A focused pre-procedure physical exam of the airway will in many cases provide predictive information regarding the anatomy of the airway visualized on direct inspection. The exam should also include assessment and documentation of dentition, including caps; implants; crowns; and loose, missing, or decaying teeth. Identification and removal of any personal ornamentation, such as tongue-piercing ornaments, should occur before undertaking airway manipulation.
The oropharynx includes the structures of the upper airway from the soft palate to the level of the hyoid bone. The oropharynx opens anteriorly into the mouth, is bounded laterally by the two palatine arches and tonsils, and includes the posterior tongue. The laryngopharynx includes the epiglottis and larynx, which in turn consists of the vocal folds and vocal cords; the thyroid, cricoid, and arytenoid cartilages; and the intrinsic muscle of the larynx. The larynx begins where the upper airway divides to form the laryngeal inlet and the upper esophagus. The epiglottis is a cartilaginous flap attached to the posterior tongue, which forms a protective flap between the trachea and the upper esophagus.
Many major nerves contribute to pharyngeal and laryngeal function. Pharyngeal function is governed by cranial nerves IX, X (pharyngeal plexus), and XI (pharyngeal branch), which control elevation and shortening of the pharynx, alterations in palate position, the size of the pharyngeal lumen, and bolus transport of food in the esophagus. Motor innervation of the larynx is via the external and recurrent laryngeal branches of cranial nerve X. In addition, the facial nerve (cranial nerve VII) and cervical spinal nerves (C1-C3) contribute to motor function of the upper airway via actions of the mylohyoid muscle on the hyoid bone to pull the larynx up and the infrahyoid muscles, which pull the larynx down. Mandibular action during phonation is also controlled by the mandibular branch of the trigeminal nerve. Sensory innervation of the larynx is via the internal laryngeal branch of the vagus nerve (cranial nerve X) above the vocal folds and the recurrent laryngeal branch of the vagus nerve below the vocal folds.
Important internal landmarks involved in laryngoscopy and intubation include the epiglottis, the vallecula, the intrinsic cartilages of the larynx (arytenoids, thyroid, and cricoid), the true and false vocal cords, and the hyoid bone.
External Anatomic Features
Important external landmarks include the mental protuberance of the mandible, thyroid cartilage, hyoid bone, and cricoid cartilage. Anatomic features of direct relevance to laryngoscopy include extent of mouth opening, extent of jaw subluxation, ability to flex and extend the neck, neck circumference, tongue size protrusion, ability to visualize the uvula or soft palate with mouth opened and tongue protruded in the sitting posting without phonation (Mallampati score), mandibular size, mentohyoid distance, thyromental distance, and protuberant dentition. These measures are not sensitive or specific enough to predict whether the view will be limited on direct laryngoscopy. Limitations of movement, low Mallampati score, and short anatomic distances may warrant alternative strategies to endotracheal intubation.
The extent of visualization of the glottal opening under direct laryngoscopy is categorized by standardized grade (Cormack-Lehane scale) and is useful for objective description of the view for future airway management.
With a Macintosh blade, upward (axial) force on the hyoepiglottic ligament raises the epiglottis to reveal the glottal opening. With the straight Miller blade, the upward force under and against the epiglottis pulls the entire structure superiorly. External pressure on the cricoid cartilage (located just inferior to the thyroid cartilage and cricothyroid membrane) may in some cases improve the view of an anteriorly displaced larynx. A related intervention on the larynx, the BURP (backward, upward, rightward pressure) maneuver, has also been reported to improve visualization of the vocal cords in some patients.