Introduction and Definitions
Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or is defined in such terms as those set forth by the International Association for the Study of Pain (IASP).1,2 Inherent in the definition of pain is its multidimensional nature. There are three dimensions of pain, which are defined as the sensory discriminative, motivational affective, and cognitive evaluative.3 The sensory discriminative component of pain mediates the quality, intensity, duration, and location of the pain. The motivational affective component is concerned with the emotional aspects and the unpleasantness associated with pain. Lastly, the cognitive evaluative dimension of pain modulates both of the previous two dimensions and puts pain in the context of past experiences and current state of the individual. This chapter will discuss the basic science mechanisms of pain, the assessment of pain, and the management of wound-related pain. When possible, reviews, books, or book chapters are referenced to provide additional information for the reader. For a more in-depth review of the basic science mechanisms and an evidence-based approach for management of a variety of pain conditions, the reader is referred to "Pain Mechanisms and Management for the Physical Therapist."1
Spontaneous pain, or pain at rest, is very common and can be a substantial part of the pain associated with wounds. Referred pain is pain felt outside the area of injury and is not associated with a response to an applied stimulus. The most common example of referred pain is that of pain in the left shoulder and down the left arm during a heart attack (angina pain from cardiac ischemia). Pain can occur in response to externally applied stimuli and may be referred to as evoked incident pain. Hyperalgesia is an increased pain response to a normally noxious (painful) stimulus. When this increased pain response occurs at the site of injury, it is termed primary hyperalgesia. Hyperalgesia also may occur outside the site of injury and is called secondary hyperalgesia. (Fig. 22.1) Primary hyperalgesia is thought to reflect changes in the peripheral nervous system, whereas secondary hyperalgesia is thought to be mediated by changes in the central nervous system (more on secondary hyperalgesia will be covered below in the section Central Pain Pathways). Allodynia, on the other hand, is defined as pain in response to a normally innocuous (nonpainful) stimuli or activities.2 Allodynia is thought to be mediated by changes in the central nervous system where activation of a peripherally located non-nociceptor is perceived as painful. An example of allodynia is a painful response to gentle touching of the skin after wounding from a burn injury.
Primary and secondary hyperalgesia. Two burns were formed on the glabrous skin of the hand (A and D). Mechanical pain thresholds for pain were recorded at sites A, B, and C. Mechanical pain threshold decreased at all three of the ...