Bronchoscopy:
Bronchoscopy is an essential and useful tool to assess the airway and identify the site and number of complete rings. This however needs to be performed by a skilled operator as iatrogenic oedema of the tracheal mucosa may completely obstruct an already narrow airway. Rigid endoscopy can also be used, however views may be limited if there is significant tracheal stenosis. Assessment of the airway via  laryngeal mask is ideal as it avoids instrumentation in the larynx.8,37,38Maintaining the airway and ensuring ventilation and oxygenation are paramount tasks for the anaesthetist especially in critical cases.38 In neonates and infants, typically a 2.8mm flexible bronchoscope is used.37 If the obstruction is severe, a 2.2 mm suction fiberoptic scope can pass through distal tracheal stenosis to visualise the carina. Topical vasoconstrictor epinephrine may reduce procedural risk.
Dynamic bronchoscopy may also be useful to differentiate fixed stenosis from distal malacia , the latter occurring between 20 and 40% of cases. Tracheobronchomalacia contribute significantly to long-term morbidity and need for long-term ventilation, tracheostomy or highly specialised intervention such as tracheal and bronchial stents.36,39,40 The typical bronchoscopic features of LPA sling are shown in figure 9 with mild cranial compression and left bronchus origin narrowing posteriorly  by the retro-tracheal LPA (Type Ia) to significant carinal and right distal lateral tracheal wall compression obscuring the view of the carina into the right main bronchus. The severe end of the spectrum with multiple complete rings and  an absent trachealis muscle (figure 9c). These are best seen with a well suctioned airway clear of secretions as these may obscure the presence of complete rings along the trachea floor. If tracheal stenosis is severe it may not even be possible to view the carina - in this instance bronchograms are very informative.7