British journal of anaesthesia
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The spinal cord is the first relay site in the transmission of nociceptive information from the periphery to the brain. Sensory signals are transmitted from the periphery by primary afferent fibres into the dorsal horn of the spinal cord, where these afferents synapse with intrinsic spinal dorsal horn neurones. Spinal projection neurones then convey this information to higher centres in the brain, where non-noxious and noxious signals can be perceived. ⋯ After nerve injury or conditions of inflammation, shifts can occur in these excitatory and inhibitory mechanisms which modulate spinal excitability, often resulting in the heightened response of dorsal neurones to incoming afferent signals, and increased output to the brain, a phenomenon known as central sensitization. In this review, we consider the ways in which spinal cord activity may be altered in chronic pain states. In addition, we discuss the spinal mechanisms which are targeted by current analgesics used in the management of chronic pain.
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Older adults with persistent pain are not simply a chronologically older version of younger pain patients. Pain-related disability in older adults may be driven by pain 'homeostenosis', that is, diminished ability to effectively respond to the stress of persistent pain. Some of the comorbidities of ageing that can contribute to pain homeostenosis include cognitive and physical impairments, increased sensitivity to suprathreshold pain stimuli, medical and psychological comorbidities, altered pharmacokinetics and pharmacodynamics, and social isolation. ⋯ Specifically, we discuss age-related changes in the brain (both normal and pathological) and in pain physiology; changes in experience and expression of pain that occur with dementia and contribute to pain homeostenosis; and unique aspects of age and pain-associated psychological function and their contribution to disability. We also present data demonstrating changes in brain morphology and neuropsychological performance that accompany persistent non-malignant pain in older adults and the treatment implications of these brain changes. Finally, preliminary data are presented on the efficacy of mindfulness meditation, a treatment that has been examined explicitly in older adults and targets optimizing brain function and descending inhibition.
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Significant advances in the assessment and management of acute pain in children have been made, and are supported by an increase in the availability and accessibility of evidence-based data. However, methodological and practical issues in the design and performance of clinical paediatric trials limit the quantity, and may influence the quality, of current data, which lags behind that available for adult practice. Collaborations within research networks, which incorporate both preclinical and clinical studies, may increase the feasibility and specificity of future trials. ⋯ Chronic pain in children has a negative impact on quality of life, resulting in social and emotional consequences for both the child and the family. Despite age-related differences in many chronic pain conditions, such as neuropathic pain, management in children is often empirically based on data from studies in adults. There is a major need for further clinical research, training of health-care providers, and increased resources, to improve management and outcomes for children with chronic pain.
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Valid and reliable assessment of pain is essential for both clinical trials and effective pain management. The nature of pain makes objective measurement impossible. Acute pain can be reliably assessed, both at rest (important for comfort) and during movement (important for function and risk of postoperative complications), with one-dimensional tools such as numeric rating scales or visual analogue scales. Both these are more powerful in detecting changes in pain intensity than a verbal categorical rating scale. In acute pain trials, assessment of baseline pain must ensure sufficient pain intensity for the trial to detect meaningful treatment effects. Chronic pain assessment and its impact on physical, emotional, and social functions require multidimensional qualitative tools and health-related quality of life instruments. Several disease- and patient-specific functional scales are useful, such as the Western Ontario and MacMaster Universities for osteoarthritis, and several neuropathic pain screening tools. The Initiative on ⋯ Measurement, and Pain Assessment in Clinical Trials recommendations for outcome measurements of chronic pain trials are also useful for routine assessment. Cancer pain assessment is complicated by a number of other bodily and mental symptoms such as fatigue and depression, all affecting quality of life. It is noteworthy that quality of life reported by chronic pain patients can be as much affected as that of terminal cancer patients. Any assessment of pain must take into account other factors, such as cognitive impairment or dementia, and assessment tools validated in the specific patient groups being studied.