Laryngeal mask airways (LMA) are widely used in patients receiving general anesthesia and are known to have the following advantages over the endotracheal tube: lower incidence of postoperative sore throat, lower incidence of cough during emergence, and lower incidence of postoperative vomiting. Although LMAs can be inserted without the use of muscle relaxants, a sufficient depth of anesthesia is necessary for placement. Remimazolam is a newer anesthetic that is ultra-short acting with a rapid onset and short context-sensitive half-life allowing for fast recovery. However, the dose of remimazolam needed for LMA insertion without muscle relaxants is not well known. This dose-finding study aims to find the ED50 and ED95 of a single bolus dose of remimazolam for LMA insertion without muscle relaxants in adult patients.

This is an interventional study done in a single group using the Dixon's up-and-down method which requires at least six success/failure pairs in the same direction. The primary endpoint of this study is to investigate the dose of remimazolam associated with 50% (ED50) and 95% (ED95) probability for adequate depth of anesthesia for LMA insertion without muscle relaxants. The beginning dose of remimazolam is 0.3 mg/kg, and when LMA insertion is successful, the dose will be decreased by 0.05 mg/kg in the next patient. When LMA insertion is unsuccessful (failed), the dose will be increased by 0.05 mg/kg in the next patient. Successful LMA insertion is defined as symmetrical chest wall movement and square-wave capnographic traces observed with manual ventilation.

Inclusion Criteria:

• Adult patients aged 19~65 year
• ASA class I~III
• Patients scheduled for orthopedic surgery under general anesthesia and eligible for LMA use.

Exclusion Criteria:

• Patient refusal
• Patients unable to read consent form
• Anticipated difficult mask ventilation
• Active URI or uncontrolled asthma
• Pneumonia
• Risk of aspiration such as GERD
• History of allergies to benzodiazepines
• Decreased liver or kidney function
• Pregnant or breastfeeding patients
• BMI > 30kg/m2
• History of substance abuse/addiction