Chapter 21: Pain Management

INTRODUCTION

DEFINING PAIN AND EDUCATING THE PATIENT

The International Association for the Study of Pain defines pain as an “unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Acute pain is the most common symptom that brings a patient to see a physician, and it is frequently the first sign of an ongoing pathologic process. Chronic pain, defined as pain lasting longer than 3 mo or a greater duration than expected, often has an unclear etiology that includes tissue injury and psychosocial factors. Whenever possible, inform the patient beforehand about the nature and the degree of pain to be expected during a hospital stay. Hospitalized patients, especially those with acute-on-chronic pain, should be made aware that his or her pain might not completely go away with treatment. Rather, the goal of pain management should be to achieve improved pain control to allow adequate function for recovery and performance of daily activities.

CLASSIFICATION OF PAIN

Nociceptive Pain

Pain due to stimulation of pain receptors, i.e., nociceptors. Nociceptive pain can be further characterized as somatic or visceral pain. Somatic pain is sharp, constant, well-localized, and is caused by injury to skin, subcutaneous tissue, muscle, blood vessels, or bones. Examples include incisional pain, bone fractures, phlebitis, and osteoarthritis. Visceral pain originates from nociceptors within the internal organs (viscera), and is poorly localized, crampy, and intermittent in frequency. Some examples are intestinal colic, bladder spasm, gastroesophageal reflux, urolithiasis, and angina.

First-line treatment for nociceptive pain includes nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen. When these medications fail to relieve symptoms, opioids may be considered. While NSAIDs are best at treating inflammatory pain exacerbated by movement, e.g., osteoarthritic joint pain, opioids are useful for treating pain at rest.

Neuropathic Pain

Pain resulting from damage of the nervous system. Neuropathic pain is typically described as “shooting” or “burning,” is poorly localized, and frequently occurs spontaneously. In addition, the pain can be accompanied by abnormal sensations (dysesthesias), including an exaggerated response to a painful stimulus (hyperalgesia) or the sensation of pain due to a nonpainful stimulus (allodynia). Sympathetic nerve stimulation may further exacerbate neuropathic pain. Examples include radiculopathy, postherpetic neuralgia, diabetic polyneuropathy, phantom limb pain, and nerve compression.

Neuropathic pain is best treated with anticonvulsants (e.g., gabapentin, pregabalin), antidepressants (e.g., duloxetine, amitriptyline, nortriptyline), or ...