The OPAs was used four different sizes as No. 8 (80 mm, green), 9 (90 mm, yellow), 10 (100 mm, red), and 11 (110 mm, orange) in regular sequence. The curvilinear distance from the incisors to the tip of the epiglottis was measured by FOB (Olympus LF-GP; Olympus Optical Co., Tokyo, Japan) with tape marking via each size of OPAs. The distance from the distal end of OPA to the tip of the epiglottis was calculated by the difference between measured distance from the incisors to the tip of the epiglottis via each OPA by FOB and typical distance from the flange to distal end of each OPA via inside tube of OPA. When the size of OPAs was longer than distance from the incisors to the tip of the epiglottis, OPAs were partly withdrawn and repositioned the distal end of OPAs is placed just above the tip of epiglottis. Then, the length from the incisors to the flange of OPAs was measured. .

Primary Outcome - 기술(Description) The distance from the distal end of OPA to the tip of the epiglottis was calculated by the difference between measured distance from the incisors to the tip of the epiglottis via each OPA by FOB and typical distance from the flange to distal end of each OPA via inside tube of OPA. When the size of OPAs was longer than distance from the incisors to the tip of the epiglottis, OPAs were partly withdrawn and repositioned the distal end of OPAs is placed just above the tip of epiglottis. Then, the length from the incisors to the flange of OPAs was measured. The optimal size of OPAs in individuals was defined that the distal end of OPA is placed the tip of epiglottis as close as possible without impingement on the epiglottis when the flange of OPA contact with the four central incisors.