Determination of insertion depth of flexible laryngeal mask airway in pediatric population—A prospective observational study

Study objective The purpose of this study was to determine the ideal insertion depth of the flexible laryngeal mask airway (FLMA) by elucidating the relationships between insertion depth and patient's age, body weight, height, and other parameters. We also evaluated an insertion technique that uses the change in intracuff pressure for proper positioning of the FLMA in cases where it is difficult to sense resistance during FLMA insertion. Design This study was a prospective observational study. Setting Participants were recruited from the Seoul National University Children's Hospital. Patients We enrolled 154 children aged ≤15 years with an American Society of Anesthesiologists physical status of I or II who were scheduled for ophthalmic surgery of <2 hours duration under general anesthesia. Interventions After induction of general anesthesia, FLMA insertion was guided by the change in intracuff pressure, measured using a manometer. The FLMA position was assessed using a fiberoptic bronchoscope. Measurements The FLMA insertion depth was measured at the end of each surgical procedure. A multiple linear regression model was then created using age, height, weight, nasal-tragus length, and sternal length. Main results The FLMA was successfully inserted in the first attempt in 134 patients using continuous monitoring of intracuff pressure. Using multiple linear regression analysis and the Durbin-Watson test, we found that insertion depth was best predicted by height and weight (r² = 0.777), and the resulting formula was as follows: insertion depth of FLMA (cm) = 7.0 + 0.04×height (cm) + 0.05 ×weight (kg). Conclusions The FLMA insertion depth can be calculated using height and weight. Continuous monitoring of intracuff pressure during FLMA insertion is a useful alternative insertion method in cases where resistance is difficult to sense.