Anesthesiology
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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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Randomized Controlled Trial Clinical Trial
Propofol reduces perioperative remifentanil requirements in a synergistic manner: response surface modeling of perioperative remifentanil-propofol interactions.
Remifentanil is often combined with propofol for induction and maintenance of total intravenous anesthesia. The authors studied the effect of propofol on remifentanil requirements for suppression of responses to clinically relevant stimuli and evaluated this in relation to previously published data on propofol and alfentanil. ⋯ Propofol reduces remifentanil requirements for suppression of responses to laryngoscopy, intubation, and intraabdominal surgical stimulation in a synergistic manner. In addition, remifentanil decreases propofol concentrations associated with the return of consciousness in a synergistic manner.
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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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Propofol is a common sedative hypnotic for the induction and maintenance of anesthesia. Clinicians typically moderate the dose of propofol or choose a different sedative hypnotic in the setting of severe intravascular volume depletion. Previous work has established that hemorrhagic shock influences both the pharmacokinetics and pharmacodynamics of propofol in the rat. To investigate this further, the authors studied the influence of hemorrhagic shock on the pharmacology of propofol in a swine isobaric hemorrhage model. ⋯ Hemorrhagic shock altered the pharmacokinetics and pharmacodynamics of propofol. Changes in intercompartmental clearances and an increase in the potency of propofol suggest that less propofol would be required to achieve a desired drug effect during hemorrhagic shock.