Anesthesiology
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Comparative Study
Irreversible conduction block in isolated nerve by high concentrations of local anesthetics.
Delivery of large doses of local anesthetics for spinal anesthesia by repeated injections or continuous infusion could expose the cauda equina to concentrations of drug that may be neurotoxic per se. We studied this possible neurotoxic effect by assessing recovery from conduction blockade of desheathed peripheral nerves after exposure to some of the local anesthetic solutions commonly used for spinal anesthesia. ⋯ Solutions of 5% lidocaine and 0.5% tetracaine that have been associated with clinical cases of cauda equina syndrome after continuous spinal anesthesia caused irreversible conduction block in desheathed amphibian nerve. Whether these in vitro actions also occur in mammalian nerves in vivo is an important, clinically relevant question now under investigation in our laboratory.
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Comparative Study
Ephedrine remains the vasopressor of choice for treatment of hypotension during ritodrine infusion and epidural anesthesia.
Historically, ephedrine has been the vasopressor of choice for treatment of most cases of hypotension in obstetric patients. However, the choice of vasopressor in the parturient receiving a beta-adrenergic agent for tocolysis has not been evaluated extensively. The current study evaluated whether ephedrine or phenylephrine better restores uterine blood flow and fetal oxygenation during ritodrine infusion and epidural anesthesia-induced hypotension in gravid ewes. ⋯ Although ephedrine and phenylephrine provided similar restoration of maternal mean arterial pressure, ephedrine was superior to phenylephrine in restoring uterine blood flow during ritodrine infusion and epidural anesthesia-induced hypotension in gravid ewes. Also, ephedrine, but not phenylephrine, significantly improved fetal oxygenation, when compared to normal saline--control.
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Comparative Study Clinical Trial Controlled Clinical Trial
Effects of pressure-controlled with different I:E ratios versus volume-controlled ventilation on respiratory mechanics, gas exchange, and hemodynamics in patients with adult respiratory distress syndrome.
Pressure-controlled (PCV) and pressure-controlled inverse ratio ventilation (PCIRV) have been proposed instead of volume-controlled conventional ratio ventilation (VC) with positive end-expiratory pressure (PEEP) for patients with adult respiratory distress syndrome (ARDS). The advantages advocated with the use of PCIRV are to decrease airway pressures and to improve gas exchange. However, most studies did not compare PCIRV and VC while keeping both the level of ventilation and end-expiratory alveolar pressure (total-PEEP) constant. ⋯ In this prospective controlled study, no short-term beneficial effect of PCV or PCIRV could be demonstrated over conventional VC with PEEP in patients with ARDS.
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Randomized Controlled Trial Clinical Trial
Surgical stimulation induces changes in brain electrical activity during isoflurane/nitrous oxide anesthesia. A topographic electroencephalographic analysis.
The aim of this study was to investigate topographic changes in electroencephalographic (EEG) power and frequency induced by abdominal surgery during anesthesia with 0.6% or 1.2% isoflurane in 66% nitrous oxide. ⋯ The current data demonstrate graded EEG responses induced by abdominal surgery during anesthesia with 0.6% or 1.2% isoflurane in 66% nitrous oxide. Spatial heterogeneities in absolute spectral power densities were reflected by color changes in the EEG maps. The topographic EEG analysis indicates that these changes were most dominant at frontal areas. The increases in delta and decreases in alpha activities may be related to intraoperative "paradoxical" electrophysiologic arousal phenomena.
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Comparative Study
Preoperative methionine loading enhances restoration of the cobalamin-dependent enzyme methionine synthase after nitrous oxide anesthesia.
Prolonged exposure to nitrous oxide causes adverse effects mimicking those of cobalamin deficiency. This is explained by irreversible oxidation of cobalamin bound to the enzyme methionine synthase. The inactivation of methionine synthase by nitrous oxide in cultured human fibroblasts is decreased at high concentrations of methionine in culture medium. ⋯ Our data suggest that short time exposure to nitrous oxide selectively impairs the function of the cobalamin-dependent methionine synthase. Furthermore, preoperative administration of methionine should be considered as a means to counteract adverse effects of nitrous oxide.