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62: Geriatric Anesthesia

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CHAPTER 62 Geriatric Anesthesia

Gurdev S. Rai, MD

1 What is geriatric anesthesia and why is it important?

image Geriatric anesthesia is defined as providing anesthetic care for patients older than 65 years old.
image The geriatric population of the United States exceeds 35 million people, 12% of the total population. This population accounts for 33% of all surgical procedures performed in the United States.
image Geriatric patients consume 50% of the U.S. Federal Health Care Budget.
image Their population is expected to double by the year 2050.

2 What are the overriding characteristics and principles governing age-related physiologic changes as they relate to anesthesia in geriatrics?

Basal function of most organ systems is relatively unchanged by the aging process per se, but the functional reserve and ability to compensate for physiologic stresses is reduced. However, because of the diversity of this population, it is difficult to predict the extent of age-related physiologic changes and reduction in functional reserve for any particular individual.

3 Review age-related changes to the cardiovascular system

image Age-related wall thickening and stiffening of large elastic arteries reduces their compliance and increases afterload on the heart. These vascular changes can occur in the absence of atherosclerosis or hypertension and are independent predictors of mortality.
image Increased afterload (e.g., from hypertension) produces ventricular hypertrophy, leading to increases in wall stress, myocardial oxygen demand, and risk of ischemia.
image Diastolic dysfunction secondary to ventricular remodeling minimizes the ability to adjust stroke volume in response to changes in intravascular volume and tone.
image Stroke volume becomes more dependent on atrial preload for adequate end-diastolic volume.
image The atrium dilates as a result of impaired outflow secondary to ventricular remodeling, making the elderly more prone to atrial fibrillation. Fatty infiltration and fibrosis of myocardium manifests in conduction abnormalities and decreased heart rate variability.
image Down-regulation of β-adrenergic receptors magnifies the decreased ability of the heart to reach maximal cardiac output acutely in response to stress.

4 Describe age-related changes to the pulmonary system

image Restrictive pulmonary changes are noted as increased thoracic stiffness increases the work of breathing and decreases maximal minute ventilation.
image Closing capacity surpasses functional residual capacity by age 65 years, increasing the risk of atelectasis.
image Decreased cough reflex, ciliary clearance, and compromised swallowing mechanics increase risk of perioperative aspiration and pneumonia.
image There is a centrally mediated decrease in ventilatory response to hypoxia and hypercapnia.
image Exposure time to environmental, genetic, and social factors increases the prevalence of lung diseases and further exaggerates the changes noted previously.

5 Discuss age-related changes to the nervous system

image There is overall cerebral atrophy, decreased complexity of neuronal connections and decreased synthesis of neurotransmitters, increased fibrosis of peripheral sympathetic neurons, and impairment of cardiovascular reflexes.
image Decreased skeletal muscle innervation (and atrophy) results in decreased strength and fine motor control.
image There is increased sensitivity to all anesthetic agents.

6 How is baseline renal function impaired in the elderly?

There is progressive decrease in glomerular filtration rate (GFR) because of a decrease in renal blood flow and renal mass and diminishing tubular dysfunction, impairing sodium homeostasis and the ability to respond to acid loads. Under normal circumstances these have no real clinical implications other than subclinical hyponatremia. However, in the face of surgical stress, the failure to adapt to acute volume changes can lead to hemodynamic instability. Therefore meticulous attention needs to be paid to intraoperative fluid and electrolyte management in the elderly population.

7 How does serum creatinine change with aging?

Despite progressive decreases in GFR, because of an overall decrease in muscle mass in the elderly, serum creatinine should remain normal or decrease.

8 How do changes in renal function affect anesthetic management?

Decreases in GFR and renal blood flow lead to an increased risk for intraoperative fluid and electrolyte disturbances and an increased risk of acute renal failure. Intravascular volume must be replaced to maintain urine output at 0.5 ml/kg/hr or more. Moreover, many medications used intraoperatively and their metabolites that depend on renal clearance have prolonged elimination half-lives and longer durations of action. An example of these would be morphine and its metabolites, which, if not used with renal function in mind, can result in prolonged respiratory depression.

