Anesthesiology
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Subsidiary atrial pacemakers assume control after sinoatrial (SA) node excision, and anesthetic-catecholamine interactions can produce severe bradycardia during isoflurane anesthesia. We hypothesized that epinephrine enhances atrial, atrioventricular junctional, and ventricular dysrhythmias after SA node excisions in dogs and that inhalation anesthetics would facilitate such dysrhythmias. ⋯ In dogs with excised SA nodes, anesthetic-catecholamine interaction facilitates ventricular escape, His bundle dysrhythmias, and premature ventricular beats. In addition, halothane and enflurane, more than isoflurane, facilitate ectopic ventricular tachydysrhythmias with epinephrine. Compared to intact dogs, dogs with excised SA nodes may be more susceptible to epinephrine anesthetic dysrhythmias. If findings can be extrapolated to humans, intrinsic SA node dysfunction may facilitate severe cardiac dysrhythmias with inhalation anesthetics and catecholamines.
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Minimum alveolar concentration (MAC) is decreased in pregnancy, but it is not known how quickly after delivery MAC returns to normal. We measured the MAC of isoflurane in a group of women undergoing elective tubal ligation after delivery. ⋯ The MAC of isoflurane was reduced in women 24-36 h postpartum and gradually increased to normal values by 72 h postpartum.
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Randomized Controlled Trial Comparative Study Clinical Trial
Clinical effects and maternal and fetal plasma concentrations of epidural ropivacaine versus bupivacaine for cesarean section.
Ropivacaine is a new amide local anesthetic structurally similar to bupivacaine and mepivacaine. Previous studies showed that ropivacaine has a similar clinical effect as bupivacaine with regard to sensory anesthesia and slightly less motor blockade than bupivacaine. Ropivacaine appears to be less cardiotoxic and arrhythmogenic than bupivacaine. The clinical and pharmacokinetic effects of 0.5% ropivacaine (5 mg/ml) versus 0.5% bupivacaine (5 mg/ml) when used epidurally for elective cesarean section were investigated. ⋯ Ropivacaine, 0.5%, epidurally provided satisfactory and similar sensory anesthesia compared to 0.5% bupivacaine for elective cesarean section. The Cmax was similar for both drugs, although the terminal half-life of ropivacaine was significantly shorter, and the blood concentrations of free ropivacaine were significantly greater than that for bupivacaine. These values were less than concentrations shown to be toxic in animals.
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Randomized Controlled Trial Clinical Trial
Pharmacokinetic model selection for target controlled infusions of propofol. Assessment of three parameter sets.
Computer-assisted target controlled infusions (TCI) result in prediction errors that are influenced by pharmacokinetic variability among and within patients. It is uncertain whether the selection of a propofol pharmacokinetic parameter set significantly influences drug concentrations and clinical acceptability. ⋯ Although it may be preferable to administer propofol TCI by using a locally derived parameter set, it is acceptable to use a model from elsewhere. The Marsh and Tackley models produced equally good performance and are appropriate for propofol TCI within the range of 3-6 micrograms/ml. The Dyck model was less accurate at maintaining anesthetic concentrations, possibly because it was derived from low concentrations. Concentrations in blood, the most sensitive indicators of performance, demonstrated differences among the parameter sets. Clinically, TCI worked well, and by clinical criteria, the choice of pharmacokinetic model did not appear to make a difference.
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Randomized Controlled Trial Clinical Trial
Oral clonidine prolongs lidocaine spinal anesthesia in human volunteers.
Premedication with oral clonidine may improve the quality and duration of lidocaine spinal anesthesia, but this effect has not been examined in a quantitative fashion. ⋯ Premedication with oral clonidine prolonged sensory and motor block from lidocaine spinal anesthesia. The exact mechanism whereby oral clonidine prolongs spinal anesthesia remains to be determined.