Pain Management in the Geriatric Population

Abstract

Pain is a highly prevalent and clinically important problem in the elderly. Unfortunately, due to difficulties in assessing pain in geriatric patients, the complexities of multiple comorbidities, and the high prevalence of polypharmacy, many practitioners are reluctant to treat pain aggressively in this unique patient population. Safe and effective treatment therefore, requires a working knowledge of the physiologic changes associated with aging, the challenges of accurately assessing pain, the unique effects of common therapeutic agents upon the elderly as well as the importance of adjunctive therapies. The following review is intended to provide the practitioner with practical knowledge for safer and more effective treatment of pain.

Introduction

Appropriate management of chronic and acute pain in the geriatric population creates several unique challenges, as it is an increasingly common and often undertreated condition. In patients over 60-years old, the prevalence of pain was more than two times that reported for patients under 60-years old.¹ Other studies have indicated that 60% of independent and 80% of long-term care geriatric patients report substantial daily pain² clearly making it one of the most common symptoms reported by elderly patients.³ Inadequate treatment of pain is associated with adverse outcomes including depression, anxiety, sleep disturbances and mood changes.⁴ Appropriate recognition and treatment of pain becomes important, because in developed countries, the fastest growing portions of the population are individuals who are greater than 75 years of age.⁵ This group is increasingly active with expectations of having a functional lifestyle with increased quality of life.³ Appropriate pain management is essential in achieving these expectations.

Pain is often undertreated in the geriatric population for a number of reasons. First, many practitioners and patients hold the misconception that pain is an expected and natural consequence of aging.¹ Second, many elderly patients have physical impairments, such as visual or hearing loss, or cognitive impairment which include confusion, memory loss, or dementia that interfere with clear communication.³ Third, concerns of either the practitioner or patient regarding the side effects of opioids, including respiratory depression, addiction⁶ and falls, often create a barrier to indicated therapies. Fourth, because of the multitude of medications typically used by the elderly in treating a variety of other medical conditions, there is concern about drug-drug interactions and polypharmacy.⁵ Finally, the patient often underreports pain because of the fear that it may represent impending death, loss of autonomy or require further treatment or testing.¹ Fortunately, health care providers can better understand the unique aspects of pain control in the geriatric population and greatly improve quality of life.

Some non-pharmacological treatment options include physical therapy, osteopathic manipulation, massage therapy, TENS units, acupuncture, biofeedback, cognitive behavioral therapy and psychotherapy.

Geriatric Physiology and Pharmacology

The appropriate pain management regimen starts with a clear understanding of the physiological changes associated with aging and their effect on pharmacology. Aging affects the absorption, distribution, metabolism and clearance of medications.⁴ Advanced age is associated with increased body fat and a reduction in total body water.³ These changes increase the volume of distribution for a lipophilic and decrease it for a hydrophilic medication, thus altering the medication’s onset and effective dose. Protein binding is also frequently altered in the geriatric population, resulting in increased bioavailability in some medications.⁶

Both hepatic and renal function are decreased in the elderly resulting in a decrease in the ability to metabolize and eliminate medications,³ placing the patient at increased risk of toxic side effects of pain medications.⁴ Hepatic function decreases by 1% per year after the age of 50,³ hepatic mass and blood flow are reduced and the cytochrome P450 metabolic pathway is less effective with increasing age.⁶ While the ability to metabolize drugs is generally decreased with age, the clinical result with regard to metabolic function remains highly individualized.⁶ Renal function decreases with age starting at age 30 with a decrease in glomerular filtration rate of 10 ml/min per decade.⁷ Due to the loss of muscle mass with age, the patient’s creatinine will also decrease³ resulting in a “normal” blood chemistry value this may mask the fact that the patient has some renal impairment. Unfortunately, many medications are eliminated by the kidneys and renal impairment can lead to a prolonged half-life.³ Of particular concern is the potential accumulation of pharmacologically active metabolites that also rely on renal elimination.

Central and peripheral nervous system changes are also associated with increasing age. While the amount of perceived pain is the same for both older and younger patients, the overall opioid requirements to control that pain is decreased with age.⁴ Neural transmission is altered along Aδ and C type pain carrying fibers¹ due to a decrease in density of both of myelinated and unmyelinated fibers.³ Despite these changes, there is little evidence that the process of nociception is altered due to age.⁵ By appreciating these differences, with careful monitoring and the slow adjustment to a single medication, geriatric patients can be effectively and safely treated with many pain medications despite a narrower therapeutic window.

