British journal of anaesthesia
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Comparative Study Clinical Trial Controlled Clinical Trial
Evaluation of the toxicity of local anaesthetic agents in man.
Etidocaine given by intravenous infusion has been compared, using a double-blind technique, with bupivacaine and lignocaine in respect of toxic symptoms and signs. The degree of toxicity is affected considerably by the rate of drug infusion. At 10 mg/min subjects could tolerate twice the dose of etidocaine as bupivacaine. ⋯ Lignocaine at 20 mg/min was better tolerated than etidocaine. Venous plasma concentration during these experiments showed a more rapid decrease in the case of etidocaine compared with bupivacaine, but the concentrations were unhelpful in predicting the toxic effects. Similarly electroencephalography revealed no abnormalities in spite of marked subjective and objective signs of toxicity.
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The change in end-tidal position (ETP) after suxamethonium-induced paralysis was measured in 15 children during routine general anaesthesia. In all patients the onset of muscle paralysis was associated with an increase in lung volume from ETP. This increase may be the result of paralysis of the expiratory muscles which are active during anaesthesia.
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Seven Alsatian dogs were anaesthetized with thiopentone, paralysed with pancuronium, and ventilated with 1% halothane in a mixture of air and oxygen in such a way as to maintain Paco2 at 40 mm Hg and Pao2 at 150 mm Hg. From various respiratory and circulatory measurementts the following variables were determined: physiologicaldeadspace, cardiac output, venous admixture, respiratory compliance and resistance, and oxygen and carbondioxide exchcnage. After a controlseries of measurements at a ventilator frequency of was doubled to 50/min and adjustments to tidal volume and inspired oxygen concentration made to maintain constancy of blood gas tensions. ⋯ Mean results showed that physiological deadspace changed relatively little with frequency so that the deadspace:tidal volume ratio increased significantly on changing to 50/min (by 24%) and decreased significantly on changing to 6/min (by 46%). Changes of cardiac output and venous admixture were either not significant or on the borderline of significance and the 95% confidence limits of these changes were within +14%, --12% for cardiac outpur and within plus or minus1.4% of cardiac output for venous admixture. Tt is concluded that, provided Paco2 and Pa02 and mean air way pressure are kept constant, the frequency of ventilation is not important, even over a wide range of values.
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Profiles on the progress of spinal extradural anaesthesia were made in 246 patients using various concentrations of lignocaine, bupivacaine and etidocaine. The advance of analgesia through the different dermatomes showed a consistent and orderly spread on the upper lumbar and thoracic segments. ⋯ This failure was abolished with the use of etidocaine 1.5%. The presence of a delay or failure at the level of L5-S2 is probably related to the larger diameter of these nerve roots as ascertained from measurements in 11 cadavers.
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Letter Case Reports
Dangerous fault in disposable connector for orotracheal tube.