Healthcare providers have become increasingly focused on pro- viding effective management of acute perioperative pain in all patients, but especially older adults, as the size of this patient population has steadily increased in recent years. Advances in anesthetic and surgical techniques, an improved understanding of the pathophysiology of pain, the development of new opioid and nonopioid analgesic drugs, the incorporation of regional techniques that reduce or eliminate reliance on traditional opi- oid analgesics, and novel methods of drug delivery have all led to greater numbers of older patients undergoing major sur- gery.
An increased prevalence of chronic medical conditions among older individuals may also lead to higher degrees of acute and chronic pain (including acute-on-chronic pain). For instance, acute exacerbations of arthritis, osteoporotic fractures of the spine, cancer pain, and pain from acute medical condi- tions (eg, ischemic heart disease, herpes zoster, peripheral vas- cular disease) must be properly addressed in order to maximize multimodal perioperative pain management. In addition, older individuals are adopting more active lifestyles that can predispose them to trauma and orthopedic injuries that require surgery.
The term elderly encompasses both chronologic and physi- ologic factors. Chronologic age is the actual number of years an individual has lived, whereas physiologic age refers to func- tional capacity or reserve within organ systems defined in pathophysiologic parameters. The chronologic component can be divided into two separate groups: the “young old” (65 to 80 years of age) and the “older old” (greater than 80 years of age).5 Physiologic reserve describes the functional capacity of organ systems to compensate for acute stress and traumatic derange- ments. When present, comorbid disease states such as diabetes mellitus, arthritis, renal insufficiency, ischemic heart disease, and chronic obstructive pulmonary disease (COPD) can all decrease a patient’s physiologic reserve making it difficult for him or her to recover from traumatic or surgical injury.
There are a host of additional factors that may compromise the ability to provide optimal and effective acute pain manage- ment to older patients. A consequence of the comorbid diseases that afflict this patient population with increased frequency is the medications used in treatments for such diseased condi- tions, along with a subsequent increased risk of drug-to-drug and disease-to-drug interactions. An improved understanding of age-related changes in physiology, pharmacodynamics, and pharmacokinetics must be incorporated into any acute pain medicine care plan for older individuals. Altered responses to pain among the elderly population along with difficulties in pain assessment for certain individuals with cognitive dysfunc- tion are potential problems that must also be considered.
Several theories have been advocated to describe the multi- dimensional aspects and consequences of aging that underscore the complexities and difficulties encountered in developing optimal regional anesthetic and analgesic choices for elderly patients. Therefore, the focus of this chapter is to outline the physiologic and pharmacologic implications of aging on surgi- cal anesthesia and acute pain management, as well as the poten- tial risks and benefits of neuraxial blockade along with peripheral nerve/nerve plexus blockade in geriatric patients.
PHYSIOLOGIC CHANGES ASSOCIATED WITH AGING AND CONSIDERATIONS FOR REGIONAL ANESTHESIA/ANALGESIA
Aging is characterized by progressive reductions in the homeo- static reserves of nearly every organ system. Declining organ function, often referred to as homeostenosis, may be gradual or progressive and becomes evident by the third decade of life. The compromised function of each organ system generally occurs independent of changes to other organ systems and may be influenced by a host of factors, including diet, environment, habits, and genetic predisposition. Optimal anesthetic manage- ment using regional techniques in elderly patients depends upon a knowledge and understanding of normal age-related changes in anatomy, physiology, and response to pharmacologic agents. It is also important to distinguish normal physiologic alterations of the central
nervous system (CNS), cardiovascular, pulmonary, and hepatorenal systems from disease-related pathophysiologic changes.
Nervous System Function
Aging results in anatomical and biochemical changes of the brain, spinal cord, and peripheral nervous system (PNS) that result in qualitative and quantitative alterations in function. In addition, advanced age can be associated with decreased brain volume, a manifestation of the loss of neurons, as well as a reduction in cerebral white matter nerve fibers. Specifically, the number of cholinergic and dopaminergic neu- rons declines, and morphologic changes in neuronal fibers occur that result in fewer synaptic contacts and neuroreceptors.
There are a variety of morphological and functional changes in the cardiovascular system associated with aging, including a reduction in left ventricular compliance, generalized hypertro- phy of the left ventricular wall, fibrotic changes of the heart, and decreased myocardial compliance. These changes can result in increased stroke volume and elevated diastolic and systolic blood pressure. Many elderly patients present with cardiac pathology, including moderate to severe coronary artery disease, valvular heart disease, and conduction defects that increase the risk of postsurgical morbidity and death. The effects of aging on cardiac output in the absence of coexisting disease may have minimal influence on the resting individual, but functional changes can become evident with stress and effort-dependent stress. Anesthetics and anesthesia technique may also interact with the patient’s preexisting cardiovascular disease in a manner that may be unfavorable. For example, patients with a fixed cardiac output (as in aortic stenosis) may not tolerate a decrease in systemic vascular resistance associated with neuraxial anesthesia well. Acute/extreme hemodynamic variability in the setting of regional anesthesia, however, can be overcome with careful titration of neuraxial anesthesia with an epidural or spinal catheter and skillful use of vasopressors.
Pharmacokinetic and Pharmacodynamic Changes in the Elderly
Aging affects the pharmacokinetics and pharmacodynamics of medications (eg, sedative/hypnotics, opiates, nonopioid analge- sics, local anesthetics), the physiologic functions of the body, and the composition/characteristics of organs and tissues within the body to variable degrees. The physiologic changes and effects on pharmacokinetics and pharmacodynamics in older patients, as well as some alterations that may be required for drug regimens in older patients. Information in these tables addresses a number of issues related to local anesthetics and opioid analge- sics in view of their widespread use and importance in periop- erative pain management for older patients. The altered response to drugs associated with aging can be highly variable and somewhat unpredictable among individuals and are gener- ally attributable to aging alone, but such responses may be compounded by a higher incidence of degenerative and other coexisting diseases in this patient population.
Multimodal Drug Therapy and the Elderly
A perioperative plan of care that includes a regional technique in an elderly patient must consider the inherent risk of sedation/ hypnosis, multimodal drug regimens, and local anesthetic medi- cations. Safety principles of treatment with analgesic and sedative medications for pain management in older patients, specific to regional and regional peripheral nerve blockade. Sedative drugs (eg,midazolam, propofol) used during block placement should be easy to administer, short-acting, have a high safety margin, and limited adverse effects. Epinephrine can prolong peripheral nerve blockade duration, but caution must be exercised as epinephrine may cause an ischemic neurotoxicity in peripheral nerves with preexisting neuropathy (eg, in patients with diabetes).
Physiology and the Perception of Pain in the Elderly and Clinical Implications
Several review articles have summarized the many age-related changes that occur in pain perception and the neurophysiology of nociception in elderly surgical patients. There are extensive alterations in the structure, neurochemistry, and function of both the PNS and CNS of older patients. Included among these changes is the neurochemical deterioration of opioid and serotonergic systems. Therefore, there may be changes in nociceptive processing, including impairment of the pain inhibitory system, and pain intensity after surgery may be greater or less than otherwise expected from the severity of surgical trauma induced. In one study, older patients matched for surgical procedure reported less pain in the postoperative period, and pain intensity decreased by 10% to 20% for each decade after 60 years of age.