Cotton Myer Subglottic Stenosis Grading Scale Grade Grade I Grade II Grade III Grade IV Percent of Obstruction 0 – 50 51 – 70 71 – 99 Complete Obstruction Myer CM, O’connor DM, Cotton RT. Proposed grading system for subglottic stenosis based on endotracheal tube sizes. Ann Otol Rhinol Laryngol. 1994;103(4 Pt 1):319-23.