Categorization and Assessment of Pain

Most of the chronic pain experienced in the elderly can be broadly categorized as cancer related pain and non-cancer pain. Cancer pain carries with it many unique aspects and is beyond the scope of this review. The most common etiologies for non-cancer pain in the elderly are arthritis (osteoarthritis and rheumatoid) and postherpetic neuralgia (PHN).³ Assessment of pain is essential in order to effectively recognize and treat pain. Self-reporting of pain is considered to be the most accurate way to measure the presence of pain and its intensity.¹ In circumstances where communication is impaired because of sensory, motor or cognitive dysfunction, pain tools and scales have been shown to be an effective means of measuring pain¹ so long as they are explained clearly and used consistently.

Opioids

The use of opioids for treatment in the elderly has increased within the past few years due to adverse gastrointestinal and cardiovascular complications associated with NSAIDS.⁸ The World Health Organization has advocated the use of opioids as part of three-step ladder in treating pain starting with simple analgesics like acetaminophen, and if pain is uncontrolled adding weak opioids (for example codeine) and finally if needed strong opioids, such as morphine.⁵ Opioids are recognized to greatly aid non-cancer chronic pain as well, but tend to be underutilized in the elderly population.³ A commonly held misconception is that avoiding opiates or using very low doses will help prevent the development of delirium in the elderly. One study showed that undertreating pain actually resulted in increasing rates of delirium in geriatric patients.⁹ Opioids can and should be used for geriatric patients but often require initially reduced doses (usually 50% less) when compared to younger patients.⁵ Multiple studies have demonstrated that opiate requirements decline with age,⁶ and that slow and incremental titration of the opioid is typically required to find the optimal level of drug administration. Clearly defined end goals need to be established prior to initiating treatment.⁴

Opioids act by binding presynaptic opioid receptors, which prevents release of the neurotransmitter substance P via membrane hyperpolarization, thereby preventing impulse propagation. Three subtypes of opioid receptors are found in varying locations: μ, κ and δ. Stimulation of differing receptors accounts for the varying clinical effects of opioids. Opioids useful in the treatment of pain are almost exclusively receptor agonists. Stimulation of the μ receptor produces analgesia, euphoria, miosis, bradycardia, hypothermia, respiratory depression, physical dependence, constipation and urinary retention. The κ and δ receptors also cause analgesia and a mixture of the unwanted effects listed above, plus dysphoria, sedation and diuresis. Opioids do not have a ceiling effect like acetaminophen and NSAIDS. Thus, if enough agonist is administered, analgesia will occur, though untoward effects may occur first and prevent further administration. The individual response to any given dose is highly variable and must be carefully tailored, particularly in the elderly and opioid naïve. Through receptor up-regulation, tolerance to opioids develops after repeated doses, meaning higher doses will be required to achieve the same efficacy. This occurs for both analgesic properties as well as most adverse effects save two, miosis and constipation, which will persist for the duration of opioid therapy.

With regard to the incidence of the adverse effects listed above, the most commonly reported among patients treated with opioids are constipation, nausea, dizziness and somnolence, all occurring in 21–30% of patients regardless of age.¹² Patients greater than 65 years of age are more likely to report constipation, fatigue and anorexia when compared to a younger cohort.¹² These findings highlight the importance of concomitant use of stool softeners and anti-nausea medications.

A recent meta-analysis suggests that analgesic efficacy is independent of age and provide significant pain reductions in older (≥65) and younger (<65) patients alike. Significant treatment effects in favor of opioid therapy for patients aged 65 and older were also reported for physical functioning, sleep and quality of life.¹²

Though abuse and misuse of opioids are certainly a growing problem in the United States, practitioners must be careful not to extrapolate those findings uniformly to all populations. Patients older than 60 are far less likely to exhibit behaviors most consistent with opioid abuse or misuse such as seeking prescriptions from multiple providers, forging prescriptions and claims of lost or stolen prescriptions.¹²

Acetaminophen and NSAIDS

Acetaminophen represents front line therapy for treatment of pain in the geriatric population. Acetaminophen is thought to selectively inhibit prostaglandin in the central nervous system.¹⁰ Although it is an effective antipyretic, it is devoid of anti-inflammatory effect. Unlike opioids, it does have a ceiling effect, meaning increasing doses will not yield increasing efficacy. Even in elderly patients, if the daily dose of acetaminophen is limited to 4 grams there is no evidence of liver failure or hepatic dysfunction.⁴ It is important for patients to examine all over the counter medications since many common formulations contain acetaminophen.

