V_cen = central volume of distribution or initial volume of distribution; a smaller V_cen increases initial plasma levels and enhances transfer of drug in the target organ (brain, muscle).

V. CARDIOVASCULAR AGING (Table 33-2)

VI. PULMONARY AGING

A. 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.

1. 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.

2. These changes, plus a modest reduction in alveolar surface area with age, contribute to a modest decline in resting PaO₂.

B. 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.

C. Generalized loss of muscle tone with age applies to the hypopharyngeal and genioglossal muscles and predisposes elderly individuals to upper airway obstruction.

1. 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.

2. 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

A. Elderly individuals are prone to hypothermia when stressed by modestly cold environments that would not affect younger individuals.

B. 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.

1. 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.)

2. The risks of hypothermia include myocardial ischemia, surgical wound infection, coagulopathy with increased blood loss, and impaired drug metabolism.

VIII. CONDUCT OF ANESTHESIA

A. The Preoperative Visit

1. 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.

2. Elderly patients may require a long time to return to their preoperative levels of function.

3. Older patients’ expectations about 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.

4. Polypharmacy and drug interaction are significant problems for older patients.

5. 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.)

B. Intraoperative Management

1. 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.

2. 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.

3. 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.

C. Postoperative Care

1. The goals of emergence and the immediate postoperative period are no different for an elderly than a young patient.

2. 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.

a. 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.

b. Failure to achieve adequate levels of analgesia is associated with numerous adverse outcomes (Table 33-3). The consequences include longer hospitalization and increased incidence of delirium. (Meperidine should be avoided.)

c. Epidural analgesia provides analgesia that is superior to IV therapy in elderly patients.

3. Delirium often goes undetected in older patients, partly because they are less likely to exhibit agitation than young delirious patients.

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