Dynamic Interaction of Craniofacial Structures during Head Positioning and Direct Laryngoscopy in Anesthetized Patients with and without Difficult Laryngoscopy

Abstract

Background We lack fundamental knowledge of the mechanisms of difficult laryngoscopy despite its clinical significance. The aim of this study was to examine how head positioning and direct laryngoscopy alter arrangements of craniofacial structures. Methods Digital photographs of the lateral view of the head and neck were taken at each step of head positioning and direct laryngoscopy in age- and body mass index-matched patients with (n = 13) and without (n = 13) difficult laryngoscopy during general anesthesia with muscle paralysis. The images were used for measurements of various craniofacial dimensions. Results Both simple neck extension and the sniffing position produced a caudal shift of the mandible and a downward shift of the larynx, resulting in an increase of the submandibular space. Direct laryngoscopy during the sniffing position displaced the mandible and tongue base upward and caudally, and the larynx downward and caudally, increasing the submandibular space and facilitating vertical arrangement of the mandible, tongue base, and larynx to the facial line. These structural arrangements in response to direct laryngoscopy were not observed in patients with difficult laryngoscopy, whereas head positioning produced similar structural arrangements in patients with and without difficult laryngoscopy. Conclusion Increase in the submandibular space and a vertical arrangement of the mandible, tongue base, and larynx to the facial line seem to be important mechanisms for improving the laryngeal view during head positioning and direct laryngoscopy. Failure of these structural arrangements in response to direct laryngoscopy may result in difficult laryngoscopy.