1. The muscle relaxants can improve the conditions of laryngeal mask incubation and reduce the related complications (such as laryngeal spasm and postoperative throat pain)
2. The dosages of muscle relaxants used in various researches vary greatly.
3. We are planning use the most classical method for determining the ED50 or half effective concentration of cis-atracurium using sequential method, which is also called " up and down method" and " ladder method".

The concordance of the current research is that muscle relaxants can improve the conditions of laryngeal mask incubation and reduce the related complications (such as laryngeal spasm and postoperative throat pain ) of laryngeal mask incubation. It is necessary to use muscle relaxants in laryngeal mask incubation under non-special circumstances. However, the dosages of muscle relaxants used in various researches vary greatly of normal endotracheal intubation. Previous studies have shown that the amount of muscle relaxant required for laryngeal mask intubation is smaller than that required for endotracheal intubation. Although the dosage of muscle relaxant required for tracheal intubation can ensure the smooth insertion of laryngeal mask airway, laryngeal mask airway is mostly used for short surgery, which is prone to postoperative muscle relaxation residue and prolongs the recovery. We planning use the most classical method for determining the ED50 or half effective concentration of cis-atracurium using sequential method, which is also called " up and down method" and " ladder method".

Inclusion Criteria:

1. ASA Ⅱ~Ⅲlevel;
2. BMI18.5-30；
3. Those who intend to undergo short urological surgery ( operation time < 1h );
4. Age 25~75 years
5. Estimated amount of bleeding < 5ml / kg.

Exclusion Criteria:

1. Neuromuscular diseases or metabolic diseases;
2. Preoperative complicated with water and electrolytes disorders ( such as hypokalemia and hypocalcemia );
3. Serious hepatic and renal insufficiency and serious heart and lung diseases;
4. Predictable difficult airway;
5. Take drugs ( such as aminoglycoside, polymyxin, phenytoin sodium, carbamazepine, etc. ) that affect the nerve-muscle transmission function or the efficacy of muscle relaxants before surgery;
6. Muscle relaxation drug allergy;
7. Previous history of alcoholism or drug abuse.

patients in Xuanwu Hospital for elective short urological surgery are selected.

One day before surgery, visitors recorded basic information such as the patient's sex, age, BMI, ASA grade in the ward, carried out airway evaluation, and recorded the mouth opening to make sure they can be included