British journal of anaesthesia
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The problem of ventilating small animals during nuclear magnetic resonance studies has been solved by using a T-piece system with a remotely controlled non-magnetic expiratory valve. This system does not affect the NMR signal, has minimal internal compliance and expiratory resistance, permits accurate control of peak airway pressure, and may be of use when animals have to be ventilated in hazardous surroundings.
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A microprocessor-controlled anaesthetic vaporizer is described. Fresh gas is mixed in the correct proportions using two pulsed solenoid valves and a proportion of this passes through a third pulsed solenoid valve and is bubbled through liquid halothane. The temperature of the liquid agent is measured and the pulse frequency is modified to give the correct vapour concentration for the set flow rate and measured temperature. ⋯ However, because of the large liquid volume available, nitrous oxide was found to dissolve in large quantities in the halothane. A small volume vaporizer which was continually replenished from a reservoir was designed. Measurements of the vapour concentrations emerging from such a vaporizer were made and were found to agree with the set values +/- 0.1% v/v.
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Randomized Controlled Trial Comparative Study Clinical Trial
Comparison of wakefulness with two anaesthetic regimens. Total i.v. v. balanced anaesthesia.
Fifty-five patients were assigned randomly to receive either a total i.v. anaesthetic based on a two-stage infusion of etomidate plus increments of fentanyl or a regimen based on inhaled nitrous oxide with i.v. fentanyl increments. Using the isolated forearm technique, 44% of the nitrous oxide group were found to be wakeful at some time during surgery, whereas only 7% of the etomidate group were wakeful. There was one case of awareness in the nitrous oxide group.
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The effect of changing the composition of the carrier gas from 66% nitrous oxide in oxygen to 100% oxygen was examined in three halothane vaporizers (Fluotec Mk 3, Drager Vapor 19 and Abingdon halothane vaporizer). All showed a transient increase in output following the discontinuation of the nitrous oxide. ⋯ The steady-state output of the vaporizers, once the transient response was over, was found to be lower with 100% oxygen as carrier gas than it had been with 66% nitrous oxide in oxygen. The difference was minor in the case of the Drager Vapor 19 (1% of indicated output) and Fluotec Mk 3 (5% of indicated output), but greater in the case of the Abingdon (15% of indicated output).
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Forty-five patients in four groups undergoing orthopaedic, upper abdominal, prolonged or cardiac surgery received a constant rate i.v. infusion of fentanyl 100 micrograms h-1, for 24 h starting 2 h before surgery. A single bolus dose was given i.v. at the induction of anaesthesia. ⋯ The elimination half-life was 7.3-9.7 h. This simple regimen produced effective analgesia.