Divide the Airway
After more than twenty years of being airway obsessed, I recently began to gain a different perspective of the anatomy and clinical challenges of airway management. I believe it is useful to divide the airway into three sections to improve our anatomic understanding, and more importantly, to guide therapeutic intervention (see Figure 3):
- The upper airway includes the nasopharynx, mouth, and the hypopharynx down to the larynx. The upper airway is the most common site of airway obstruction due to the soft tissue structures of the palate, tongue, and epiglottis.
- The middle airway runs from the laryngeal cartilages (larynx) to the bronchi. It is normally patent, stented open by the rigidity of the thyroid and cricoid cartilage, and the tracheal rings.
- The lower airway includes the lungs and alveoli, where gas absorption occurs across the alveolar-capillary membrane.
To decipher the sorcery of the airway, we must appreciate how sedation, positioning, and our therapeutic interventions and techniques affect the airway at all three levels. Gravity is the enemy of both upper and lower airway patency when the patient is in a supine position. Supine positioning (coupled with poor muscular tone) causes the tongue to fall backwards against the soft palate and contact the posterior pharynx. Oral airways and/or nasopharyngeal airways are often needed to keep the soft palate and tongue from obstructing the airway. This is problematic because some patients may have respiratory depression or poor tone, but an oral airway may still trigger a gag response and vomiting, risking aspiration. Although mask ventilation techniques emphasize jaw thrust, struggling to maintain upper airway patency in a supine position is intrinsically self-defeating. It is also ergonomically difficult and frequently a multi-person task, especially in large patients.