Anesthesiology
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Anesthetic preconditioning (APC) is protective for several aspects of cardiac function and structure, including left ventricular pressure, coronary flow, and infarction. APC may be protective, however, only if the duration of ischemia is within a certain, as yet undefined range. Brief ischemia causes minimal injury, and APC would be expected to provide little benefit. Conversely, very prolonged ischemia would ultimately cause serious injury with or without APC. Previous investigations used a constant ischemic time as the independent variable to assess ischemia-induced changes in dependent functional and structural variables. The purpose of the study was to define the critical limits of efficacy of APC by varying ischemic time. ⋯ Although APC protects against vascular dysfunction and dysrhythmias after prolonged ischemia, protection against contractile dysfunction and infarction in this model is restricted to a range of ischemia durations of 25-40 min. These results suggest that APC may be effective in a subset of patients who have cardiac ischemia of intermediate duration.
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Randomized Controlled Trial Comparative Study Clinical Trial
Laryngeal resistance before and after minor surgery: endotracheal tube versus Laryngeal Mask Airway.
The placement of an endotracheal tube (ETT) may promote laryngeal swelling, which is an important cause of upper airway obstruction after extubation. The authors hypothesized that laryngeal swelling after ETT placement increases laryngeal resistance and tested that hypothesis by comparing postoperative laryngeal patency between patients with ETT placement and those with a Laryngeal Mask Airway trade mark (LMA). ⋯ Postoperative laryngeal resistance increases at least in part because of laryngeal swelling in patients with ETT placement, whereas alteration of laryngeal neural control mechanisms has been also indicated. The use of the LMA trade mark has an advantage over ETT placement in order to avoid postoperative laryngeal swelling.
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Clinical Trial
Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study.
Current techniques of brachial plexus block are "blind," and nerve localization can be frustrating and time consuming. Previous studies on ultrasound-assisted brachial plexus blocks are mostly performed with scanning probes of 10 MHz or less. The authors tested the usefulness of a state-of-the-art, high-resolution ultrasound probe (up to 12 MHz) in identifying the brachial plexus in five locations of the upper extremity and in guiding needle advancement to target before nerve stimulation. ⋯ These preliminary data show that the high-resolution L12-L5 probe provides good quality brachial plexus ultrasound images in the superficial locations i.e., the interscalene, supraclavicular, axillary, and midhumeral regions. The needle technique described here for ultrasound-assisted nerve localization provides real-time guidance and is potentially valuable for brachial plexus blocks.
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To simulate the time course of drug effect, it is sometimes necessary to combine the pharmacodynamic parameters from an integrated pharmacodynamic-pharmacodynamic study (e.g., volumes, clearances, k(e0) [the effect site equilibration rate constant], C(50) [the steady state plasma concentration associated with 50% maximum effect], and the Hill coefficient) with pharmacokinetic parameters from a different study (e.g., a study examining a different age group or sampling over longer periods of time). Pharmacokinetic-pharmacodynamic parameters form an interlocked vector that describes the relationship between input (dose) and output (effect). Unintended consequences may result if individual elements of this vector (e.g., k(e0)) are combined with pharmacokinetic parameters from a different study. The authors propose an alternative methodology to rationally combine the results of separate pharmacokinetic and pharmacodynamic studies, based on t(peak), the time of peak effect after bolus injection. ⋯ T(peak) is a useful pharmacodynamic parameter and can be used to link separate pharmacokinetic and pharmacodynamic studies. This addresses a common difficulty in clinical pharmacology simulation and control problems, where there is usually a wide choice of pharmacokinetic models but only one or two published pharmacokinetic-pharmacodynamic models. The results will be immediately applicable to target-controlled anesthetic infusion systems, where linkage of separate pharmacokinetic and pharmacodynamic parameters into a single model is inherent in several target-controlled infusion designs.
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Randomized Controlled Trial Clinical Trial
Pharmacokinetics of midazolam in neonates undergoing extracorporeal membrane oxygenation.
Although the pharmacokinetics of midazolam in critically ill children has been described, there are no such reports in extracorporeal membrane oxygenation. ⋯ These results reveal significantly increased volume of distribution and plasma half-life in neonates receiving extracorporeal membrane oxygenation. Altered kinetics may reflect sequestration of midazolam by components of the extracorporeal membrane oxygenation circuit.