Canadian Anaesthetists' Society journal
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Continuous positive airway pressures (CPAP) of 0.49 kPa and 0.98 kPa were applied to ten healthy volunteers and nine critically ill patients with acute respiratory failure. A modified Godart-Statham NV 16003 spirometer was used to measure respiratory frequency (f), tidal volume (VT), oxygen consumption (VO2), and changes in functional residual capacity (delta FRC). During CPAP of 0.49 kPa, volunteers had a decrease in f, and increased VT and minute volume (MV). ⋯ VO2 in the patient group rose significantly at 0.49 and 0.98 kPa CPAP. Some of the patients were uncomfortable with 0.49 kPa pressure, while all the patients were distressed at 0.98 kPa CPAP. The effects of increased oxygen consumption and patients discomfort should be considered in critically ill patients receiving CPAP therapy.
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Comparative Study
An evaluation of gas density dependence of anaesthetic vaporizers.
Four commonly used vaporizers were studied for the effect of carrier gas density on vaporizer output. Vapour concentrations from a halothane Cyprane (Fluotec) Mark 2 increased in relation to the density of carrier gas, whereas the concentrations delivered by an enflurane Ohio vaporizer decreased. The halothane Cyprane (Fluotec) Mark 3 and enflurane Cyprane vaporizers were largely independent of density. Of clinical importance, nitrous oxide/oxygen (75/25), compared with oxygen alone, increased the vapour concentration outputs of the halothane Mark 2 up to 30% and decreased the outputs of the enflurane Ohio unit up to 20%.
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Comparative Study
Porcine malignant hyperthermia--failure of dantrolene dose response to diagnose susceptibility (halothane effect).
Dantrolene, a skeletal muscle relaxant, has been proven prophylactic and therapeutic for malignant hyperthermia (MH) in swine. This study examined the feasibility of using a dantrolene dose response as measured by indirectly evoked foretoe twitch depression as a means to safely discriminate MH susceptibility in swine. The effect of halothane on the dantrolene response was quantified. ⋯ Under halothane, the MHS animals had significantly augmented dantrolene response compared to MHR pigs, but three MHS animals had developed the MH syndrome prior to receiving dantrolene. We conclude that dantrolene muscle relaxant dose response cannot be used as a diagnostic test for MHS in swine. Halothane augments dantrolene twitch depression in MHS swine.
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Comparative Study
Experimental evaluation of local anaesthetic solutions using rat infraorbital nerve block.
The analgesic effectiveness of various local anaesthetic solutions was measured in the distribution of the infraorbital nerve of the rat. Using Sprague-Dawley rats sedated with phenobarbitone 25 mg/kg intraperitoneally and a simple stereotactic technique, 0.2 ml of solution was deposited at the infraorbital notch. The onset and duration of analgesia were ascertained by timing the unilateral absence of aversive response to pinching the upper lip, tested at intervals of five minutes. ⋯ Solutions were tested on sets of eight animals weighing 500--600 g. The average duration (minutes +/- S. D.) of analgesia produced by the respective injectates was as follows: Lidocaine 0.5% -42+/-12 Lidocaine 1.0% -47+/-10 Mepivacaine 0.5% -58+/-13 Mepivacaine 1.0% -78+/-23 Procaine 0.5% -0+/-0 Procaine 1.0% -34+/-10 Procaine 1.5% -46+/-13 2-Chloroprocaine 1.5% -38+/-9 Bupivacaine 0.5% -100+/-40 Etidocaine 1.0% -59+/-25 Tetracaine 0.2% -0+/-0 Tetracaine 0.3% -0+/-0 Comparison with other animal models used to evaluate conduction block indicates that this technique affords an improved, standardized and reliable experimental guide to the clinical analgesic properties of local anaesthetic agents.
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Medical students should learn certain facts and comprehension of these facts during an elective month spent in a Department of Anaesthesia. This enables them to make the most of the tutorial situation in which they work with clinical anaesthetists. ⋯ They were associated with an improvement in student performance and were acceptable to students and instructors. However, computer based instruction should only be used to improve certain learning situations and should not be employed as an alternative to interaction with physicians and patients.