Anesthesiology
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Randomized Controlled Trial Clinical Trial
Propofol causes a dose-dependent decrease in the thermoregulatory threshold for vasoconstriction but has little effect on sweating.
Volatile anesthetics increase the core temperature required to trigger sweating and decrease the core temperature required to trigger vasoconstriction. However, little is known about the effects of intravenous anesthetics on thermoregulation. We therefore tested the hypothesis that propofol increases the sweating threshold and decreases the vasoconstriction threshold, thereby increasing the inter-threshold range (core temperatures not triggering autonomic thermoregulatory responses). The study was conducted using a new model in which thermal manipulations were restricted to insensate skin, and sensate skin temperature was controlled. ⋯ Like volatile anesthetics, propofol reduces the vasoconstriction threshold and increases the inter-threshold range. However, propofol differs in leaving the sweating threshold unchanged.
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Randomized Controlled Trial Clinical Trial
Deliberate mild intraoperative hypothermia for craniotomy.
Despite enthusiasm for the use of mild hypothermia during neurosurgical procedures, this therapy has not been evaluated systematically. This study examined the feasibility and safety of deliberate mild hypothermia and rewarming. ⋯ Although deliberate mild hypothermia is easily achieved intraoperatively, complete rewarming may be difficult to attain during craniotomy with current methods. In addition to the need for determining whether deliberate mild hypothermia confers cerebral protection in humans, the potential risks of the therapy need to be further characterized.
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Randomized Controlled Trial Clinical Trial
Effect of infusion rate on thiopental dose-response relationships. Assessment of a pharmacokinetic-pharmacodynamic model.
The rate of administration of an intravenous anesthetic induction agent is an important variable determining the total dose required to reach a given endpoint, such as loss of consciousness (LOC). The influence of infusion rate on the dose-response relationship has not been described rigorously. In this study we characterized the effect of different thiopental infusion rates on the times and doses required to reach a clinical (induction) endpoint. ⋯ In this study we quantified the relationship between the rate of thiopental administration and the resultant cumulative thiopental dose necessary to produce LOC. This study validated a novel pharmacokinetic-pharmacodynamic model based on a four-compartment pharmacokinetic model and infusion quantal dose-response data. Finally, we demonstrated that thiopental dose-response relationships are dependent on drug administration rate, and found that the ability to predict this dependence accurately is influenced by the pharmacokinetics, pharmacodynamics, and median effect-site concentration used to simulate the dose-response relationships.
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Randomized Controlled Trial Clinical Trial
Thermoregulatory thresholds during epidural and spinal anesthesia.
There are significant physiologic differences between spinal and epidural anesthesia. Consequently, these two types of regional anesthesia may influence thermoregulatory processing differently. Accordingly, in volunteers and in patients, we tested the null hypothesis that the core-temperature thresholds triggering thermoregulatory sweating, vasoconstriction, and shivering are similar during epidural and spinal anesthesia. ⋯ Comparable sweating, vasoconstriction, and shivering thresholds during epidural and spinal anesthesia suggest that thermoregulatory processing is similar during each type of regional anesthesia. However, thermoregulatory control was impaired during regional anesthesia, as indicated by the significantly enlarged inter-threshold and sweating-to-shivering ranges.
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Randomized Controlled Trial Clinical Trial
The electroencephalogram does not predict depth of isoflurane anesthesia.
The power spectrum of the electroencephalogram (EEG) may be analyzed to provide quantitative measures of EEG activity (e.g., spectral edge, which defines the highest EEG frequency at which significant activity is found). The current study tested the hypothesis that spectral edge and similar measures distinguish different functional depths of anesthesia in humans. ⋯ We conclude that our EEG measures do not predict depth of anesthesia as defined by the response to surgical incision, the response to verbal command or the development of memory.