Objective - To examine the accuracy and precision of isoflurane and sevoflurane anesthetic vaporizers. Sample Population - 5 identcal isoflurane and 5 identical sevoflurane vaporizers. Procedures - Oxygen flow rates from 0.02 to 10 L/min were used with different vaporizer dial settings. Agent concentrations were measured at the common gas outlet by use of a refractometer. Accuracy was defined as the difference between measured agent concentrations, and dial settings were expressed as a percentage of the applied dial settings. Precision was defined as SD of the measured agent concentrations for each combination of dial setting and flow. Results - Isoflurane values were generally greater than the dial settings. Accuracy of the isoflurane vaporizer was > 20% when 0.6% and 1 % was dialed. Accuracy of the sevoflurane vaporizer was always within ± 20% but decreased at 0.02 L/min flow and at combinations of high flow and high dial settings. Overall precision of the isoflurane vaporizer was better than that of the sevoflurane vaporizer. Conclusions and clinical relevance - A possible explanation for the inaccuracy of the isoflurane vaporizer may be that it was manufactured to be accurate with air but not oxygen, which must be accounted for when using the vaporizer with oxygen, especially with nonrebreathing systems. The sevoflurane vaporizer may not deliver accurate agent concentrations at high flow and high dial settings. Both vaporizers are suitable for clinical use with a wide range of oxygen flow rates if these precautions are properly addressed.
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