Figure 60-9 Method of determining the percentage of airway obstruction. After easy passage of an endotracheal tube, a manometer is placed at the connection of the elbow of the anesthesia circuit and the endotracheal tube. A stethoscope is placed over the larynx and the circuit slowly pressurized. The pressure at which a leak is auscultated is matched with the age of the patient and the size endotracheal tube to assess the degree of laryngeal narrowing. It should be noted that this chart is based on one institution's experience and the manufacturer of the endotracheal tubes was not described; thus, the actual external diameter of the endotracheal tubes used is unknown. (Redrawn with modification from Myer CM 3d, O'Connor DM, Cotton RT: Proposed grading system for subglottic stenosis based on endotracheal tube sizes. Ann Otol Rhinol Laryngol 103:319–323, 1994.)