Accuracy of isoflurane, halothane, and sevoflurane vaporizers during high oxygen flow and at maximum vaporizer dial...

To assess the accuracy of isoflurane, halothane, and sevoflurane vaporizers during high oxygen flow and at maximum dial settings at room temperature and to test sevoflurane vaporizers similarly during heating and at low-fill states.

5 isoflurane, 5 halothane, and 5 sevoflurane vaporizers.

Vaporizers were tested at an oxygen flow of 10 L/min and maximum dial settings for 15 minutes under various conditions. All 3 vaporizer types were filled and tested at room temperature (21° to 23°C). Filled sevoflurane vaporizers were wrapped with circulating hot water (42°C) blankets for 2 hours and tested similarly, and near-empty sevoflurane vaporizers were tested similarly at room temperature. During each 15-minute test period, anesthetic agent concentration was measured at the common gas outlet with a portable refractometer and temperature of the vaporizer wall was measured with a thermistor.

For each vaporizer type, anesthetic agent concentrations and vaporizer wall temperatures decreased during the 15-minute test period. Accuracy of isoflurane and halothane vaporizers remained within the recommended 20% (plus or minus) deviation from dial settings. Heated and room-temperature sevoflurane vaporizers were accurate to within 23% and 11.7% (plus or minus) of dial settings, respectively. Sevoflurane vaporizers at low-fill states performed similarly to vaporizers at full-fill states.

Under these study conditions, the isoflurane and halothane vaporizer models tested were accurate but the sevoflurane vaporizers were not. Sevoflurane vaporizer accuracy was not affected by fill state but may be improved with vaporizer heating; measurements of inspired anesthetic agent concentrations should be obtained during the use of heated vaporizers.