Anaesthesia
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Changes in cuff pressure and volume of tracheal tubes were studied in 60 patients undergoing lower abdominal surgery under general anaesthesia with nitrous oxide and oxygen as the anaesthetic gas mixture. The cuffs were inflated with either anaesthetic gas mixture or air. ⋯ The pressure in the air filled cuffs increased steadily throughout the procedure and reached level high enough to impede microcirculation in the tracheal mucosa within one hour. We conclude that filling the cuff with anaesthetic gas mixture is a simple and reliable way to achieve stable cuff pressure during anaesthesia.
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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.