Currently, the main method for selecting an i-gel® size is based on the body weight recommendation (30-60 kg for size 3 and 50-90 kg for size 4) according to the manufacturer's recommendation. However, there is an overlapping in size selection in people weighing between 50 and 60 kilograms. Laryngeal mask airways are widely used for breast surgery, and this patient cohort is often weighed between 50-60 kilograms in National Taiwan University Hospital. Therefore, in this randomized clinical trial, the investigators will compare the ventilation efficacy of size 3 and size 4 i-gel® in anesthetized, paralyzed female patients weighing 50 to 60 kilograms who undergo breast surgery. Also, the investigators will record any side effects of size 3 and size 4 i-gel® in this cohort.

With the introduction of the laryngeal mask, it has been widely used for the management of airway during general anesthesia. Compared to the endotracheal tube, it has the advantages of easier and faster placing, reducing the proportion of a sore throat and other benefits. The i-gel® is a second-generation of the laryngeal mask. Compared to the classic laryngeal mask, it provides higher sealing pressure and better airway protection to reduce respiratory complications.

Choosing an appropriate size laryngeal mask is an important issue. Trauma during placing or positive ventilation failure may occur if the wrong size is selected. Currently, the main method for selecting an i-gel® size is based on the body weight recommendation (30-60 kg for size 3 and 50-90 kg for size 4) according to the manufacturer's recommendation. However, there is an overlapping in size selection in people weighing between 50 and 60 kilograms. Laryngeal mask airways are widely used for breast surgery, and this patient cohort is often weighed between 50-60 kilograms in National Taiwan University Hospital. Therefore, in this randomized clinical trial, the investigators will compare the ventilation efficacy of size 3 and size 4 i-gel® in anesthetized, paralyzed female patients weighing 50 to 60 kilograms who undergo breast surgery. Also, the investigators will record any side effects of size 3 and size 4 i-gel® in this cohort.

Keywords: Airway management; laryngeal mask airway; breast surgery

Inclusion Criteria:

• Age > 20 years old.
• ASA physical status I and II.
• Elective breast surgery.
• Female with a body weight of 50 - 60 kilograms.

Exclusion Criteria:

• High risk of aspiration. (defined as history of gastroesophageal reflux, hiatal hernia, previous gastric surgery, and those who take medications for disorders of gastrointestinal motility)
• Previous head & neck surgery.
• Previous head & neck concurrent chemoradiotherapy (CCRT)
• Reactive airway disease: chronic obstructive pulmonary disease (COPD), asthma, upper respiratory infection in recent two weeks
• Exposure to tobacco
• Pregnancy