Figure 56-1. Annual rate of anesthesia per 100 population within the different age groups from 1980 to 1996 in France (Reprinted, with permission, from Clerque F, Auroy Y, Pequinot F, et al: French survey of anesthesia in 1996. Anesthesiology 1999;91:1509).

        DEFINITION OF AGING

To effectively treat elderly patients, clinicians must have an understanding of aging, how it occurs, how it affects specific organ systems, and how it influences clinical care when a patient is subjected to surgery. Aging is a normal phenomenon, although the basic mechanisms that cause aging are still poorly understood. Aging per se is represented by those manifestations of irreversibly altered organ function that are common in all elderly persons and are usually progressive. The physiologic process of aging varies considerably from person to person; hence variation in organ capabilities increases with age. Different organs in the same individual may age at different rates; each system has its own temporal pattern of age change. The organ reserves, which are so essential to ensure homeostasis, gradually decrease, resulting in an increased sensitivity to internal and external environmental stressful stimuli³ (Figure 56-2).

        INCREASING AGE & RISK OF ANESTHESIA-RELATED PERIOPERATIVE COMPLICATIONS

Age alone is not a major factor in predicting the risks to a patient undergoing anesthesia and operation. The overall physical status or disease state or both are better predictors of outcome. Risk is directly related to the number and extent of coexisting preoperative diseases. Ischemic heart disease, diabetes mellitus, and hypertension are the preoperative conditions most indicative of a higher risk of peri- and postoperative morbidity and mortality.⁴ The type of operation appears to be important; upper abdominal surgery procedures are associated with the highest morbidity and mortality, followed by open-heart surgery procedures. The importance of the site as a major determinant of perioperative risk in the elderly applies equally to both emergency and elective surgery. The anesthetic complication rate increases very little with advancing age in the absence of coexisting disease. As a group, elderly surgical patients are at increased risk of perioperative morbidity and mortality because of the high incidence of coexisting diseases. One third of older patients have three or more preexisting diseases or complicating conditions, and four fifths have at least one complicating condition. Underlying medical diseases and the type, duration, and urgency are more important predictors of outcome than chronologic age.

Figure 56-2. Effects of aging on organ function (Reprinted, with permission, from Williams ME: Clinical implications of aging physiology. Am J Med 1984;76:1049).

Clinical Pearlss

        AGE-RELATED ANATOMIC & PHYSIOLOGIC CHANGES OF SIGNIFICANCE TO THE ADMINISTRATION OF REGIONAL ANESTHESIA

Central & Peripheral Nervous Systems

The central and peripheral nervous systems degenerate with advancing age. The diameter of the myelinated fibers in the dorsal and ventral roots becomes smaller, and the number of these fibers decreases. By the age of 90 years, more than one third of the myelinated nerve population has disappeared. The connective tissue sheaths that cover the nerve tissues become weakened by the general deterioration in the mucopolysaccharides of the ground substance, allowing local anesthetic solution to penetrate the sheaths more readily.⁵ These changes may affect the neural block characteristics and the pharmacology of local anesthetic agents. However, currently, it is well understood how these changes may affect pharmacodynamics of neuraxially or perineurally administered local anesthetics.

Clinical Pearls

        The abovementioned factors are accelerated by arteriosclerosis and diabetes, both of which cause premature aging. After the third decade, there is a steady slowing of the conduction velocity in peripheral nerves, especially in motor nerves.⁶ The dura becomes more permeable to local anesthetic agents because of a significant increase in the size of the arachnoid villi.⁷ This change is accompanied by a decrease in the thickness of the root dura. Aging is possibly associated with a reduction in the volume of cerebrospinal fluid (CSF) and with an increase of the specific gravity of the CSF, both of which may influence the distribution of intrathecally injected local anesthetics.⁸

Autonomic Nervous System

Changes in the autonomic nervous system with age may alter the course of a regional anesthetic block. Normal aging is associated with a progressive impairment of autonomic homeostasis, that is, there is a delayed restabilization during hemodynamic stress.⁹ Aging is accompanied by a variety of neurohormonal changes. One example is that tonic parasympathetic outflow declines, while the basal sympathetic nervous system activity increases. Elderly people respond to stresses of different degrees with a larger increase in norepinephrine levels. The beta-receptor affinity for adrenergic agonists and antagonists appears to be blunted, probably because of a reduced affinity of the beta-receptor for agonists.¹⁰ The changes in autonomic function are referred to as physiologic beta-blockade.

Clinical Pearls

        Baroreceptors are autonomic reflex responses that maintain cardiovascular homeostasis. Their sensitivity declines progressively with age,¹¹ resulting in reduced compensatory blood pressure and heart rate responses when the carotid blood pressure alters. These factors are of clinical importance when the sympathetic blockade or central neural blockade is associated with a decrease in systemic blood pressure.

Cardiovascular System

Aging is associated with a variety of morphologic and functional changes of the cardiovascular system.⁹ With aging, the large arteries progressively lose elasticity. This loss of elasticity leads to increased systolic pressure, which results in increased afterload for the left ventricle and finally, to mild generalized hypertrophy of the left ventricular wall, which is characterized by increased end-diastolic left ventricular volume.¹² The diminished elasticity and fibrotic changes of the heart muscle make the aged heart noncompliant and thus both volume-sensitive and volume-intolerant. All of these observations have important clinical impiications for the treatment of patients undergoing regional anesthesia.

