2.1 Airway Anatomy & Assessment

Airway Anatomy & Assessment

A precise mental map of the airway is the foundation of every airway-management and oxygenation decision the respiratory therapist (RT) makes. The Therapist Multiple-Choice (TMC) Examination from the National Board for Respiratory Care (NBRC) — 160 items, 3 hours, 140 scored — repeatedly tests anatomy not as trivia but as the reasoning behind tube placement, suction depth, aspiration risk, and the urgent recognition of failing patients.

Upper Airway: The Conditioning Zone

The upper airway extends from the nose and mouth to the larynx and warms, filters, and humidifies inspired gas, delivering it to the carina at roughly 37 degrees C and 44 mg/L absolute humidity.

Lower Airway: The Conducting & Gas-Exchange Zone

The lower airway begins at the trachea (10-12 cm, C-shaped rings open posteriorly) and branches at the carina into the mainstem bronchi.

Worked trap: An intubated patient suddenly loses left-sided breath sounds with a rising peak pressure. Because the right mainstem is more vertical, the ETT has most likely migrated into the right mainstem. The fix is to deflate the cuff, withdraw the tube 1-2 cm, re-auscultate for bilateral sounds, re-inflate, and confirm by chest X-ray (tip 3-5 cm above the carina).

Distress Versus Impending Failure

The single most tested clinical judgment here is separating a compensating patient (distress) from a decompensating one (impending failure). Distress can often be managed with oxygen, bronchodilators, or noninvasive ventilation; impending failure demands an advanced airway.

Respiratory distress — the patient is still working effectively:

• Tachypnea (respiratory rate > 20/min in adults)
• Accessory muscle use (sternocleidomastoid, scalenes, intercostals)
• Nasal flaring; intercostal and suprasternal retractions
• Diaphoresis, agitation, inability to speak full sentences
• Tripod positioning (upright, leaning forward, arms braced)

Impending respiratory failure — the patient is losing the battle:

• Altered mental status (confusion, somnolence, unresponsiveness)
• Paradoxical (abdominal) breathing — abdomen sinks as the chest rises
• Bradycardia and a falling respiratory rate (ominous late signs)
• Central cyanosis of lips and mucous membranes
• Silent chest — no air movement despite visible effort

A classic exam scenario: a severe asthmatic who was loudly wheezing now has a quiet chest, a normalizing (no longer low) PaCO2, and is drowsy. This is not improvement — it is exhaustion and impending failure, and the answer is to prepare for intubation, not to celebrate.

Mallampati Classification

The Mallampati score predicts laryngoscopic difficulty from how much pharyngeal anatomy is visible with the mouth wide open and tongue protruded.

Mallampati is one of several difficult-airway predictors. Others worth recognizing include a thyromental distance under three fingerbreadths (a short, recessed chin), limited mouth opening under three fingerbreadths between the incisors, restricted neck extension, a large tongue or short muscular neck, and obstructive pathology such as airway burns, angioedema, or an expanding hematoma. A high Mallampati class is a flag, not a verdict: it tells the team to optimize positioning, have a video laryngoscope and a supraglottic rescue airway at the bedside, and avoid eliminating spontaneous ventilation until the airway is secured.

Positioning and Pediatric Differences

Proper positioning aligns the oral, pharyngeal, and laryngeal axes. In an adult, the sniffing position — neck flexed on the body with the head extended at the atlanto-occipital joint, often with a pad under the occiput — gives the best laryngoscopic view.

The pediatric airway differs in ways that change technique: the occiput is large (so a shoulder roll, not a head pad, achieves neutral alignment in infants), the tongue is proportionally larger, the larynx sits higher and more anterior (about C3-C4 versus C5-C6 in adults), the epiglottis is longer and floppier (favoring a straight Miller blade), and the cricoid ring is the narrowest point rather than the glottis. These differences explain why pediatric airway obstruction develops quickly and why even small amounts of edema or a slightly oversized tube cause disproportionate airway narrowing in a child.

Putting Assessment Together

Clinical assessment is a continuous loop, not a single snapshot. The RT integrates inspection (work of breathing, color, position, mentation), auscultation (air movement, adventitious sounds, symmetry), vital-sign trends, pulse oximetry, and — when available — arterial blood gases. A patient whose SpO2 holds but whose PaCO2 is climbing while alertness fades is heading toward ventilatory failure even with a 'normal' oxygen number, a pattern the exam uses to test whether you understand that oxygenation and ventilation are separate problems.