ACCURACY OF 94 ANAESTHETIC AGENT VAPORIZERS IN CLINICAL USE

Using the Brüel & Kjæ Anaesthetic Gas Monitortype 1304, we have monitored the output of 94 anaesthetic agentvaporizers (Fluotec 3: 58, Enfluratec 3: 24, Isotec 3. 12),in seven departments of anaesthesia, at different dial settingsand flow rates. The range of output, for one type of vaporizerand dial setting (flow: 6 litre min^–1 was largest withthe Fluotec 3 (0.85–1.55% when dial set to 1%) and smallestwith the Isotec 3 (0.85–1.15% when dial set to 1 %). Indetermining the number of vaporizers with unacceptable inaccuracy,we applied acceptance limits of ± 15% relative on eachvaporizer and each dial setting. Using a flow of oxygen 6 litremin^–1 17% of Fluotec 3, 8% of Isotec 3 and 71 % of Enfluratec3 vaporizers had outputs outside those limits. Even when somespecific conditions (vaporizers giving output beyond the limitsat any two or more dial settings; output beyond the limits inthe clinically relevant range (0.5–2%)) were added, asubstantial number of vaporizers did not perform within thelimits. We found a significantly greater accuracy of the vaporizersafter 3-monthly calibration checks (P < 0.05) compared withvaporizers undergoing service and calibration only annually.Using a questionnaire, we found that fewer than 30% of the anaesthetistsusing the vaporizers would accept aberrance be yond ±10% relative of the dial setting. (Br. J. Anaesth. 1993; 71:453–457)