Anesthesia and analgesia
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Anesthesia and analgesia · Jul 1982
Pharmacokinetics of inhalation anesthetics: a three-compartment linear model.
The evolution of mathematical models of the uptake of the inhaled anesthetic agents has produced increasingly complex models in which researchers have attempted to incorporate more and more data on the effects of anesthetics on the processes of respiration, circulation, and metabolism. One result of this evolution has been to limit the application of these models due to the large amount of data required by the model and the need for a large digital computer to generate a solution. ⋯ Only a programmable hand calculator is needed for the solution. Due to the simplicity of this model, compared with previously described models, it should prove useful in understanding the kinetics of gas uptake by the body.
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Anesthesia and analgesia · Jul 1982
Comparative StudyDifferential sensitivity of fast and slow fibers in mammalian nerve. III. Effect of etidocaine and bupivacaine on fast/slow fibers.
Etidocaine and bupivacaine are long acting local anesthetics with contrasting effects on motor and sensory function. The effect of these drugs on fast-conducting (large, motor) and slow-conducting nerve fibers (small, pain) in the isolated rabbit vagus nerve was examined. Both drugs had an equivalent effect on slow fibers. ⋯ During this long latency of effect by bupivacaine on fast fibers, only the slow fibers were blocked. This period of differential effect on fast and slow fibers is believed to be the explanation for the early effect of bupivacaine on pain fibers followed by a later block of motor function. This difference is believed to be due to the lower lipid solubility solubility and greater ionization of bupivacaine, which impedes diffusion across the permeability barriers present in fast-conducting A fiber.
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Anesthesia and analgesia · Jul 1982
Comparative StudyDifferential sensitivity of fast and slow fibers in mammalian nerve. II. Margin of safety for nerve transmission.
In a previous study it was found that concentrations of local anesthetics required to block large, fast-conducting nerve fibers were lower than those required to block small, slow-conducting fibers. The present study was instituted to evaluate the margin of safety for transmission in large versus small nerve fibers, the margin of safety being defined as the ratio between the magnitude of the action potential and the magnitude of the critical membrane potential. The effect of reducing the sodium-activating current, which reduces the magnitude of the action potential by sodium deficient solutions and tetrodotoxin application to the desheathed rabbit vagus nerve trunk (in vitro), was examined. ⋯ In all instances, the margin of safety for transmission was greater in small, slow fibers than in large, fast fibers. The variations seen in nerve response to tetrodotoxin application are explained by the presence of nerve fiber diffusion barriers; the large fibers show more diffusion protection than the small fibers. Onset, duration, and intensity of differential nerve blockade by drugs reflect a balance between diffusion barriers and axon membrane sensitivity.
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Anesthesia and analgesia · Jul 1982
Oxygen transfer from mother to fetus during cesarean section under epidural anesthesia.
The correlation between maternal PaO2 levels and umbilical vein (UV) and umbilical artery (UA)PO2 levels was studied in 40 healthy patients undergoing elective cesarean sections under lumbar epidural anesthesia. Patients were divided into four equal groups. Each group inhaled oxygen at a FIO2 of 0.21, 0.47, 0.74 (in nitrogen), or 1.0. ⋯ Maternal arterial, UV, and UA base excess values in the hyperoxic groups were significantly higher than in the normoxic groups. There was no difference in 1- or 5-minute Apgar scores between the normoxic and hyperoxic groups. It is concluded that maternal hyperoxia improves fetal oxygen stores and acid-base status during cesarean section under epidural anesthesia.