Airway assessment based on a three column model of direct laryngoscopy
Airway assessment has remained a problematic area, largely due to the low sensitivities, specificities and/or positive predictive values of most bedside tests. In this paper, a structured overview of the common preoperative airway assessment tests is presented, based on a model for direct laryngoscopy that has been previously described. This model is composed of three columns: anterior, middle and posterior. The anterior column tests are classified into the assessment of volume and compliance of the submandibular space, the range of movement of the temporomandibular joints and the flexibility of the stylohyoid ligament. Reductions in volume of the anterior column may be absolute or relative. An absolute reduction may occur with shortening of either the incisor-hyoid distance, the temporomandibular joint-incisor distance or the temporomandibular joint-temporomandibular joint distance. A relative reduction may be seen with either prominent upper front incisors or large tongues. Testing of the middle column includes a history and physical examination of the upper respiratory system, imaging of the airway (such as X-ray, computed tomography scans and/or magnetic resonance imaging scans) and nasopharyngoscopy. The posterior column may be assessed by the range of movement of the neck, especially the range of extension of the occipito-atlanto-axial complex. By integrating common tests of the anterior, middle and posterior columns within this three-column model, the practitioner may be better positioned to understand the complexity of direct laryngoscopy in both normal and difficult airway scenarios.