Changes and closure grades of the laryngeal vestibule in different positions after anesthesia induction

The aim of this study was to observe changes in the laryngeal vestibule under head extension or in neutral position with or without the chin lifted after anesthesia induction.

After anesthesia induction, a flexible bronchoscope was used to observe the status of the laryngeal vestibule under four positions. Then, the degree of laryngeal vestibule closure was graded. The grading scores and the incidence of severe closure under these four positions were compared. The factors that may be related to the severe closure and potential contributions of head extension and chin lifting were also analyzed. When laryngeal mask was applied, the change in the laryngeal vestibule state was observed through the laryngeal mask after placement.

The closure scores of the laryngeal vestibule were significantly different among these four positions (P<0.001). The incidence of severe closure was highest in the neutral head position without the chin lifted. Regression analysis showed that age and snoring were associated with severe closure of the laryngeal vestibule. Both head extension and chin lifting could decrease the risk of severe closure of the laryngeal vestibule, and head extension was more important than chin lift. After laryngeal mask placement, the severely closed laryngeal vestibule can be further opened up to grades 1-2.

The neutral position of the head after anesthesia induction may cause complete closure of the laryngeal vestibule. The best way to keep the laryngeal vestibule open is head extension with the chin lifted, while most the laryngeal vestibules will be severely closed in the neutral position without the chin lifted.