British journal of anaesthesia
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Comparative Study
Static v. dynamic tests in the in vitro diagnosis of malignant hyperthermia susceptibility.
In vitro contracture tests, in which muscle specimens are exposed to halothane or caffeine are, at present, the only generally accepted screening methods for the diagnosis of susceptibility to malignant hyperthermia (MHS). Static tests (performed with the muscle held at constant length) are used more commonly although, in addition, some MH investigation units use dynamic tests, in which the length of the specimen is varied. ⋯ The dynamic halothane test was more sensitive in discriminating between MHS and MH negative (MHN) individuals than the static halothane test. However, the dynamic caffeine test was less sensitive at discriminating between MHS and MHN individuals, and nothing is to be gained by including it in the investigation.
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An artificial patient capable of spontaneous and artificial ventilation has been used for bench testing of the Ohmeda CPU-1. This ventilator has an extensive capacity for interaction with the spontaneous breathing of the patient, and provides a wide variety of operating modes. These include spontaneous breathing with or without continuous positive pressure, volume-cycled and pressure-cycled artificial ventilation, with or without positive end-expiratory pressure or synchronization. ⋯ The synchronization permits adaptation of the ventilator to spontaneous respiration according to a wide range of harmonics. In any mode, artificial ventilation is initiated if spontaneous respiration is inadequate. The mandatory minute volume mode is based on a complicated program of a cautious nature which reacts instantly to inadequate spontaneous breathing, but is slow to discontinue artificial ventilation.
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Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient, a circulating pump and feedback controllers for system volume and anaesthetic concentration. ⋯ Stability was maintained with +/- 50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal halothane concentration and system volume to provide a rapid and optimized induction of anaesthesia.
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Male Fischer 344 rats were exposed to halothane, enflurane or isoflurane vapour 20 p.p.m., or air, for up to 30 weeks. None of the anaesthetic agents led to hepatocellular necrosis. ⋯ Urinary fluoride excretion was increased during exposure to either enflurane or isoflurane. Using this increase as an index of anaesthetic biotransformation, we found that the extent of biotransformation of isoflurane was only slightly lower than that of enflurane.
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Comparative Study
Recovery of spontaneous breathing following neuromuscular blockade with atracurium.
Atracurium 0.3 mg kg-1 was given to two groups of patients to compare the recovery of spontaneous breathing with that of peripheral neuromuscular function. Anaesthesia was maintained in one group (n = 6) with an infusion of etomidate (mean flow rate 24 micrograms kg-1 min-1) and in the other group (n = 5) with 0.5% halothane. ⋯ Adequate recovery of respiratory muscle function occurred within 30 min of administration of atracurium at a time when there was less than 25% recovery of the tetanic response of the adductor pollicis muscle. It was concluded that recovery of the muscles of respiration from neuromuscular blockade by atracurium occurred more rapidly than recovery of the muscles of the hand, but an adequate tidal volume in the absence of other clinical signs should not be regarded as a reliable indicator of complete return of neuromuscular function.