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Managing pain in obese patients

D'Arcy, Yvonne MS, CRNP, CNS

doi: 10.1097/01.NPR.0000407601.90514.52
Feature: PAIN MANAGEMENT: Ce Connection

Obesity has become an epidemic in American healthcare. Comorbidities such as diabetes and cardiac disease increase the mortality and morbidity for these patients. Obesity-related pain conditions can limit the patient's efforts at increasing activity and limit quality of life. This article will offer information on these conditions and treatment options.

Yvonne D'Arcy is a pain management and palliative care nurse practitioner at Suburban Hospital-Johns Hopkins Medicine, in Bethesda, MD.

The author is a consultant for Ortho-McNeil, Pfizer, and Endo and on the speaker's bureau for Endo and Pfizer. The planners disclose no financial relationship pertaining to this article.



Obesity is a national health issue that affects every aspect of healthcare. Comorbidities, such as diabetes, hypertension, and dyslipidemia, contribute to the complexity of care required for effective treatment of obese patients and are commonly addressed by healthcare practitioners. However, pain-related comorbidities, such as diabetic neuropathy or low back pain related to an obese body structure, appear to receive less attention. This may be related to the need to address the significant issues of disease management, such as glycemic control and BP management, in the short period of time that the primary care provider has available for each patient. “Simple” pain issues may be overlooked while discussing more life-threatening health issues.

Nurse practitioners and other healthcare providers need to provide obese patients with a venue to discuss pain management issues. Information about the effects of obesity on pain and weight reduction strategies, coupled with pain management techniques, will help patients improve their health and pain relief.

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Prevalence of obesity

The prevalence of obesity is a global issue that is increasing dramatically. The World Health Organization (WHO) reports that more than 1 billion people worldwide are overweight; 300 million meet the criteria for obesity.1 By 2030, if current patterns persist, 58% of the world's population is expected to be obese or overweight.2 The two main contributing factors to obesity identified at the WHO regional meetings were diet and lack of exercise. Obesity has serious consequences. In 2002, the WHO identified the burden of noncommunicable diseases, such as cardiovascular disease, diabetes, cancers, and obesity-related conditions, as accounting for 60% of global deaths and 47% of the global burden of these diseases.1

Given the serious health repercussions of obesity, it appears inevitable that obesity-related pain has taken a back seat to the more serious consequences of obesity. However, pain management is a key factor for obese patients to become more active and attain a higher quality of life. Lifestyle changes alone may not reduce the pain of osteoarthritis or low back pain complicated by obesity. Unfortunately, some healthcare providers see the obese patient as someone who has created their own problem, one that weight loss would solve. The answer is not that simple. There are metabolic issues that need consideration when assessing the full picture of obesity-related pain.

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Factors for pain assessment

One way to categorize obese patients is by using body mass index (BMI). Classifications are as follows:3

  • Normal weight is classified by a BMI of 18.5 to 24.9
  • Overweight is classified by a BMI of 25.0 to 29.9
  • Obese Class I is classified by a BMI of 30.0 to 34.9
  • Obese Class II is classified by a BMI of 35 to 39.9
  • Obese Class III–morbid obesity–is classified by a BMI over 40

Using a BMI can help determine if the patient has an increased potential for developing a comorbid condition that will result in pain. For example, the higher the patient's weight and increased duration with obesity directly correlates with higher amounts of body fat causing increased insulin resistance, which can be a part of metabolic syndrome (MetS).3 MetS is a syndrome that includes the conditions of hypertension, central adiposity, elevated fasting blood glucose, and dyslipidemia with high triglycerides and low high-density lipoprotein cholesterol.3

When insulin resistance is present alongside MetS, negative effects on the patient's health are increased. MetS can cause higher rates of diabetes and cardiovascular disease, especially in women. There is also a positive correlation between MetS and increased systemic inflammation, which is fed by adipose tissue.4 Tumor necrosis factor, interleukin-6, and C-reactive protein are all factors secreted by adipose tissue that mediate insulin resistance and create a proinflammatory state that has been associated with increased joint inflammation and osteoarthritis.4

Increases in BMI can be directly linked to a greater incidence of pain-related conditions. Obesity has been cited as a contributor to the development of low back pain (possibly a result of increased load on spinal structures). Diabetes increases with the duration and degree of obesity, which can result in diabetic neuropathy in poorly controlled diabetes. There is also research support that indicates that obesity is an exacerbating factor for migraine headaches.5

Women diagnosed with osteoarthritis have a BMI that is 24% higher than average.6 In a study of 677 patients who had a total knee replacement and 547 patients who had a total hip replacement with at least one MetS risk factor, findings indicated the outcome of the surgeries was negatively affected by metabolic abnormalities.4 The two major factors that affected negative outcomes were obesity and hypertension.4

Because of obesity, women may also suffer from low self-esteem that can lead to depression. Since depression may be present comorbidly with chronic pain, these patients have an increased risk factor for both pain and depression.

