The Influence of Head and Neck Position About Oropharyngeal Leak Pressure and Sealing Between the Laryngeal Mask and Vocal Cord Using Different Types of Supraglottic Airway Device

The investigators select adult patients,who are 20-80yrs old and ASA physical status I or II, receiving minor surgery, ex: breast surgery or cystoscope, participated in this randomized cross-over trial. Patients were excluded if they were in the above condition. The patient is at high risk of aspiration, ex:obesity, pregnancy upper GI bleeding or not enough fasting time. The patient could not open mouth or upper airway obstruction. The patient receive major surgery, ex: heart, brain, lung, liver, kidney surgery. The patient has abnormal heart and lung function. The patient received different types of supraglottic airway device like proseal LMA,ambu LMA, air Q LMA or igel LMA by draw, then the patients will be divided into different groups.In the preoperative period, the investigators documented oropharyngeal leak pressure in these selected positions: neutral position( 0 degree),and rotation 15, 30,45, 60 degrees, etc. However, oropharyngeal leak pressure was measured by closing the expiratory valve of the circle system at fixed O2 flow 3L/min and 20 cm H2O. If the ambu bag is flattening, the investigators will think the leakage happened between the laryngeal mask and our vocal cord. Then the investigators use fiberscope to observe the condition between the epiglottis and the laryngeal mask. The investigators wanted to compared the mean leak pressure at different head and neck rotation position,ex:neutral,30,45,60 degrees,by using many different types of supraglottic airway device. The observers define the relationship between epiglottis and vocal cord to describe the condition when the patient is at different degree of head and neck position. Grade I is vocal cord completely visible. Grade IIA is only partially vocal cord visible and epiglottis noted. Grade IIB is no vocal cord visible and only epiglottis noted. Grade III is other condition, ex:trapped epiglottis or no epiglottis visible.