British journal of anaesthesia
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A case of closed injury to the cervical portion of the trachea, caused by a wheat-threshing machine, is reported. The patient presented with extensive subcutaneous emphysema, but without any respiratory distress. The unique problem faced during the management of an anterolateral tear of the trachea is highlighted.
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Comparative Study
Neuromuscular blocking and autonomic effects of vecuronium and atracurium in the anaesthetized cat.
The effects of vecuronium and atracurium on neuromuscular transmission, on the responses of the heart rate to vagal stimulation and on the responses to preganglionic stimulation of the nictitating membrane were compared in the chloralose-anaesthetized cat. Vecuronium was four times more potent than atracurium as a neuromuscular blocking agent, whereas the two compounds had similar potencies in blocking the effects of stimulation of the cardiac vagus. The vagal/neuromuscular ratios measured at 50% inhibition were 96 for vecuronium and 25 for atracurium. ⋯ Both compounds had longer time-courses of action than suxamethonium. Very large doses of vecuronium decreased the responses of the preganglionic stimulation of the nictitating membrane, suggesting that at high doses the compound possesses ganglion blocking activity. Large doses of atracurium also decrease the nictitating membrane responses and, in some cats, contractions of the nictitating membrane associated with increases in heart rate and arterial pressure were observed.
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A method of closed-circuit anaesthesia has been developed in which the end-tidal concentration of the volatile anaesthetic agent used is controlled automatically using a closed-loop servo system. End-tidal anaesthetic concentrations, measured by the Engstrom EMMA, were maintained in the closed circuit by direct liquid injection. The system was tested in the laboratory and in clinical use (12 subjects). ⋯ The major sources of error in the method were the result of zero offset in the Engstrom EMMA which in turn was caused by humidity and the intrinsic characteristic of the simple proportional controller used. These errors were easily correctable, and end-tidal halothane concentration could be controlled to within 0.1%. Mean halothane vapour uptake at a constant end-tidal concentration of 0.8% was 114 ml min-1 at 1 min, 36 ml min-1 at 5 min, 29 ml min-1 at 10 min and between 22 and 18 ml min-1 at 20-35 min.
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The pharmacokinetics of ketamine 2 mg kg-1 i.v. and 6 mg kg-1 i.m. were investigated in nine children undergoing minor surgery. After either route of administration plasma ketamine concentrations were similar to those found in adult patients receiving the same dose, except at later times after i.v. injection, when concentrations were smaller in children. Also, absorption after i.m. injection appeared to be more rapid in children. ⋯ Concentrations of ketamine upon awakening in a further group of nine children receiving ketamine as the sole anaesthetic showed large inter-individual variation. The concentrations were greater than those previously reported for adults. The greater dose requirements in children, compared with adults, are probably attributable to pharmacodynamic rather than pharmacokinetic factors.
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Twenty-six patients were anaesthetized with isoflurane (Forane) in oxygen using a completely closed-circuit breathing system to which liquid isoflurane was injected. The rate of injection was controlled to maintain the end-tidal concentration at a pre-set value (1.5% = 1.3 MAC). ⋯ It was found to average 44.5 ml of vapour at 2 min, 23.7 ml at 10 min and 19.4 ml at 30 min. Attempts were made to correlate the data with anthropometric measurements.