Airway Anatomy and Physiology Review

Overview

A clear understanding of airway anatomy and physiology is the foundation of safe respiratory therapy practice. Before you can manage, protect, or support a patient's airway, you must be able to picture every structure from the nose and mouth down to the alveoli — and recognize how those structures change across age groups and body types. Errors in airway management are among the most time-sensitive threats to patient safety, so accuracy here is not optional.

Upper Airway Structures

The upper airway begins at the nose and mouth and extends to the larynx. Key structures include:

• Nasal cavity and turbinates — warm, humidify, and filter inhaled air. The turbinates increase surface area for this conditioning function.
• Nasopharynx — the space behind the nasal cavity; contains the adenoids (lymphoid tissue) and the openings of the Eustachian tubes.
• Oropharynx — the space behind the mouth, extending from the soft palate to the epiglottis; the passage shared by food and air.
• Epiglottis — a leaf-shaped cartilage that folds over the glottis during swallowing to protect the lower airway from aspiration.
• Larynx — a cartilaginous structure housing the vocal cords (true vocal folds). Its components include the thyroid cartilage (the largest), the cricoid cartilage (the only complete ring), the arytenoid cartilages, and the cricothyroid membrane — a critical landmark for emergency surgical airway access.
• Glottis — the space between the true vocal cords; the narrowest part of the adult airway.

Lower Airway Structures

Below the larynx, the lower airway conducts and exchanges gas:

• Trachea — approximately 10–12 cm long in adults, supported by C-shaped cartilaginous rings with a posterior membranous wall abutting the esophagus.
• Carina — the ridge at the tracheal bifurcation, roughly at the level of the sternal angle (angle of Louis). Stimulation of the carina triggers a strong cough reflex.
• Main (primary) bronchi — the right mainstem bronchus is shorter, wider, and more vertical than the left, making it the more common site of foreign body aspiration and inadvertent intubation.
• Lobar (secondary) and segmental (tertiary) bronchi — branch progressively, delivering air to each lobe and bronchopulmonary segment.
• Bronchioles and terminal bronchioles — conducting airways that lack cartilage and depend on lung elastic recoil to stay open.
• Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli — the gas-exchange zone; adult lungs contain roughly 300 million alveoli with an enormous combined surface area.

Pediatric Airway Variations

The infant and pediatric airway differs from the adult airway in ways that directly affect management decisions:

1. Narrowest point is the subglottic region (at the cricoid ring), not the glottis as in adults — a critical reason why uncuffed or appropriately sized cuffed tubes are used cautiously in young children.

2. Larger relative tongue — occupies more of the oral cavity, increasing obstruction risk.

3. Omega-shaped, floppy epiglottis — less rigid; a straight laryngoscope blade is often preferred to lift it directly.

4. More anterior and cephalad larynx — the infant larynx sits at approximately C3–C4 compared with C5–C6 in adults, making visualization more challenging.

5. Smaller airway diameter — even a small amount of edema or secretions dramatically increases airway resistance (resistance increases as the radius decreases to the fourth power in laminar flow — Poiseuille's Law).

6. Shorter trachea — the risk of right mainstem intubation or accidental extubation during movement is higher.

Safety note: Always confirm pediatric tube size and depth against validated references and reassess with every position change.

Geriatric Airway Variations

Aging introduces anatomical and physiological changes that complicate airway management:

• Reduced atlantoaxial and cervical spine mobility — limits head extension needed for alignment during intubation; assume spinal fragility until evaluated.
• Loss of teeth or poorly fitting dentures — alters mask seal; dentures may be left in for bag-mask ventilation to maintain facial contour.
• Increased tissue fragility — mucous membranes tear easily; use lubricated, gentle technique.
• Decreased laryngeal reflexes — silent aspiration is more common; never assume the gag reflex reliably protects the airway.
• Reduced lung compliance and elastic recoil — higher risk of dynamic hyperinflation and air trapping.

Obese Patient Airway Considerations

Morbid obesity creates a distinct set of airway challenges:

• Excess soft tissue in the neck, tongue, and pharynx narrows the upper airway; obstructive sleep apnea is common.
• Difficult mask ventilation — adipose tissue limits seal; two-provider bag-mask technique is often required.
• Rapid oxygen desaturation — reduced functional residual capacity (FRC) means the oxygen reservoir in the lungs is smaller; preoxygenation with the patient in the ramped or head-elevated position is essential.
• Ramp positioning — aligning the external auditory meatus with the sternal notch (the "ramped" position) optimizes laryngoscopy view.
• Aspiration risk — increased intra-abdominal pressure raises the risk of regurgitation.

Safety note: For any high-risk airway, communicate findings clearly to the supervising physician or anesthesia provider and have backup equipment (video laryngoscope, supraglottic airway, surgical airway kit) immediately available.

Physiology Tie-In

The airway's primary physiological roles are gas conduction, conditioning (warming and humidifying air to 100% relative humidity at body temperature by the carina), and protection against aspiration and infection. Any structural change — whether developmental, pathological, or related to body habitus — can impair one or more of these functions. Your job as a respiratory therapist begins with recognizing these variations before you intervene.