British journal of anaesthesia
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We studied radiographically 11 patients in whom direct laryngoscopy proved difficult and 100 control (general population) subjects. The vertical distance between the mandible and the hyoid bone (mandibulohyoid distance) was measured and the positions of the mandibular angle and hyoid bone determined in relation to the cervical vertebrae. We found that the mandibulohyoid distance was substantially longer in patients whose trachea was difficult to intubate; the mandibular angle tended to be positioned more rostrally in both men and women, and the hyoid bone tended to be positioned more caudally in women. This suggests that a relatively short mandibular ramus or a relatively caudal larynx may be important, unfavourable anatomic factors in difficult laryngoscopy.
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Using the Brüel & Kjaer Anaesthetic Gas Monitor type 1304, we have monitored the output of 94 anaesthetic agent vaporizers (Fluotec 3:58, Enfluratec 3:24, Isotec 3:12), in seven departments of anaesthesia, at different dial settings and flow rates. The range of output, for one type of vaporizer and dial setting (flow: 6 litre min-1) was largest with the Fluotec 3 (0.85-1.55% when dial set to 1%) and smallest with the Isotec 3 (0.85-1.15% when dial set to 1%). In determining the number of vaporizers with unacceptable inaccuracy, we applied acceptance limits of +/- 15% relative on each vaporizer and each dial setting. ⋯ Even when some specific conditions (vaporizers giving output beyond the limits at any two or more dial settings; output beyond the limits in the clinically relevant range (0.5-2%)) were added, a substantial number of vaporizers did not perform within the limits. We found a significantly greater accuracy of the vaporizers after 3-monthly calibration checks (P < 0.05) compared with vaporizers undergoing service and calibration only annually. Using a questionnaire, we found that fewer than 30% of the anaesthetists using the vaporizers would accept aberrance beyond +/- 10% relative of the dial setting.