The distance between the grille of the laryngeal mask airway and the vocal cords. Is conventional intubation through the laryngeal mask safe?

The distance between the grille of the laryngeal mask airway and the vocal cords was measured with a fibreoptic bronchoscope in 30 male and 30 female patients. The mean distance was 3.6 cm (SD 0.5 cm; range 2.5-4.7 cm) in males and 3.1 cm (SD 0.5 cm; range 2.0-4.2 cm) in females. These results suggest that the cuff of an uncut 6.0 mm tracheal tube would often lie between the vocal cords when the tube is fully inserted through a laryngeal mask airway. To avoid this complication, the tracheal tube must protrude more than 9.5 cm beyond the grille of the laryngeal mask airway. When either neck extension or flexion is required, the laryngeal mask airway should be removed as the margin of safety is small.