In the absence of coexisting disease, resting systolic cardiac function seems to be preserved, even in octogenarians. Increased vagal tone and decreased sensitivity of adrenergic receptors lead to a decline in heart rate.
Elderly patients undergoing echocardiographic evaluation for surgery have an increased incidence of diastolic dysfunction compared with younger patients.
Diminished cardiac reserve in many elderly patients may be manifested as exaggerated decreases in blood pressure during induction of general anesthesia. A prolonged circulation time delays the onset of intravenous drugs, but speeds induction with inhalational agents.
Aging decreases the elasticity of lung tissue, allowing overdistention of alveoli and collapse of small airways. Residual volume and the functional residual capacity increase with aging. Airway collapse increases residual volume and closing capacity. Even in normal persons, closing capacity exceeds functional residual capacity at age 45 years in the supine position and age 65 years in the sitting position.
The neuroendocrine response to stress seems to be largely preserved or, at most, only slightly decreased in healthy elderly patients. Aging is associated with a decreasing response to β-adrenergic agents.
Impairment of Na+ handling, concentrating ability, and diluting capacity predispose elderly patients to both dehydration and fluid overload.
Liver mass and hepatic blood flow decline with aging. Hepatic function declines in proportion to the decrease in liver mass.
Aging produces both pharmacokinetic and pharmacodynamic changes. Disease-related changes and wide variations among individuals in similar populations prevent convenient generalizations.
The principal pharmacodynamic change associated with aging is a reduced anesthetic requirement, represented by a reduced minimum alveolar concentration (MAC).
Elderly patients display a lower dose requirement for propofol, etomidate, opioids, benzodiazepines, and barbiturates.
The elderly patient typically presents for surgery with multiple chronic medical conditions, in addition to any acute surgical illness. Age is not a contraindication to anesthesia and surgery; however, perioperative morbidity and mortality are greater in elderly than younger surgical patients.
As with pediatric patients, optimal anesthetic management of geriatric patients depends upon an understanding of the normal changes in physiology, anatomy, and response to pharmacological agents that accompany aging. In fact, there are many similarities between elderly and pediatric patients (Table 43–1). Individual genetic polymorphisms and lifestyle choices can modulate the inflammatory response, which contributes to the development of many systemic diseases. Consequently, chronologic age may not fully reflect an individual patient’s true physical condition. The relatively high frequency of serious physiological abnormalities in elderly patients demands a particularly careful preoperative evaluation.
TABLE 43–1Similarities between elderly people and infants, compared with the general population. |Favorite Table|Download (.pdf) TABLE 43–1 Similarities between elderly people and infants, compared with the general population.
Decreased ability to increase heart rate in response to hypovolemia, hypotension, or hypoxia
Decreased lung compliance
Decreased arterial oxygen tension
Impaired ability to cough
Decreased renal tubular function
Increased susceptibility to hypothermia