Decrease in anesthetic gas concentration due to leak from vaporizer's cap

We experienced two cases of anesthetic gas leak from filler cap of the anesthetic vaporizer due to omitting to lighten up the filler cap. We detected the leak by patient's movement and isoflurane odor. These experiences forced us to measure isoflurane concentration at common outlet and adjacency of filler cap. Fresh gas flow were either oxygen 5L/min, or oxygen 1L/min plus nitrous oxide 2L/min. The setting of isoflurane concentration was varied from 1 to 3%. Then, we loosened the filler cap 45, 90, 180, 270 and 360 degree from tight shield. As a result, more than 90 degree's loosening resulted in the marked decrease even to almost 0 % in extreme occasion. Saturated gas leaked from the filler cap to operating room. In conclusion, we must confirm whether the filler cap is tightened at the inspection, and pay attention to the agent odor while in use.