Anaesthesia
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Recent published data suggest that despite apparently satisfactory recovery from nondepolarising block (train-of-four ratios in excess of 0.90), even very small doses of additional relaxant may re-establish significant paralysis. We sought to verify this observation and quantify its magnitude. Twelve adult patients were studied under nitrous oxide-propofol-opioid anaesthesia and neuromuscular block was monitored electromyographically. ⋯ The control ED50 of mivacurium (calculated from the initial dose of mivacurium) averaged 43 micrograms.kg-1. When the same dose of drug was given at 95% recovery of the train-of-four ratio, the ED50 was reduced to 19 micrograms.kg-1 (p < 0.0001). Hence, there remains a considerable reduction in the neuromuscular margin of safety even at a train-of-four ratio of 0.95.
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Comparative Study
A practical evaluation of four human-powered portable airway aspirators.
The establishment of a clear airway is a vital part of basic life support and mechanical devices are available to assist the clearance of the upper airway during resuscitation. The performances of four human-powered devices, currently available in the United Kingdom, were compared with the relevant British Standard. The ease of use of the devices by 20 experienced and 20 novice resuscitators was assessed. ⋯ However, two devices ('Res-Q-Vac' and 'Ambu Maxi Suction Pump') were more user friendly. The incidence of airway contamination during resuscitation and the current recommended resuscitation protocols suggest that there is a need for increased emphasis on these airway adjuncts in life-support training. Wider access to basic life support equipment inside and outside hospital premises may improve resuscitation outcome.
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Malignant hyperthermia susceptibility is genetically heterogeneous. The ryanodine receptor gene on the long arm of chromosome 19 represents an important candidate gene but not all families with malignant hyperthermia demonstrate ryanodine receptor mutations or linkage to this region of 19q. Linkage to chromosome 17 in the region of the adult muscle sodium channel alpha subunit gene has been suggested in some families; others are not linked to either of these loci. ⋯ We have performed linkage analysis in a large family group with malignant hyperthermia in which the in vitro muscle contracture test had been carried out using the procedure standardised by the European Malignant Hyperthermia Group. None of the published ryanodine receptor gene mutations associated with malignant hyperthermia susceptibility were detected in affected individuals but linkage to intragenic ryanodine receptor markers strongly suggest that this gene is involved in malignant hyperthermia susceptibility in this family. This enabled accurate predictive testing by DNA analysis in 11 untested subjects at 50% risk.
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This study was undertaken to evaluate the effect of the levering laryngoscope on the view obtained at laryngoscopy. Two hundred and ten consecutive patients who required tracheal intubation were studied. The view at laryngoscopy with the levering laryngoscope blade in the neutral and elevated positions was recorded. ⋯ In patients where the view of the larynx was grade 1 or 2 with the blade in the neutral position, elevation of the levered tip often (23%) resulted in the view being impaired. This was not a clinical problem as the blade could simply be returned to the neutral position. The levering laryngoscope is a useful additional aid to laryngeal visualisation.
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The hypothesis that anaesthetic uptake during maintenance of anaesthesia is related to cardiac output was tested on 21 patients undergoing cardiac surgery. Using a computer-controlled closed breathing system, enflurane was administered to maintain an end-expired concentration of 1%. ⋯ A clear qualitative but not quantitative relationship was demonstrated. Changes in anaesthetic requirements at a constant end-expired concentration are a better guide to changes in cardiac output than changes in end-expired carbon dioxide with constant ventilation in patients undergoing cardiac surgery.