Anesthesiology
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Noxious stimulation-induced sensitization of the central nervous system has been proposed as a key element in the development of subsequent protracted pain. Accordingly, the authors used the formalin model of pain to test the hypothesis that general anesthesia can produce preemptive analgesia and thereby interfere with noxious stimulation-induced central sensitization. ⋯ Nitrous oxide induces dose-dependent preemptive analgesia in this model that is reversed partially by naloxone, thus suggesting the involvement of endogenous opioids in this action. In contrast, halothane has no preemptive analgesic properties and even antagonizes the analgesic effect of nitrous oxide. Hence, the hypnotic potency of an anesthetic is a poor indication of its preemptive analgesic potential.
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Mivacurium's rapid onset and short duration of action in children suggests that intramuscular administration might treat laryngospasm and facilitate tracheal intubation without producing prolonged paralysis. Accordingly, the authors measured the neuromuscular effects of intramuscular mivacurium in anesthetized infants and children. ⋯ Although ventilatory depression preceded twitch depression, both occurred later with intramuscular mivacurium than would be expected after intravenous mivacurium or intramuscular succinylcholine. The authors speculate that the onset of intramuscular mivacurium is too slow to treat laryngospasm or to facilitate routine tracheal intubation in infants or children, despite administration of large doses.
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There are no clinical data regarding the ratios and concentrations in which morphine and bupivacaine should be combined, when given intrathecally, to improve analgesia while decreasing adverse effects. This study was undertaken to test the clinical efficacy of a constant infusion of 0.5 mg/ml morphine plus 4.75 mg/ml bupivacaine (morphine: bupivacaine approximately 1:10), given through open intrathecal catheters. ⋯ A constant intrathecal infusion with a morphine:bupivacaine ratio of approximately 1:10 and concentrations of morphine of 0.5 mg/ml and bupivacaine of 4.75 mg/ml may significantly improve the relief of refractory cancer pain with a certain risk of adverse effects (which should be balanced against pain by the patient) from the relatively high intrathecal bupivacaine doses and concentration.
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Opioids are thought to have equal analgesic effects when equivalent doses are used. However, sufentanil may achieve maximum effect while occupying fewer spinal opioid receptors (higher intrinsic efficacy). Therefore, sufentanil may be more effective than morphine when administered intraspinally in opioid-tolerant patients. ⋯ These results suggest that sufentanil can be used successfully in opioid-tolerant patients who do not experience adequate pain control in the early postoperative period despite a large dose of epidural morphine. Moreover, sufentanil should be considered an effective alternative therapy for postoperative pain control in chronic opioid users using high doses of oral opioids before surgical intervention.