Anesthesiology
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d-Tubocurarine (dTc) was infused intravenously into 35 cats anesthetized with chloralose and urethane at a constant continuous rate to produce and maintain 90 per cent depression of twitch height of the anterior tibial muscle following supramaximal stimulation of the peroneal nerve. The mean infusion rates that produced 90 per cent depression were not significantly altered by respiratory acid-base changes. Metabolic alkalosis decreased (32.5 per cent) and metabolic acidosis increased (27.7 per cent) the required infusion rate of dTc. ⋯ However, during respiratory acidosis (pH 7.13, Paco2 66 torr) and metabolic alkalosis (pH 7.59, Paco2 36 torr) 20.0 and 18.0 mug/kg neostigmine, respectively, were needed to produce 50 per cent antagonism. Still larger doses of neostigmine (75 mug/kg) could not completely antagonize the block unless pH and Paco2 were returned to 7.30-7.50 and 35-45 torr, respectively. It is concluded that respiratory acidosis and metabolic alkalosis limit and oppose antagonism of dTc by neostigmine.
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Comparative Study
Effects of peridural block: V. Properties, circulatory effects, and blood levels of etidocaine and lidocaine.
Ten healthy, unpremedicated, male volunteers, aged 21-33 years, were given 20 ml 1 per cent etidocaine with 5 mug/ml epinephrine for peridural analgesia via a catheter placed L2. On a different occasion they were given 20 ml 2 per cent lidocaine with 5 mug/ml epinephrine in the same manner. Initial onset of sensory analgesia to pin prick was faster for etidocaine (7 min) than for lidocaine (9 min). ⋯ Mean maximum arterial concentrations of lidocaine were 2.22 plus or minus 0.09 mug/ml (plasma) and 1.85 plus or minus mug/ml (whold blood), achieved at 24 plus or minus 2 min. No sign of central toxicity was observed with either drug, although subjects receiving lidocaine tended to sleep, which was not the case with etidocaine. Hematologic screening, blood chemistries, and urinalyses performed 24 hours before and after each study showed no abnormality.
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Two important measures may be derived from patient responses to a range of anesthetic doses. The AD50, corresponding to MAC, estimates the median anesthetic concentration--that dose where half the patients are anesthetized and half are not. The AD95 approaches the theoretical "minimum" anesthetic concentration by estimating the dose that anesthetizes 95 per cent of a patient population. ⋯ Recomputed from available data , the AD50's of nine inhaled anesthetics proved to be numerically identical to their MAC values. The AD95's of nine inhaled anesthetics proved to be numerically identical to their MAC values. The AD95's were 5 to 40 per cent greater than the AD50's.)Key workd: Potency, anesthetic, MAC, AD50, AD95; Pharmacology, dose-response curves.)