Clinical Pearls

        The elderly are unable to respond to stress by significantly increasing the left ventricular ejection fraction. In elderly patients, cardiac output is maintained by increasing end-diastolic volume, which results in increased stroke volume.¹² Elderly patients may, therefore, not maintain blood pressure as effectively as younger patients when challenged by relatively minor hypovolemia and additional cardiovascular stress. These factors have considerable importance when administering neuraxial anesthesia. Sympathetic blockade can result in severe hypotension in the setting of hypovolemia.

        CENTRAL NEURAL BLOCKADE

Epidural Anesthesia

Older age is associated with a higher upper level of analgesia after thoracic and lumbar epidural administration of a fixed dose of a local anesthetic solution^13–15 (Figure 56-3, Table 56-1). The influence of age on the upper level of analgesia varies with different volumes and also depends on variability between individuals.

        Higher levels of analgesia with advancing age are attributed to reduced leakage of local anesthetic solution because of progressive sclerotic closure of intervertebral foramina.¹⁶ In the younger individual, the areolar tissue around the intervertebral foramina is soft and loose. In the elderly, the areolar tissue becomes dense and firm, partially sealing the intervertebral foramina. As the fatty tissue degenerates and the content reduces with advancing age, the epidural space becomes more compliant and less resistant; this may also contribute to the greater longitudinal spread of injected solutions in elderly patients.¹⁷ The clinical course of epidural anesthesia may be influenced by a shift in the site of action, from a predominantly paravertebral site in the young, to a subdural or transdural site in the elderly. The shift may be caused partly by an increased permeability for local anesthetics of the dura because of an increased size of the arachnoid villi.⁷ With increasing age, changes in the connective tissue ground substances may result in changes in local distribution, that is, in the distribution rate of the local anesthetic from the site of injection (the epidural space) to the sites of action.¹⁶

Figure 56-3. Relationship between the upper level of analgesia and age after epidural administration of 0.5% bupivacaine (Reprinted, with permission, from Veering BT, Vurm AGL, Van Kleef JW, et al: Epidural anesthesia with bupivacaine: Effets of age on neural blockade and pharmacokinetics. Anesth Analg 1987;66:589).

↑ increased; ↓ decreased; ≈ unchanged.

        In older patients the onset time to maximal caudad spread and motor blockade decreases together with an enhanced intensity of motor blockade following epidural administration of bupivacaine.¹³ With the relatively new, long- acting local anesthetic agents ropivacaine and levobupivacaine, the spread of analgesia and the intensity of motor block increases with advancing age as well.^14,15

        Often, epinephrine is used in the epidural test dose as a marker of intravascular injection. A given dose of epinephrine may be less reliable in older patients, owing to decreased ß-adrenergic responsiveness.¹⁸ Lumbar epidural anesthesia with lidocaine does not affect the resting ventilation parameters, such as minute ventilation and tidal volume, in older patients or stimulate the ventilatory response to hypercapnia to the same degree as in younger patients.¹⁹ Therefore, lumbar epidural anesthesia appears to be a suitable alternative technique in elderly patients. To limit the extent of analgesic and sympathetic blockade after epidural administration, the dose should be reduced. The relationship between the epidural segmental dose requirement and the analgesic spread is not linear and still unclear in older patients. Further studies are required to determine the optimum dose to provide epidural anesthesia in the elderly patient.

Clinical Pearlss

Figure 56-4. The 24-h dose of epidural morphine required for effective analgesia after abdominal hysterectomy decreases with age (Reprinted, with permission, from Ready LB, Chadwick HS, Ross B, et al: Age predicts effective morphine dose after abdominal hysterectomy. Anesth Analg 1987;66:1215).

        Geriatric patients show an increased responsiveness to opioids. Epidural opioids are administered to surgical patients to provide prolonged postoperative analgesia. A reduction in the requirements of epidural morphine in older patients was reported. The cause is thought to be related to higher CSF concentrations²⁰ (Figure 56-4). Patientcontrolled epidural analgesia (PCEA) provides effective management of postoperative pain via the epidural route. It was suggested that the bolus dose and infusion rate of opioids be reduced up to 50% when administered to the elderly.

Spinal Anesthesia

The effect of age on the maximal height of spinal analgesia with isobaric solutions is marginal.^21,22 The complete, profound, long-lasting motor blockade and the increased duration of analgesia with glucose-free bupivacaine spinal anesthesia in elderly patients provide satisfactory conditions for orthopedic and vascular surgical procedures in the lower limbs. On the other hand, use of a hyperbaric solution increased the level of analgesia with age, extending some three to four segments higher in elderly patients than occurred in young adult patients^22,23 (Table 56-2). Both with glucose-free and hyperbaric bupivacaine solutions, the prolongation of action at the T12 dermatome allows more time for operations in the lower abdominal or inguinal region in older patients. In addition, a more rapid development of motor blockade was reported in older patients. Spinal anesthesia with hyperbaric bupivacaine is very suitable for lower abdominal and urologie procedures of intermediate duration in elderly patients. The reduction of the volume of CSF and the changes in the anatomic configuration of the lumbar and thoracic spine with advancing age may all contribute to the more extensive block using hyperbaric solutions in elderly patients.

        Intrathecal opioids are administered to surgical patients to provide prolonged postoperative analgesia. Respiratory depression is a concern in elderly patients receiving spinal opioids. A reduction in the requirements of epidural morphine in older patients was reported and thought to be related to higher CSF concentrations.²⁴ Spinal anesthesia with bupivacaine and fentanyl is well tolerated in nonpremedicated elderly patients.²⁵ Caution should be used when benzodiazepines are given as premedication and concomitantly in geriatric patients.

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.