Since inflammation plays an important role in the nociceptive pathway, non-steroidal anti-inflammatory drugs (NSAIDS) are an important part of the multimodal approach to analgesia. Pain itself can also reciprocally fuel the inflammatory state, so-called neurogenic inflammation. Neurogenic inflammation can produce the same physiologic effects as direct tissue injury. When tissues are disrupted, some of the phospholipid bilayer of the membrane is converted to arachadonic acid. The cyclooxygenase enzyme then converts arachadonic acid into prostaglandin, necessary for transduction of noxious stimuli to the nociceptor as well as neurosensitization of painful stimuli and subsequent hyperalgesia. The cyclooxygenase enzyme has two isoforms, COX-1 and COX-2, with very different physiologic effects. Aspirin and most NSAIDS nonselectively block both isoforms, producing analgesia as well as potential adverse effects including coagulopathy, gastric ulceration and nephropathy. The hope that selective COX-2 inhibitors would produce analgesia without unwanted effects has not been supported by clinical data, and several of these compounds have been removed from use due to increased incidence of myocardial infarcts and cerebrovascular accidents.

Geriatric patients are at a higher risk of complications from NSAIDS including: renal failure, gastropathy, and cardiovascular disease.⁴ Gastroprotective agents, such as proton pump inhibitors (PPI), may help reduce some of these risks for the elderly,¹¹ however the other risk factors remain unmodified. Renal function, which normally declines after 30 years of age, is potentially decreased further with the use of NSAIDS, increasing the risk of renal impairment in the elderly.⁷ Prostaglandins needed to maintain glomerular filtration rate and renal blood flow are inhibited by NSAIDS leading to renal dysfunction.⁷

Other Pharmacologic Agents

Successful treatment of pain while limiting side effects often depends upon a multimodal approach. In addition to traditional therapies outlined above, there are several others that deserve mention. When pain syndromes become chronic, there is often an element of depression. Conversely, preexisting depression can greatly increase the perception of pain. Antidepressants, therefore, can be very useful in decreasing pain. Tricyclic antidepressants (TCA) and selective serotonin reuptake inhibitors (SSRI) are often prescribed. One large retrospective study in the elderly found amitriptyline and dosulepin (both TCA’s) to have the lowest rates of serious side effects studied such as mortality, stroke, falls, seizure and hyponatremia.¹³ However, another TCA, trazodone, was found to have some of the highest rates of complication, as were drugs from other classes such as venlafaxine and mirtazapine.¹³ For all drugs studied, complications tended to occur in the first 28 days of therapy and the first 28 days following discontinuation.¹³

In the case of neuropathic pain, TCA’s are useful as well as gabapentin and pregabalin. The choice between the two is usually made based on tolerability rather than efficacy.¹⁴ If the pain is localized, topical lidocaine and capsaicin may also be of benefit. Serotonin-noradrenaline reuptake inhibitors such as duloxetine and venlafaxine are considered second line agents.¹⁴

Non-Pharmacological Treatment Options

Considering the prevalence and importance of pharmacological adverse effects in the elderly, practitioners should always consider the myriad other treatment modalities available. Although not a comprehensive list, some of the more commonly used are physical therapy, osteopathic manipulation, massage therapy, TENS units, acupuncture, biofeedback, cognitive behavioral therapy and psychotherapy. All have been used safely in the geriatric population and are effective ways to both decrease pain and improve quality of life. The success of these is dependent on both the etiology of pain as well as the individual patient’s own capabilities.

Conclusion

Although pain becomes increasingly prevalent with age, it is not a normal part of the aging process. Pain can and does introduce a serious compromise to the quality of life of geriatric patients and in many cases, limits independence or ends it altogether. There are important barriers to overcome with regard to safe and effective treatment of pain such as proper assessment, multiple comorbid conditions, altered physiology and polypharmacy. Practitioners can help to achieve improved pain control through an understanding of these challenges, appropriate use of treatment modalities and using a multidisciplinary approach to treatment.

Biography

Robert Borsheski, DO, (left), MSMA member since 2013, is Director of Acute Pain Services, and Assistant Professor of Anesthesiology, Department of Anesthesiology and Perioperative Medicine. Quinn L. Johnson, MD, (right), MSMA member since 2007, is Interim Chairman, Department of Anesthesiology and Perioperative Medicine, and Director of Anesthesiology of the Missouri Orthopedic Institute. Both are at the University of Missouri.

Contact: johnsonql@health.missouri.edu