Cath Lab Digest

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Index: Ostomy Wound Manage. 2008;54(11):38-47.

Wounds cause pain but the consequences of wound pain remain largely unknown. Studies from other disciplines have shown that pain can contribute to the long-term physiological and emotional consequences of the pain experience, setting the stage for the phenomenon referred to as “learned pain.” Providing ways to help patients avoid learning pain — ie, modulating pain anticipation/expectation, peripheral nerve blocks, pretreatment analgesics, biophysical technologies, modification of patient and provider behavior, judicious choice of dressings, and behavioral therapies — has been found to play a significant role in decreased physical and emotional discomfort and improved outcomes. Existing evidence on pain suggests that wound pain most likely consists of a combination of local, systemic, and learned phenomena retained by the patient as long-term “pain memories” as well as acute reaction to stimuli. Until the consequences of wound pain are fully appreciated, healthcare providers should consider application of research findings from other disciplines to reduce pain and prevent the learning and development of pain memories.

KEYWORDS: wound pain, review, learned pain, pain memories, wound pain prevention, modulation

     Wounds cause pain and caring for a wound contributes to the long-term physiological and emotional consequences of having pain. The International Association for the Study of Pain (ISAP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.”¹ Pain also has been described as a response to an unpleasant stimulation of individual nociceptors in the periphery when perturbated at a given area of the body and transmitted to higher centers in the brain.² The World Union of Wound Healing Societies (WUWHS)3 defines wound-related pain as “a noxious symptom or unpleasant experience directly related to an open skin ulcer.” The ISAP definition comes closest to considering the impact of pain on the whole person by including both the physiological and psychological components of emotional experience.

     Robust findings reported in the literature substantiate the significant impact of brain neural networks on the pain experience and include: 1) the nervous system is able to reorganize and learn responses and behaviors that are retained as “pain memories”^4,5; 2) pain expectations are learned from past experience and affect pain perception6,7; 3) pain expectations profoundly influence pain-related brain activation, need for analgesic medication, wound care treatment adherence, and healing outcomes^8-10; and 4) clinician and patient actions during therapy affect brain activity and wound healing, providing an opportunity to influence patient outcomes. This article presents an overview of a compendium of information on pain found in the literature — human studies comprising randomized controlled trials, case studies, and qualitative studies, as well as basic science studies on animals — to enhance understanding, and ultimately practice, regarding the pain experience as it relates to wound care.

Brain Function Related to Pain

     Useful technologies. Brain functional activity can be observed using neuroimaging technology such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), high-resolution electroencelphalography (EEG), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS).