echo - endoscopes are much stiffer and thicker than regular endoscopes . during the procedure of endoscopic ultrasound ( eus ) procedure , water irrigation is a very useful for imaging but very dangerous if the patient receive the procedure under anesthesia without intubation . in this study , we evaluated the safety and effectiveness of nitrous oxide ( n2o ) ( 70% ) for eus . among 4230 patients who underwent eus from december 2012 to december 2013 , 347 out patients who need irrigation during the procedure were enrolled and divided into group a. group a ( n2o sedation group , n = 162 ) and group b ( no sedative group , n = 185 ) . for group the mixture rate of n2o and o2 was 45 - 65% and controlled by nurses according to individual effect . the cardiorespiratory functions , procedure duration , complications , and visual analog scale ( vas ) of the patient and examiner satisfaction were compared . both group had comparable diagnostic accuracy , but vas of the patients who received n2o sedation was higher than that in group b ( 7.5 vs. 4.5 , p < 0.05 ) and the examiner procedural satisfaction ratings of group a was also better than that of group b ( 8.1 vs. 5.1 , p < 0.05 ) ; most patients in group a reported willingness to reconsider n2o for a future eus . n2o for eus is comfortable , safe and feasible , especially for the procedures that need irrigation .