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Obesity is a common comorbidity of fibromyalgia.7,8 Studies indicate that 32% to 50% of patients with fibromyalgia are obese; an additional 21% to 28% are overweight.9,10 In the general population, fibromyalgia affects about 3% to 5% of the U.S. population.7,8 It affects more women than men and is characterized by chronic widespread pain on both sides of the body with hyperalgesia in at least 11 of 18 specific points. In addition to the widespread pain, patients may also experience sleep disturbances, chronic fatigue, functional disability, mood disorder, “fibro fog” memory loss, headache, paresthesia, and irritable bowel disorder.7,8

In a study of 215 patients with fibromyalgia, 30% were overweight, with an additional 47% recognized as obese.The obese patients reported greater sensitivity to tender point palpation (especially in the lower body), decreased physical strength and lower body flexibility, and shorter sleep duration with greater restlessness while sleeping.8

Research has not clearly defined the cause and effect relationship between obesity and fibromyalgia. Animal studies suggest there is a link between greater levels of proinflammatory cytokines resulting in central sensitization.8 The list of mechanisms that might contribute to a link between fibromyalgia and obesity include impaired physical activity, cognitive and sleep disturbances, psychiatric comorbidity and depression, dysfunction of the thyroid gland, and impairment of the endogenous opioid system.7 The only demonstrated outcome was that obesity contributes to the continued presence of fibromyalgia and increases its severity.

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Low back pain

Findings indicate that if a patient is obese at age 23, there is a risk of low back pain within 10 years. As obese patients get older, the probability of developing low back pain increases.3 There have also been associations that show a BMI over 30 puts patients at greater risk for low back pain.11 Suspected mechanisms for the increased occurrence of low back pain in obese patients are mechanical stress on the intervertebral disks and indirect effects of atherosclerosis on decreasing blood flow to the lumbar spine.3

Many practitioners feel that weight loss is the solution to treating low back pain in these patients. There are two important issues to consider. Once low back pain is present, weight loss may not reverse the effect of mechanical load bearing, and not all weight loss strategies have the same result on low back pain. In two studies where morbidly obese patients had bariatric surgery, there was a significant decrease in low back pain after surgery.11 In a nonsurgical weight loss program, there was little evidence that demonstrated improvement in low back pain.11 Multidisciplinary programs that include exercise and weight loss as well also dietary and behavioral modification have a better outcome than treatment plans that are not as comprehensive.

It is important to note that no matter which type of treatment is selected to reduce low back pain, the ability of patients to adhere to the treatment requirements should be considered to achieve the best possible outcome for the patient. In low back pain, weight loss may have a positive effect and help to relieve the pain.

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Symptomatic osteoarthritis is the presence of radiographic findings of osteoarthritis in combination with symptoms attributable to osteoarthritis.12 Magnetic resonance imaging findings include cartilage lesion, osteophytes, bone marrow lesions, synovitis, effusion, and subchondral bone attrition.12 The two major risk factors for developing osteoarthritis are obesity and being female; knee injury is also a predisposition to developing knee osteoarthritis.

Even patients who were overweight but not morbidly obese had 2.2 times the risk for developing knee osteoarthritis when compared to their normal weight counterparts.12 In the United Kingdom, it is estimated that 69% of knee replacement surgeries in middle-age women are attributed to obesity.13

For the morbidly obese, knee osteoarthritis presents a bigger problem. If lifestyle changes and increased exercise cannot produce weight loss or favorable outcomes, total joint replacement is considered. If surgery is necessary, reconditioning after surgery can be complicated further by difficulty with mobility.

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Pain management

Treatment options for obese patients with pain include medications as well as non-pharmacologic modalities, such as acupuncture or yoga. When discussing options for controlling pain it is important to inform patients that a combination of treatments is more likely to produce optimum pain reduction.

Medications can be affected by the ratio of adipose tissue to lean body tissue. In the obese patient, there is a higher ratio of adipose tissue when compared to lean body tissue, which is thought to interfere with the protein binding of drugs allowing an increased concentration into the free plasma concentration. Although obesity increases the total volume of both lean and adipose tissue when compared to nonobese patients of the same age, height, and sex, this difference requires individualized prescriptions for obese patients to ensure that medications are dosed appropriately (see Physiologic factors that affect the utilization of medication in obese patients).14

For most obese patients in pain, opioids will be considered for pain management. Some are not candidates for nonsteroidal anti-inflammatory drugs due to impaired organ function, such as renal dysfunction, or comorbidities, such as diabetes or the potential for gastric bleeding.

