Pain
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Ketamine hydrochloride is a well known general anesthetic and short acting analgesic in use for almost 3 decades. The role of the NMDA receptor in the processing of nociceptive input has led naturally to renewed clinical interest in N-methyl-D-aspartate (NMDA) receptor antagonists such as ketamine. This paper reviews the use and efficacy of low-dose ketamine in the management of acute postoperative pain. ⋯ We conclude that ketamine may provide clinicians with a tool to improve postoperative pain management and to reduce opioid related adverse effects. The evidence suggests that low-dose ketamine may play an important role in postoperative pain management when used as an adjunct to local anesthetics, opioids, or other analgesic agents. Further research is required in the following areas: (a) dose-finding studies for ketamine as an adjunct to opioids and local anesthetics (b) efficacy and optimal route of administration (c) the role of S(+)-ketamine; (d) the influence of ketamine on long-term outcome such as chronic pain (e) long-term physical and chemical stability of mixtures containing ketamine (f) spinal toxicity of ketamine and (g) effects of low-dose ketamine on cognitive and memory functioning after surgery.
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This essay is an attempt to clarify the construct of unpleasantness in the context of the psychophysics of pain. The first critical point is that one aspect of unpleasantness is tightly coupled to stimulus intensity and is therefore a sensory discrimination. Pain has this quality, but so do other somatic sensations such as itch and dysesthesias that are not recognized as painful by most people. ⋯ I suggest that the sensory-discriminative/affective-motivational dichotomy has outlived its usefulness and is currently more of an impediment than a guide to neurobiological explanations of pain. In order to increase our understanding of pain we need psychophysical tools designed specifically to differentiate primary unpleasantness from both algosity and secondary unpleasantness. These tools can then be used to determine the neural mechanisms of pain.