Anaesthesia
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Three possible factors predisposing to Althesin hypersensitivity, namely total dose, method of administration, either by bolus dose or infusion, and pregnancy have been studied in patients receiving the drug for the first time. Of 137 patients given Althesin, four exhibited clinical signs of mild hypersensitivity, while C3 conversion alone, indicative of a subclinical reaction, was seen in a further six patients. No reactions were observed in two control groups in whom anaesthesia was induced with thiopentone. Neither the total dose nor method of administration appeared consistently to influence the incidence of reactions, but eight of the ten patients producing an altered response to Althesin were pregnant.
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In fit unpremedicated patients undergoing minor operations and who were ambulant on the afternoon of the operations, pretreatment with magnesium sulphate given intravenously did not reduce the incidence of suxamethonium induced myalgia below that in a similar series who received no prophylactic therapy. The injection of magnesium in conscious patients is followed by unpleasant side effects.
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Arterial plasma concentrations of lignocaine were studied in fifteen adult patients following insertion of a tracheal tube whose cuff area was smeared with 5% lignocaine ointment. Twelve patients had 2 ml of ointment (114 mg) and samples were taken every 5 minutes until 30 minutes and in eight of the 12 patients at 40, 50 and 60 minutes after insertion and inflation of the tracheal tube and cuff. ⋯ In the 2 ml lignocaine group mean plasma lignocaine levels were 1.9 (SD 0.9) micrograms/ml at 10 minutes, 2.3 (SD 0.8) micrograms/ml at 20 minutes, 2.3 (SD 0.8) micrograms/ml at 30 minutes and 1.7 (SD 1.0) micrograms/ml at 60 minutes. After 1 ml of lignocaine, levels were 1.2 (SD 0.1) micrograms/ml at 10 minutes, 1.1 (SD 0.7) micrograms/ml at 20 minutes, 0.8 (SD 0.3) micrograms/ml at 30 minutes and 0.75 (SD 0.1) micrograms/ml at 60 minutes.
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The absorption of nitrous oxide in halothane was studied by bubbling nitrous oxide and nitrous oxide/oxygen gas mixtures through a halothane bottle, using 100% oxygen as a control. The gas volume emerging from the halothane bottle was measured each minute, over a period of up to 15 minutes. ⋯ However, in the presence of nitrous oxide, the initial flow rate of the gas emerging from the halothane bottle was greatly diminished, but then accelerated rapidly to reach that obtained with oxygen. The results suggested that nitrous oxide dissolved in large quantities in halothane, and the data are consistent with an Ostwald coefficient in excess of 4.0.