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efforts, this monograph has two primary objectives: 1) to provide practical knowledge that will enhance the reader’s understanding and management of pain and 2) to introduce some strategies to improve pain management (e.g., CPGs, standards), as further explored in monograph 2. Due to the breadth and complexity of the subject matter, a comprehensive discussion of all aspects of pain assessment and management is beyond the scope of this monograph. The scope and potential limitations of this monograph are as follows: ■ The neurological and psychological mechanisms that underlie pain are complex, and knowledge of mechanisms is limited. The discussion of pathophysiology in this monograph emphasizes practical knowledge that will facilitate diagnosis and/or the selection of appropriate interventions. ■ Controversy exists over how both pain and analgesics should be classified. This monograph reviews only a few of the many classification systems. ■ Various factors (e.g., insufficient funding for studies, lack of good diagnostic codes) limit the availability of current, reliable epidemiological data related to pain. ■ A host of factors, including the setting, characteristics of the pain, and patient factors (e.g., age, medical condition, language and cognitive abilities) influence pain National Pharmaceutical Council 3 Section I: Background and Significance a The Agency for Health Care Policy and Research is now the Agency for Healthcare Research and Quality. b These JCAHO standards first appeared in the 2000-2001 JCAHO standards manual and apply to ambulatory care, behavioral health, managed behavioral health, health care networks, home care, hospitals, long-term care organizations, and pharmacies. assessment. This monograph provides an overview of pain assessment, but primarily focuses on the initial assessment. ■ Many strategies exist to manage various types of pain. This monograph reviews pharmacologic and nonpharmacologic treatments for pain, with greater emphasis on the former. Specific information about the treatment of certain conditions is limited to some common and treatable types of pain. Coverage of treatment issues relevant to special populations (e.g., children, the elderly) is limited. ■ The discussion of pharmacologic treatments emphasizes: 1) the major classes of drugs used for pain management; 2) examples and salient features of these drugs; and 3) some means of ensuring the safe, strategic, and effective use of these agents. However, this information is only an overview. The reader should consult CPGs for specific guidance in managing patients. ■ Due to the large volume of associated literature, a review of the mechanisms, assessment, and management of pain associated with some conditions (e.g., cancer) is beyond the scope of this monograph. This monograph focuses on the pathophysiology, epidemiology, assessment, and treatment of acute pain and chronic noncancer pain (CNCP). B. D EFINITIONS AND M ECHANISMS O F PAIN This section of the monograph explores mechanisms that underlie the perception of pain. It also reviews a pain classification system based on underlying pathophysiology. The goal is to provide practical information that will facilitate pain assessment and management. A questionand-answer format is used to provide information about the following: ■ The definition of pain ■ The process by which noxious stimuli generate neural signals and the transmission of these signals to higher centers (nociception) ■ The role of inflammatory mediators, neurotransmitters, and neuropeptides in these processes (i.e., targets of many pharmacologic therapies) ■ Definitions and causes of some clinical pain states ■ Underlying mechanisms and characteristics of somatic pain, visceral pain, and neuropathic pain. 1. What Is Pain? In 1968, McCaffery defined pain as “whatever the experiencing person says it is, existing whenever s/he says it does”. 18 This definition emphasizes that pain is a subjective experience with no objective measures. It also stresses that the patient, not clinician, is the authority on the pain and that his or her self-report is the most reliable indicator of pain.13 In 1979, the International Association for the Study of Pain (IASP) introduced the most widely used definition of pain. The IASP defined pain as an “unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.’’19 This definition emphasizes that pain is a complex experience that includes multiple dimensions. 2. How Does Injury Lead to Pain? Nociception refers to the process by which information about tissue damage is conveyed to the central nervous system (CNS). Exactly how this information is ultimately perceived as painful is unclear. In addition, there can be pain without nociception (e.g., phantom limb pain) and nociception without pain. But classic descriptions of pain typically include four processes:20-23 ■ Transduction: the conversion of the energy from a noxious thermal, mechanical, or chemical stimulus into electrical energy (nerve impulses) by sensory receptors called nociceptors ■ Transmission: the transmission of these neural signals from the site of transduction (periphery) to the spinal cord and brain ■ Perception: the appreciation of signals arriving in higher structures as pain ■ Modulation: descending inhibitory
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