For the ignorant, old age is winter; for the learned, it is the harvest.
THE elderly population is steadily increasing in both absolute and relative terms as a result of the aging of the baby boomers, healthier lifestyles, and advances in health care. It is estimated that approximately 15% of the U.S. population is older than 64 yr of age, and in the yr 2020, this proportion is likely to be approximately one fifth of the population. Physical function and cognitive dysfunction are reported to predict 5-yr mortality in this population. 1In an attempt to improve function, enhance independence, and increase longevity in the elderly, surgical interventions such as total hip and knee replacements are likely to be performed more frequently in the future. Cognitive declines that may result from surgery and anesthesia are of particular concern in older adults. Therefore, controlled clinical trials that carefully evaluate the long-term outcomes of anesthetic techniques in older adults are of considerable clinical significance. In this issue of ANESTHESIOLOGY, Williams-Russo et al. 2report that elderly patients can safely undergo total hip replacements using a controlled hypotensive epidural anesthetic technique with few cognitive, cardiac, or renal complications.
The hospital admission rate of the elderly, particularly octogenarians, has been increasing dramatically over the last decade. In particular, emergency admissions are more frequent in this age group. Compared with the younger population, postoperative morbidity and mortality seem to be threefold, 3and several studies indicate that age is a major risk factor influencing outcome after surgery. Studies in Veteran Affairs medical centers of patients undergoing abdominal aortic aneurysm repairs show that patients older than 80 yr had a more than twofold higher mortality. 4In these studies, the effects of anesthetic techniques on perioperative outcomes have not been separated from the effects of surgical stress and are worth examining in future studies.
Need for Comprehensive, Long-term Outcome Measures in Anesthesia
The determination of outcomes has become refined in recent years. Strong methodologies, including randomized trials and the use of reliable and valid measures, contribute to our expanding knowledge of the potential benefits and risks of surgery, particularly in vulnerable populations such as the elderly. In this group of patients, the presence of immediate postoperative deficits in cognitive function provokes a question of the permanency and duration of these deficits. Permanent cognitive dysfunction after surgery is of special concern, given the impact these deficits have on all areas of function and, ultimately, the individual's ability to live independently.
The acute effects of anesthetic drugs on cognition and psychomotor functioning are well documented, but the long-term effects of these drugs seem minimal. 5Among the elderly, significant transient cognitive dysfunction often occurs up to 1 week after surgery, but longer-term impairments are less common. 6–7A consistent exception occurs after cardiopulmonary bypass: neuropsychological declines, both short- and long-term, occur frequently in older adults. 8Because intraoperative hypotension is associated with greater cognitive decline after coronary artery bypass surgery, 9the possibility that hypotensive anesthesia during hip replacement may induce some degree of cognitive decline is an important issue to investigate. Williams-Russo et al. 2used sophisticated measures of cognitive functioning to examine the potential short- and long-term impact of hypotensive anesthesia. The tests were carefully selected to measure major domains of function—language, psychomotor speed and attention, and memory—in elderly patients across time. These widely used neuropsychological tests are performance-based rather than subjective and show excellent psychometric properties, including test–retest stability and validity. The strength of the study design, including the range of sensitive measures, the size of the sample, the elevated risk of the population, and longitudinal assessments, increases confidence in their conclusion.
Anesthetic Considerations in the Elderly
The anesthetic treatment of elderly patients presents special challenges that relate to the physiologic process of aging, the numerous coexisting age-related diseases, and the variety of pharmacologic agents that are often prescribed to treat chronic ailments. 10It has been suggested that, as part of the “normal” aging process, most organ systems lose approximately 1% function per year, beginning at approximately age 30. However, more recent studies suggest considerable individual variability in these declines. Studies suggest that the hallmark of aging is not necessarily decrements in resting level of performance, but in the lack of functional reserve and inability of the endocrine and cardiovascular systems to respond to external stress. Aging organ systems may not have the functional reserve to meet with the increased demands associated with the stress of surgery. In addition to the well-known physiologic changes in the cardiovascular, renal, and pulmonary systems associated with aging, age-related changes occur in cognitive abilities, particularly memory and speed of information processing. It is encouraging to note in the study by Williams-Russo et al. 2that older adults tolerated the stresses of anesthesia and hypotension with complication rates comparable to normotensive anesthesia.
The advantages of any anesthetic technique need to be balanced against the associated risks. For example, with hypotensive anesthesia, the advantages of reduced blood loss need to be balanced with the possibility of decreased cerebral perfusion and subsequent cognitive impairment. Several studies suggest a connection between low blood pressure and increased mortality in people older than 75 yr. In addition, blood pressure levels show a complicated relationship with cognitive impairment. Elevated rates of cognitive decline have been associated with both low and high blood pressures, 11with the pattern of decline depending on the nature of the blood pressure change with age. 12Among the elderly, orthostatic hypotension has been shown to be a risk factor for cognitive decline. 13,14The lack of any short- or long-term cognitive impairment in the study by Williams-Russo et al. 2with the use of hypotensive epidural anesthesia is encouraging, suggesting the safety of these transient episodes of low blood pressure.
Cerebral blood flow distribution during hypotension may vary depending on the technique used. For example, hemorrhage and trimethaphan uniformly decreased cerebral blood flow in most tissues. In contrast, nitroprusside-induced hypotension maintains regional blood flow in cortical and telencephalic regions. 15Thus, the effects of different hypotensive techniques on cerebral blood flow and cognition may not necessarily be similar.
Caution in Generalizing Conclusions of the Study
There are certain aspects of the study by Williams-Russo et al. 2that may limit the generalizability of their conclusions. The authors excluded patients with significant carotid stenosis or valvular heart disease. In addition, the patient's hemodynamic status was monitored invasively with arterial and central venous lines, and the hypotensive epidural anesthesia was accompanied by a continuous infusion of low-dose epinephrine. In an earlier study, Sharrock et al. 16demonstrated that low-dose epinephrine infusion preserved cardiac output during hypotensive epidural anesthesia in elderly patients. Hence, hypotensive anesthesia in the elderly using other techniques may not be equally safe and needs to be confirmed with additional studies.
In summary, this study confirms that age alone is not a contraindication to hypotensive anesthesia. Few cardiovascular, renal, and thromboembolic complications and no declines in cognitive function were found in an elderly at-risk population. Anesthesiologists have focused their attention mostly on immediate perioperative outcomes, particularly those related to organ function and mortality. The careful longitudinal follow-up performed by Williams-Russo et al. that extended well beyond the perioperative period is worth emulating in future studies.