Endotracheal Dilator to Improve Oxygenation

The purpose of the study is to prospectively assess the use of a modified tracheal balloon dilator in children (\<13 years old) with subglottic or tracheal stenosis. The hypothesis is that the device will effectively dilate the stenotic segment, whilst maintaining oxygenation (if applicable). The primary aim is to measure the stenosis prior to, and after dilatation; using diameter and the modified Myer-Cotton grading system. Secondary aims include assessment of stenosis at six-week follow-up and monitoring arterial oxygenation nadir (using peripheral plethysmography) during the procedure.