The venous vasculature also loses some of its compliance and its ability to act as buffer against volume overload. This predisposes the elderly to pulmonary edema with excessive fluid administration.
Conduction system abnormalities are often seen in the elderly because of a decrease in the number and function of atrial pacemaker cells. The most commonly seen abnormalities are right bundle branch block (RBBB) and first degree heart block. The responsiveness of β-adrenergic receptors is also diminished, rendering the elderly unable to initiate compensatory increases in heart rate in response to hypovolemia. Therefore, the elderly are likely to develop orthostatic hypotension. Although cardiac output may remain unchanged, systolic blood pressure increases with age, whereas diastolic blood pressure increases until age 60–65 years and then plateaus or decreases (see Fig. 24.2). Valvular abnormalities are more common due to sclerosis and calcification, and more than 70 % percent of the elderly have an audible heart murmur.
Figure 24.2
Changes in blood pressure with age
Pulmonary Changes
The major changes that occur with aging can be broadly attributed to the following factors:
blunting of the central nervous system reflexes to hypoxia and hypercarbia
decrease in the compliance of the thoracic wall
decrease in alveolar gas exchange surface
generalized de-conditioning of chest wall musculature
The larger proximal airways tend to dilate with age, causing an increase in dead space. The distal airways tend to collapse, causing an increase in closing volume and air trapping. The compliance of the chest wall decreases (due to stiffening of the costochondral joints). The intercostal spaces are usually decreased because of loss of musculature, which increases the work of breathing and decreases the ability to re-expand atelectatic regions of the lungs. It also hinders the ability to cough and adequately clear secretions.
The central nervous system reflexes in response to hypoxemia and hypercarbia are also diminished. Clinically, all these changes predispose the patients to hypoxemia in the perioperative setting. Finally, the hypoxic pulmonary reflex, which is responsible for shunting blood away from poorly ventilated parts of the lung is diminished, leading to greater ventilation–perfusion mismatching.
Renal Changes
A decline in renal function is seen in the elderly due to a decrease in glomerular filtration rate (GFR) and total renal blood flow (RBF). The serum creatinine may not reflect the extent of renal impairment as muscle mass declines in the elderly. Creatinine clearance can provide a much more accurate reflection of renal function in the elderly. The elderly are also predisposed to dehydration because of diminished compensatory mechanisms, including perception of thirst and the renal response to antidiuretic hormone (ADH) (Table 24.1).
Table 24.1
Renal changes in the elderly
Decrease in renal blood flow |
Decline in glomerular filtration rate |
Decline in ADH response |
Decrease in total body water |
Decreased ability to conserve sodium |
Diminished urine concentrating ability |
Decline in renin-aldosterone levels |
Decreased thirst perception |
Nervous System
With age, there is a decline in higher cognitive functions due to gradual loss of neurons. This loss is more pronounced in the gray matter than the white matter. Additionally, diminished levels of neurotransmitters (dopamine, serotonin and acetylcholine) predispose elderly patients to cognitive deficits which can be accentuated in the postoperative period. Sensory perception such as vision, hearing and taste also diminishes with age.
Postoperative Cognitive Dysfunction and Delirium
Some of the causes of postoperative mental status changes in the elderly are delirium, cognitive dysfunction, perioperative stroke, and electrolyte imbalances
Delirium is a state of confusion with waxing and waning mental status. It commonly presents acutely in the elderly during hospitalization, and frequently in the postoperative setting. There are extrinsic as well as intrinsic causes of postoperative delirium . Intrinsic factors include preexisting cognitive dysfunction and alcohol abuse. Extrinsic factors include the stress of illness and surgery, an unfamiliar environment, medications (e.g., benzodiazepines, narcotics, anticholinergics), underlying infection, urinary retention, pain, and electrolyte imbalances (e.g. hyponatremia). Some of the most important and treatable causes of postoperative delirium are hypotension, hypoxia, and hypercarbia. Table 24.2 outlines the common causes of postoperative delirium.
Table 24.2
Causes of delirium
Advanced age |
Preexisting dementia |
Depression |
Hypoxia and hypercarbia |
Hypotension |
Alcohol or sedative withdrawal |
Impaired vision and hearing |
Metabolic disturbances (hyponatremia/hypernatremia) |
Acute myocardial infarction |
Infection |
Postoperative cognitive dysfunction differs from delirium in that the presentation is not acute. In most patients, there is clinically apparent or subclinical cognitive dysfunction at baseline, which can be elicited during the preoperative examination by performing a simple mini-mental status examination. The incidence of postoperative cognitive dysfunction has been stated to be approximately 30 % in the immediate postoperative period and 12 % after 3 months. Postoperative cognitive dysfunction may be related to increased age, extended duration of anesthesia, low level of education, prior exposure to anesthetics, postoperative infection, respiratory complications, and prior stroke. Patients with postoperative cognitive dysfunction at discharge have been shown to have higher mortality rates during the first year after surgery.
Pharmacokinetic and Pharmacodynamic Changes
With age, there is a progressive change in the constitution of the various body compartments. Total body water diminishes, fat stores increase, and serum albumin decreases. As a result, the volume of distribution of the administered drugs decreases, leading to an increase in drug concentration at the receptor sites. As the lipid stores are increased, lipid-soluble drugs (e.g. morphine) may have a prolonged duration of action. A decline in liver and renal function may also slow down drug metabolism and excretion. Because of these changes, the dosages of most medications should be decreased in the elderly, and the dosing interval should be increased (Table 24.3).
