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LEARNING OBJECTIVES
Upon completion of the chapter, the reader will be able to:
Identify characteristics of the types of pain: nociceptive, inflammatory, neuropathic, and nociplastic.
Explain the mechanisms involved in pain transmission.
Select an appropriate method of pain assessment.
Recommend an appropriate choice of analgesic, dose, and monitoring plan for a patient based on type and severity of pain and other patient-specific parameters.
Perform calculations involving equianalgesic doses, conversion of one opioid to another, rescue doses, and conversion to a continuous infusion.
Educate patients and caregivers about effective pain management, dealing with chronic pain, and the use of nonpharmacologic measures.
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Pain is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”1 
Pain is an unpleasant subjective experience that is the net effect of a complex interaction of the ascending and descending neurons involving biochemical, physiologic, and psychological processes. Pain can affect all areas of a person’s life including sleep, thought, emotion, and activities of daily living. There are no reliable objective markers for pain; thus, the patient is the only person who can describe the intensity and quality of their pain.
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EPIDEMIOLOGY AND ETIOLOGY
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Most people experience pain at some time in their lives, and pain is a symptom of a variety of diseases. Thus, identifying the exact prevalence of pain is a difficult task. Prevalence rates for a variety of different types of pain have been described (Table 35–1). Patients 65 years and older bear a significant burden of pain. The prevalence of pain in people older than 60 years is twice that in those younger than 60 years.2 Studies suggest that 25% to 50% of community-dwelling elderly suffer pain. Pain is quite common among nursing home residents. It is estimated that 45% to 80% of nursing home patients and 25% of those with daily pain received neither analgesic medication nor nonpharmacologic treatment for their pain, contributing to functional impairment and a decreased quality of life.2
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The financial impact of pain is considered to be significant. The total cost of pain in the United States has been estimated at $560 to $635 billion annually; about half of this cost is due to direct costs of health care while the other half is due to lost productivity.3