9 How is liver function affected by aging? What are some anesthetic implications?

image Liver mass, hepatic blood flow, and hepatic reserve decrease.
image Age-related loss of endoplasmic reticulum leads to decreased protein synthesis, including albumin. Thus the serum levels of protein-bound drugs increase.
image Because of the exceptional reserve of the liver, only in the presence of other comorbidities such as alcohol abuse and hepatitis are clinically relevant decreases in drug metabolism noted.

10 In what ways does body composition change with aging?

image Decreased basal metabolic rate leads to an overall increase in percentage of body fat.
image Muscle mass decreases with time, especially with inactivity.
image Total body water decreases by 20% to 30% with age, resulting in decreased total blood volume.

11 How do these changes in body composition affect anesthetic management?

image Increased body fat leads to an increased volume of distribution for lipid-soluble drugs. Thus elderly patients may have an extended elimination time and prolongation of effect.
image Loss of skeletal muscle leads to a decrease in maximal and resting oxygen consumption, a slightly lowered resting cardiac output, and diminished production of body heat (predisposing to hypothermia). Despite a smaller muscle mass, elderly patients are not more sensitive to muscle relaxants, probably because of fewer receptors at the neuromuscular junction.
image Decreased total body water leads to a smaller volume of distribution and higher-than-expected plasma concentrations of water-soluble drugs.
image Elderly patients may have a greater-than-anticipated response to drugs and thus appear to be more sensitive.

12 Why are these patients prone to hypothermia?

Elderly patients have a reduced basal metabolic rate, produce less body heat, and have diminished reflex cutaneous vasoconstriction to prevent heat loss. Aging is also associated with a decrease in β-adrenergic receptors, which are integral to temperature homeostasis.

13 What is the affect of aging on anesthetic requirements?

The minimum alveolar concentration for volatile anesthetics decreases 4% to 5% per decade after age 40. The alveolar concentration of a volatile anesthetic increases more rapidly because of decreased circulation time. The median effective dose (ED50) for intravenous agents decreases as well.

14 How are the pharmacokinetics and quality of spinal anesthesia affected by age?

Elderly patients have decreased blood flow to the subarachnoid space, resulting in slower absorption of anesthetic solutions. They also have a smaller volume of cerebrospinal fluid, the specific gravity of which tends to be higher than that of younger patients. This leads to a higher final concentration for a given dose and may alter the spread of the anesthetic. Elderly patients may have accentuated degrees of lumbar lordosis and thoracic kyphosis, increasing cephalad spread and pooling in the thoracic segments. Thus one might see higher levels of spinal anesthesia accompanied by faster onset of action and prolonged duration. Older patients also have a lower incidence of postdural puncture headaches when compared with younger patients.

15 Review the dynamics of epidural anesthesia change with age

Older patients require a smaller local anesthetic dose to achieve the same level of block when compared with younger patients. This may be the result of narrowing of the intervertebral spaces.

16 Do all elderly patients need extensive preoperative testing?

Preoperative testing should be tailored to the level of risk of planned surgery, underlying illnesses, and functional status. An electrocardiogram is recommended if the patient has had a recent episode of chest pain or ischemic equivalent, is at medium to high risk for cardiac complications during surgery, or is undergoing intermediate- or high-risk surgery. Appropriate laboratory testing should be determined by the patient’s prior medical history, his or her medications, and the scope of the planned procedure. This topic is discussed further in Chapter 17.

17 Is there a difference in outcome when performing regional vs. general anesthesia in the elderly?

Results of studies are mixed and depend on the outcome measured and the procedure. In repair of hip fractures, incidence of deep venous thrombosis, fatal pulmonary embolism, and 1 month mortality has been shown to be significantly reduced using regional anesthesia. On the other hand, other large studies of peripheral vascular surgeries have failed to consistently detect meaningful differences in outcome between elderly patients receiving epidural vs. general anesthetics. There is a theoretic benefit of improved graft patency with epidural anesthesia, but this has not been demonstrated consistently through clinical trials.

