Anesthesiology
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Randomized Controlled Trial Clinical Trial
Intravenous or epidural clonidine for intra- and postoperative analgesia.
Intravenous and epidural clonidine both produce postoperative analgesia. Several experimental reports demonstrate a spinal site of action for the analgesic effects of this alpha 2-adrenoceptor agonist. Therefore, the authors evaluated the clinical analgesic benefits of using clonidine, both intra- and postoperatively, by the epidural or the intravenous route. ⋯ Epidural clonidine reduces the intra- and early postoperative analgesic requirements when compared with the same dose given by the intravenous route. The side effects were similar with the two routes of administration.
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Comparative Study
The threshold for thermoregulatory vasoconstriction during nitrous oxide/isoflurane anesthesia is lower in elderly than in young patients.
Thermoregulatory vasoconstriction minimizes further core hypothermia during anesthesia. Elderly patients become more hypothermic during surgery than do younger patients, and take longer to rewarm postoperatively. These data indicate that perianesthetic thermoregulatory responses may be especially impaired in the elderly. Accordingly, the authors tested the hypothesis that the thermoregulatory threshold for vasoconstriction during nitrous oxide/isoflurane anesthesia is reduced more in elderly than in young patients. ⋯ These data indicate that thermoregulatory responses in the elderly are initiated at temperatures approximately 1.2 degrees C less than that in younger patients. Thus, it is likely that elderly surgical patients become more hypothermic than do younger patients, at least in part, because they fail to trigger protective thermoregulatory responses.
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Although computer-controlled infusion (CCI) of alfentanil has been shown to be effective intraoperatively, this technique has not been validated for postoperative use. Therefore, the authors examined the efficacy of this technique in providing postoperative pain relief. The study comprised both a validation of published pharmacokinetic data sets and the definition of the minimum effective analgesic concentrations after major orthopedic surgery. ⋯ Computer-controlled infusion of alfentanil provides adequate postoperative analgesia. The study demonstrated that pharmacokinetic data sets that are useful for intraoperative CCI of alfentanil are equally valid in the postoperative phase. Although required plasma concentrations of alfentanil are reasonably stable in time, interindividual variations are large, necessitating individual titration.
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Randomized Controlled Trial Comparative Study Clinical Trial
Desflurane and isoflurane have similar effects on cerebral blood flow in patients with intracranial mass lesions.
Before desflurane is advocated for patients undergoing neurosurgical procedures, it is necessary to determine the effect of desflurane on cerebral blood flow (CBF). In this study, CBF values are compared between desflurane and isoflurane at two doses. In addition, CBF reactivity to CO2 and the effect of prolonged exposure were compared between the two agents. ⋯ Desflurane and isoflurane are similar in terms of absolute CBF, the response to increasing doses, and the preservation of CO2 reactivity.
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Randomized Controlled Trial Clinical Trial
Clonidine comparably decreases the thermoregulatory thresholds for vasoconstriction and shivering in humans.
Clonidine stops postoperative shivering, but its underlying mechanism of action is unknown. Clonidine may impair central control of thermoregulation or act on peripheral receptors. Accordingly, the authors tested the hypothesis that clonidine reduces both the vasoconstriction and shivering thresholds, a pattern consistent with central thermoregulatory impairment. ⋯ Seven healthy volunteers participated in the study. Thermoregulatory vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients; values exceeding 4 degrees C were considered to be significant vasoconstriction. Systemic oxygen consumption (VO2) was measured with a canopy system. In addition, shivering was qualitatively evaluated using a simple scale, graduated from 0 (no shivering) to 2 (intense shivering). The tympanic membrane temperatures triggering significant vasoconstriction and grade 1 shivering were considered to be the thresholds for the two thermoregulatory responses. Measurements were performed after a 10-min steady state period and during cooling by central venous infusion of Ringer's lactate solution at 4 degrees C. Each subject was evaluated at two sessions, separated by at least 48 h. They were randomly and blindly assigned to received either an intravenous bolus of 75 micrograms clonidine or a placebo before cooling. When the shivering score equaled 2, 75 micrograms clonidine was injected intravenously, and repeated if necessary, to completely stop shivering.