A Simple Endoscopic Technique for Measuring the Cross-Sectional Area of the Upper Airway in a Rabbit Model

Objective: Validate an accurate and reproducible method of measuring the cross-sectional area (CSA) of the upper airway. Subjects and Methods: This is a prospective animal study done at a tertiary care medical treatment facility. Control images were obtained using endotracheal tubes of varying sizes. In vivo images were obtained from various timepoints of a concurrent study on subglottic stenosis. Using a 0° rod telescope, an instrument was placed at the level of interest, and a photo was obtained. Three independent and blinded raters then measured the CSA of the narrowest portion of the airway using open source image analysis software. Results: Each blinded rater measured the CSA of 79 photos. The t testing to assess for accuracy showed no difference between measured and known CSAs of the control images (P =.86), with an average error of 1.5% (SD = 5.5%). All intraclass correlation (ICC) values for intrarater agreement showed excellent agreement (ICC >.75). Interrater reliability among all raters in control (ICC =.975; 95% CI,.817-.995) and in vivo (ICC =.846;, 95% CI,.780-.896) images showed excellent agreement. Conclusions: We validate a simple, accurate, and reproducible method of measuring the CSA of the airway that can be used in a clinical or research setting.