18 What are the most common postoperative complications in elderly patients?

Adverse drug reactions are three times more likely in the elderly than young patients. Postoperative cognitive dysfunction (POCD) and delirium are very common among the elderly.

KEY POINTS: Geriatric Anesthesia image

1. Implications of age-related changes on anesthetic management are profound, affecting almost every aspect of perioperative care.
2. Basal function of most organ systems is relatively unchanged by the aging process, but the functional reserve and ability to compensate for physiologic stress are reduced.
3. Not all elderly patients need an extensive preoperative workup; tailor it to their underlying illnesses and invasiveness of the surgery.
4. In general, anesthetic requirements are decreased in geriatric patients.
5. There is increased potential for a wide variety of postoperative complications in the elderly; POCD is arguably the most common.

19 What is postoperative cognitive dysfunction and what are its risk factors?

POCD is a disorder in thought processes, including memory, language comprehension, visuospatial abstraction, and attention. Risk factors include advanced age, lower educational level, alcohol use, a prior history of stroke, and Alzheimer’s disease. Polypharmacy and delirium during hospitalization are also predictive of POCD.

The complexity of testing and lack of a standardized diagnostic battery of tests have challenged our understanding of POCD.

20 What are the implications of postoperative cognitive dysfunction on patient mortality?

The occurrence of POCD is associated with increased mortality during the first year after surgery. A rapid decline in cognitive function with a persistent course (greater than 3 months) further increases mortality in these patients. This is attributed to possible underlying health issues in patients with POCD, decreased compliance after surgery, and a higher rate of depression.

21 What can anesthesiologists do to limit postoperative cognitive dysfunction in at-risk patients?

There are not many well-powered studies laying out a plan for anesthetic management. We do know that POCD is not associated with any particular anesthetic technique and that deeper levels of anesthesia seem to be protective. There is also evidence that patient familiarity with the perioperative experience can be helpful. Other studies have hinted that involving a geriatrician in the preoperative evaluation of elderly patients might decrease the incidence of POCD. The most appropriate management would limit the use of drugs already associated with delirium in the elderly. These include but are not limited to long-acting opiates, benzodiazepines, and anticholinergic medications. It would also be appropriate to continuously reevaluate the elderly patient’s list of medications with the purpose of eliminating unnecessary medications and considering undesirable synergistic effects.

22 Is age itself a predictor of perioperative mortality in the elderly?

Age itself has proven to be a poor predictor of mortality; more predictive risk factors include the following:

image Emergent abdominal or thoracic surgery
image A low preoperative albumin level (reflective of overall nutritional status)
image The number and severity of coexisting diseases
image POCD
image Lack of exercise tolerance and increased frailty

Websites image

American Society of Anesthesiologists’ Syllabus on Geriatric Anesthesia

http://www.asahq.org/clinical/geriatrics/syllabus.htm

American College of Cardiology/American Heart Association Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery

http://www.acc.org/clinical/guidelines/perio/dirIndex.htm

SUGGESTED READINGS

1. Bryson G.L., Wyand A. Evidence-based clinical update: general anesthesia and the risk of delirium and postoperative cognitive dysfunction. Can J Anesth. 2006;53:669-677.

2. Farag E., Chelune G.J. Is depth of anesthesia, as assessed by the bispectral index, related to postoperative cognitive dysfunction and recovery? Anesth Analg. 2006;103:633-640.

3. Monk T.G., Weldon B.C., Garvan C.W., et al. Predictors of cognitive dysfunction after major noncardiac surgery. Anesthesiology. 2008;108:18-30.

4. Silverstein J.H., et al. Geriatric anesthesiology, ed 2. New York: Springer, 2008.

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