British journal of anaesthesia
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Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). ⋯ Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limits.
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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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Randomized Controlled Trial Clinical Trial
Effect of heat conservation during and after major abdominal surgery on muscle protein breakdown in elderly patients.
Changes in mean body temperature and muscle protein metabolism were studied in elderly patients undergoing large bowel surgery. Two groups were studied: in one, efforts were made to maintain the patients normothermic during and after surgery by warming the fresh gases, the i.v. fluids, by placing warmed cotton padding around the exposed parts of the body and by covering the patients with a metallized plastic sheet in the recovery period. ⋯ The excretion of the amino acid 3-methylhistidine (3-MeH), an indicator of muscle protein breakdown, and urea nitrogen loss were measured in the urine collected the day before, and on the 2nd and 4th postoperative days. Prevention of heat loss during and after surgery caused a significant decrease in muscle protein degradation and nitrogen loss.
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Comparative Study
Emergency intubation of the trachea facilitated by suxamethonium. Observations in obstetric and general surgical patients.
The relationship between the time of onset of neuromuscular blockade and the time at which laryngoscopy was attempted was studied in patients presenting for emergency obstetric or emergency general surgical procedures. "Train-of-four" stimulation and visual observation of the evoked twitch response in the hand were used as a measure of the degree of neuromuscular blockade. The attendant anaesthetist was unaware of the response to the peripheral nerve stimulator. Intubation preceded complete neuromuscular blockade; in the obstetric patients there was no correlation between the two times. The use of a peripheral nerve stimulator should allow the anaesthetist to perform intubation in emergency situations with a greater degree of safety.