Articles: anesthetics.
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Molecular pharmacology · Jan 1984
Membrane expansion and inhalation anesthetics. Mean excess volume hypothesis.
High-precision solution densimetry was used to determine volume parameters for the interaction of inhalation anesthetics with water, nonpolar solvent, and phospholipid vesicles. The precision of the densimeter is mainly limited by the constancy of the temperature during measurement. Therefore, temperature stability was maintained within +/- 0.0005 degrees and monitored by a microprocessor-controlled Thermistor thermometer with 0.0001 degrees resolution. ⋯ Because the mean excess volume of anesthetics dissolved in water is always negative and that incorporated into phospholipid suspension is positive, anesthetics expand the total volume of the model membrane system when translocated from water to the membrane. Anesthesia occurs when the mean excess volume of the total system exceeds a limiting value, and the bulk membrane size is irrelevant. Although the present result in no way disclaims alternative hypotheses, it demonstrates that the pressure reversal of anesthesia can be explained without assuming any specific receptors for these anesthetics.
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The problem of waste anesthetic gases must be addressed because of potential health hazards. However, solutions must be considered within a larger context than that of the operating room or dental suite. The impact of shifting wastes from the hospital into the atmosphere must be examined for both ecologic and ethical implications. ⋯ Are waste anesthetic gases an atmospheric pollutant with impact sufficient to cause concern? If not, do the economic considerations of recycling exhausted anesthetic and respiratory gases warrant implementation? Anesthesiologists need to consider these issues within the constraints of the environments in which they practice. The problem will exist as long as inhalation anesthesia is in use. Solution should not create new problems.
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Treatment with drugs and exposure to many environmental chemicals results in enzyme induction. However, the clinical significance of increased (or altered) metabolism of the inhaled anaesthetics appears to be trivial. Enzyme induction does not affect the conduct of inhalation anaesthesia. ⋯ Whether induction of halothane biotransformation and the production of reactive intermediates may lead to hepatoxicity is not yet settled. It is quite clear that induction, in the presence of hypoxia, leads to hepatic necrosis in rats. However, a similar relationship has not been established in surgical patients.
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Comparative Study
Differential peripheral nerve block by local anesthetics in the cat.
Controversy still surrounds the differential susceptibility of nerve fibers to local anesthetic conduction block. In order to help resolve this controversy, we developed an in vivo model of peripheral nerve blockade in the cat that closely reproduced the clinical state. Using this model, differential rate of nerve blockade of A-alpha, A-delta, and C fibers by 2-chloroprocaine, lidocaine, bupivacaine, and etidocaine was observed and quantitated. ⋯ Etidocaine blocked A-delta fibers first. A-alpha fibers always were blocked last. Of the four local anesthetics tested, 2-chloroprocaine produced the greatest differential rate of block of the nerve fibers, and etidocaine produced the least.