Prediction of difficulty in direct laryngoscopy

Abstract

To establish easily measurable and reproducible preoperative parameters predicting difficult laryngeal exposure in direct laryngoscopy. A prospective study including 71 patients who underwent transoral microsurgery for benign or malignant lesions of the larynx was performed in our department from January 2021 to November 2021. Physical assessment included the Mallampati score, weight, height, body mass index and measurements of seven parameters in the cervical region. Eleven parameters were measured on the cervical radiography film. Among our patients, 19 were included in the difficult laryngeal exposure (DLE) group. High Mallampati and Cormack scores were significantly associated with DLE (p = 0.005 and p < 0.0001). Limited mouth opening, direct thyromental distance (DTMD) < 67 mm in neutral position, DTMD < 82 mm and sternomental distance < 157 mm at full head extension were statistically related to DLE. For radiological assessment, the effective length of the maxilla and the atlanto-occipital distance were related to DLE. Using stepwise logistic regression, only the effective length of the maxilla and atlanto-occipital distance were selected as independent predictors for DLE (p: 0.015 and 0.001). Preoperative prediction of DLE is useful for both surgeons and patients. The length of the maxilla and the atlanto-occipital distance were found to be independent risk factors for DLE. This highlights the effect of overgrowth of the maxilla, protrusion of the upper teeth and limited extension of the cervical spine as the major risk factors for difficult laryngeal exposure.

Figure 1

Physical measurements in the neutral position. 1: Hyomental distance (HMD): Distance between the chin and the hyoid bone. 2: Direct thyromental distance (DTMD): Distance between the chin and the thyroid cartilage. 3: Vertical thyromental distance (VTMD): Vertical distance between the chin and the thyroid cartilage. 4: Horizontal thyromental distance (HTMD): Horizontal distance between the chin and the thyroid cartilage. 5: Sternomental distance (SMD): Distance between the chin and the sternum.

Figure 2

Radiographic measurements. A: Distance between the tip of the upper incisors and the upper border of the body of the hyoid bone. B: Distance between the tip of the upper incisors and the thyroepiglottic junction. C: Distance between the tip of the upper incisors and the temporomandibular joint (effective maxilla length). D: Distance between (along the upper teeth) the tip of the incisors and the point where the line intersects a perpendicular line extending from the temporomandibular joint. E: Distance between (perpendicular line) the temporomandibular joint and Line D (effective height of maxilla). F: Distance between the tip of the lower incisors and the temporomandibular joint. G: Distance between the tip of the alveolus immediately behind the third molar tooth and the lower border of the mandible (posterior depth of the mandible). H: Distance between the tip of the lower incisors and the anterior limit of the mandible’s lower border (anterior depth of the mandible). I: Distance between the upper border of the C1 body and the lower border of the C5 body. J: Distance between the occiput and the spine of C1 (at maximum head extension) (atlanto-occipital distance).

Figure 3

Tyro-mandibular angle. TMA: thyroid-mandible angle: the angle between the line of the mandibular angle to the prominence and the line from the thyroid notch to the mandible.