Additional options for pain management in the obese patient can include not only medication management but the use of regional analgesia such as blocks and physical therapy programs geared to patients who need a less strenuous approach such as pool therapy where exercises are performed in warm swimming pools to decrease the stress on joints. Referrals to pain clinics, physical therapy programs designed for the obese patient, and physiatrists can help reduce pain and increase functionality. If the obese patient needs a surgical intervention, additional concerns will need to be addressed.

Sedation and the maintenance of a patent airway is always a concern when opioids are used for obese patients, especially in the postoperative time period when anesthetic agents have been used. However, reviews indicate that two factors, site of surgery (especially bariatric surgery), and coexisting sleep apnea have been cited as contributory to an increased risk of pulmonary complications in obese patients.15 Most obese patients can tolerate opioids in the usual doses, although they require close monitoring, especially for sedation and respiratory depression.

General recommendations for pain management after surgery for obese individuals include:15

  • The use of multimodal analgesia using regional and opioid sparing techniques
  • Avoidance of sedatives, especially when combined with opioids
  • Noninvasive ventilation with supplemental oxygen
  • Early mobilization and ambulation
  • Elevating the head of the bed to 30 degrees
  • A low threshold for pulse oximetry, which should be continuous also combined with end-tidal carbon dioxide monitoring for added safety
  • Arterial BP management
  • Placement in a nursing specialty area, such as ICU or stepdown unit, with continuous, postoperative monitoring until oxygen saturation is greater than 90% while asleep without supplemental oxygen

When obese patients use patient-controlled analgesia, the use of continuous infusion is contraindicated. Opioid requirements are not related to body surface, age, sex, or anesthetic regimen.15 Adding a nonopioid medication such as pregabalin (Lyrica), currently off-label use for acute pain, can decrease pain and provide an opioid-sparing effect.15,16 The use of other medications such as clonidine (Catapres), ketamine (Ketalar), and dexmedetomidine (Precedex) could be useful adjuvants for postoperative pain relief, but have significant contraindications and less research to support use at this time.16 The use of regional blocks with local anesthetic for adjunct pain relief is recommended, as well as epidural pain management for surgical pain. These techniques can reduce the need for opioids and can have a positive effect on the risk of respiratory depression. Obese patients will need less local anesthetic when administered as an epidural as compared to nonobese patients. This can be correlated with the decreased cerebrospinal fluid volumes in obese individuals.14

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Nonpharmacologic treatment

Less-invasive adjuvant pain relief modalities can also be considered. In one study, aromatherapy with lavender was shown to decrease morphine dosage needed for pain management in the postanesthesia unit, although more research is needed.15 Relaxation techniques such as music or relaxation tapes can provide a way to avoid medications through distraction. Reiki or therapeutic touch can also provide relaxation. In the outpatient setting, patients can participate in pool exercise therapy to lessen the burden on joints.

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It can be a challenge to provide effective pain management for obese patients; however, a multimodal pain management regimen that combines medications and complementary techniques can help increase pain relief. Recognizing that the patient may need to be in an area with continuous monitoring will help lessen the potential for adverse events in postoperative patients. Always remember that most obese patients are very familiar with the healthcare system and may have had less than positive experiences. Recognizing the patient's pain and working with the patient to help minimize the effects of the pain can lead to a more positive outcome.

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Physiologic factors that affect the utilization of medication in obese patients14

There are several physiologic factors that can affect the utilization of medication in the obese patient including the following:

  • A high prevalence of obstructive sleep apnea can preclude the combining of medications and require increased monitoring for sedation and respiratory changes if opioids are used. It is essential to use conservative dosing and educate the patient about medications and the need for monitoring when starting a medication. Patients should be instructed to report any adverse effects such as sedation to the healthcare provider. A return phone call to the patient within 24 hours to ascertain if there are any adverse effects can provide early warning of any difficulties. It is also wise to make sure the obese patient with obstructive sleep apnea is using continuous positive airway pressure (CPAP) as prescribed.
  • Changes in hepatic and renal function that can be affected by the fatty degeneration of the liver while renal clearance may be increased.
  • Creatinine clearance calculations will be inaccurate in patients with renal dysfunction, requiring an accurate measurement of creatinine clearance to dose medication appropriately.
  • Reductions in cardiac performance may reduce tissue perfusion (although only 5% of the cardiac function is directly affected by cardiac perfusion).
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