The laryngeal mask is widely used in general anesthesia in children. Selection of an appropriately sized laryngeal mask airway (LMA) is critical to ensure safe and effective use of the device. In children, the appropriate size of the LMA to be used is usually determined by the patient's weight. Up to now, this is the gold standard method, but the weight-related technique is not always possible. The patient's weight is sometimes unknown or medical staff do not remember the relationship between weight and size. Moreover, there are no constant correlations between laryngeal airways and body indices such as height and weight, so that the standard method could cause an inappropriate size of laryngeal mask airway to be chosen. Researchers from Spain introduced a new technique to determine the size of the LMA in children by choosing the LMA that best matched the combined widths of the patient's index, middle and ring fingers, but needs to be formally evaluated in clinical application. In order to compare the application effects of two methods (weight-related and three-fingers), we designed a research plan.

The allocation sequence is generated by computer random number generation, and the allocation is placed in sequentially numbered opaque sealed envelopes by a non-investigator. Enrolment and data collection are performed by trained research staff who are not involved in the care of the patients. The treating clinicians are not blinded to the assignment group, but all other staff involved in both the collection and collation of data are blinded to group allocation. The primary measurement is the oropharyngeal leak pressure (OLP) at the recommended intracuff pressure. The secondary measurements included insertion time, fibreoptic view grade, insufficient ventilation, and the occurrence of complications such as postoperative sore throat. The sample size was calculated to be 390 by a statistical software based on previous research results. The continuous variables were expressed as means ± standard deviation (SD) whereas categorical variables were expressed as frequency and percentage for data description. P <0.05 was considered statistically significant.

Inclusion Criteria:

• children aged from 3 to 14yr, underwent elective ophthalmic surgery, had an American Society of Anesthesiologists physical status rating of I or II

Exclusion Criteria:

• Patients with lung disease, known airway problems, upper respiratory tract symptoms or any condition that may increase the risk of gastro-oesophageal regurgitation, or any anatomical abnormalities, especially those related to the head, neck or limbs.