British medical bulletin
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Pain can either be 'nociceptor-mediated', produced as a consequence of the activation of high threshold nociceptors, or 'A-fibre mediated', resulting from the activation of low threshold A beta afferent fibres. Under normal circumstances nociceptor mediated pain only occurs in response to high intensity noxious stimuli. Following peripheral tissue injury the inflammatory reaction generates a complex set of chemical signals that alter the transduction properties of nociceptors such that they can be activated by low intensity stimuli, the phenomenon of peripheral sensitization. ⋯ This is the phenomenon of central sensitization. Because afferent inputs can provoke prolonged alterations within the central nervous system, optimal treatment of acute pain states should be directed both at abolishing peripheral sensitization and to preventing the establishment of central sensitization. The latter involves the strategy of pre-emptive analgesia.
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The clinical management of acute pain has been impeded by traditions and misconceptions which have resulted in suboptimal application to the patient of the currently available methods of pain control. The search for new drugs and exotic ways to deliver them has further obscured many of the basic principles which should guide management. Standard regimens fail because of the wide, unpredictable variability in pain intensity, patient characteristics, and pharmacological responses. ⋯ The delivery of opioid analgesics can be improved using patient controlled analgesia or spinal administration in some cases. Regional analgesia, often using simple techniques, can produce excellent pain relief. Overall management and staff education should be delegated to an acute pain service.
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Successful treatment of sympathetic pain is directed at the restoration of normal function. This can be achieved in the majority of cases with a combination of appropriate sympathetic or somatic nerve block, usually coupled with aggressive physiotherapy. ⋯ Other non-invasive techniques such as stimulation-produced analgesia and pharmacology, particularly the use of adrenergic blocking agents, hold some promise of future benefit. Here too, more effort should be made to carry out properly designed studies, as there is scepticism about the place of permanent or potentially destructive therapy in any painful condition.
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British medical bulletin · Jul 1991
ReviewOpioid-responsive and opioid-non-responsive pain in cancer.
Cancer pain in general responds in a predictable way to analgesic drugs and drug therapy is the mainstay of treatment, successfully controlling pain in 70-90% of patients. The two major problem areas are pain associated with nerve damage, and 'incident' (movement-related) bone pain. Nerve damage pain tends not to respond well to morphine or other opioids. ⋯ The patient may then experience excessive side-effects at rest, but still have pain on movement. Other examples of pain which may be resistant to treatment with opioid analgesics are bladder and rectal tenesmus, pancreatic pain, and pain associated with decubitus ulcers or other superficial ulcers subjected to pressure or shearing forces. Management of non-opioid-responsive pain may include a variety of treatments involving adjuvant analgesic drugs and non-drug measures.
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Neurogenic pain is defined as pain due to dysfunction of the peripheral or central nervous system, in the absence of nociceptor (nerve terminal) stimulation by trauma or disease. Other terms used to describe some (but not all) forms of neurogenic pain include neuropathic pain, deafferentation pain, and central pain; all these terms are subsumed into the wider expression 'neurogenic pain'. ⋯ This is undoubtedly proportionately greater than its incidence in chronic pain as a whole, and is a measure of its intractability and of the therapeutic dilemma which it presents. However, neurogenic pain syndromes are much commoner than is perhaps generally recognized: when all categories are taken into account, there are probably more than 550,000 cases in the UK population of 56 million at any one time, i.e. a prevalence of about 1%.