British journal of anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Risk of aspiration with the laryngeal mask.
In order to assess if the use of the laryngeal mask airway is associated with an increased risk of gastric regurgitation during mechanical ventilation, we studied 50 patients allocated randomly to undergo anaesthesia with either artificial ventilation with isoflurane and nitrous oxide in oxygen and atracurium (group A) or spontaneous ventilation with isoflurane and nitrous oxide in oxygen (group B). In both groups a laryngeal mask airway was used. ⋯ In one patient in each group, there was staining of the oropharynx with blue dye at the end of surgery. In the patient in group A, dye was present in the trachea and bronchi.
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We have described the design and design considerations of the desflurane Tec 6 "vaporizer" and have tested its performance characteristics. The vaporizer differs from previous vaporizers designed for anaesthesia in that electromechanical rather than mechanical controls accommodate the different physical characteristics of desflurane. This design, while offering perhaps an increased risk of failure (owing to sophisticated electronic components and circuitry), on the other hand offers the decreased likelihood of accidental delivery of very large concentrations of liquid anaesthetic resulting from tilting or overfilling and alarms and warnings not previously incorporated into the design of anaesthetic vaporizers. The output characteristics of the vaporizer are as expected, based on the design: desflurane concentration output in oxygen has accuracy (+/- 15%) which is similar to that of the mechanical vaporizers; output decreases when nitrous oxide is added owing to the lower viscosity, but remains within 20% of the dial setting or 0.5% absolute.
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Comparative Study
The effects of sevoflurane are similar to those of isoflurane on the neuromuscular block produced by vecuronium.
We have examined the interactions of 1 MAC of isoflurane and sevoflurane (and 66% nitrous oxide in oxygen) with vecuronium, using the EMG response of the abductor digiti minimi to train-of-four (TOF) stimulation of the ulnar nerve. We constructed dose-response curves for vecuronium in 54 patients. ⋯ The rate of recovery of T4:T1 was significantly greater when both anaesthetics were discontinued. However, this rate was similar for both anaesthetics, suggesting that the mechanism of action of the two anaesthetics is similar.
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Comparative Study
Duration of spinal anaesthesia is determined by the partition coefficient of local anaesthetic.
We have compared the duration of motor block produced by four local anaesthetics administered into a chronically implanted subarachnoid catheter in rabbits. Each group (n = 6) received four different doses of amethocaine, bupivacaine, lignocaine or procaine, and the duration of the resulting motor block was assessed. Dose-response curves were plotted for each drug. ⋯ An inverse linear correlation (r = 0.995; P < 0.01) was observed between log D60 min and the log of the partition coefficient of the local anaesthetics. No correlation was found between the effect and degree of protein binding, pKa or molecular weight. These results suggest that, in spinal anaesthesia, the partition coefficient could be used as a predictor of the duration of anaesthetic action.
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We describe the successful use of the short-acting, non-depolarizing neuromuscular blocking agent, mivacurium, in a patient with myasthenia gravis taking pyridostigmine 120 mg four times daily. Increased sensitivity to mivacurium was demonstrated using train-of-four monitoring. ⋯ Residual block was antagonized without difficulty using neostigmine 2.5 mg. We discuss the relationship between plasma cholinesterase, acetylcholinesterase and anticholinesterase drugs.