upper airway obstruction
Summary
Upper airway obstruction refers to blockage of airflow anywhere from the nose/mouth through the larynx to the extrathoracic trachea, presenting classically with stridor (typically inspiratory), dyspnea, and use of accessory muscles. Common causes include foreign body aspiration, epiglottitis, croup, anaphylaxis, angioedema, and tumors. It is a medical emergency that can rapidly progress to complete obstruction and respiratory arrest.
Detail
Upper airway obstruction (UAO) involves narrowing or blockage of the airway proximal to the thoracic inlet, encompassing the nasal passages, oropharynx, larynx, and extrathoracic trachea. Because this region is extrathoracic, obstruction here classically causes inspiratory stridor: during inspiration, negative intrathoracic (and extrathoracic airway) pressure causes the flexible extrathoracic airway to collapse further at the site of obstruction, whereas expiration tends to push air through more easily. This contrasts with lower/intrathoracic airway obstruction (e.g., asthma), which causes expiratory wheezing because forced expiration increases pleural pressure and compresses the intrathoracic airways.
Etiologies span acute and chronic causes: - Infectious: epiglottitis (Haemophilus influenzae type b, especially unvaccinated children; "thumbprint sign" on lateral neck X-ray, muffled voice, tripod positioning), croup/laryngotracheobronchitis (parainfluenza virus, "steeple sign," barky cough), retropharyngeal abscess, peritonsillar abscess ("hot potato" voice, uvular deviation), bacterial tracheitis. - Allergic/immunologic: anaphylaxis (laryngeal edema), angioedema (ACE inhibitor-induced, hereditary angioedema due to C1 esterase inhibitor deficiency). - Mechanical/foreign body: aspirated foreign body (common in toddlers), food bolus impaction. - Traumatic: laryngeal fracture, inhalation burns, post-intubation stenosis. - Neoplastic: laryngeal carcinoma, thyroid mass compressing trachea. - Neuromuscular: vocal cord paralysis (bilateral), obstructive sleep apnea (functional collapse during sleep). - Congenital: laryngomalacia, choanal atresia, vascular rings.
Clinical presentation includes stridor, dyspnea, tachypnea, use of accessory respiratory muscles, cyanosis in severe cases, and in complete obstruction, inability to speak or cough (choking sign) with rapid progression to hypoxia and cardiac arrest if untreated.
Diagnosis is largely clinical; imaging (lateral neck X-ray, CT) and direct/flexible laryngoscopy help identify the cause once the airway is stabilized. Pulmonary function tests, if performed in stable patients, may show a plateau in both inspiratory and expiratory flow-volume loops (fixed obstruction) or selective flattening of the inspiratory limb (variable extrathoracic obstruction).
Management is guided by severity and cause: immediate airway stabilization (positioning, heliox, racemic epinephrine, nebulized epinephrine for croup, corticosteroids), definitive airway control via endotracheal intubation or emergent tracheostomy/cricothyrotomy if intubation fails, and treatment of the underlying cause (antibiotics for epiglottitis, epinephrine/antihistamines/steroids for anaphylaxis, removal of foreign body via Heimlich maneuver or bronchoscopy).
High-yield boards points: differentiate inspiratory stridor (upper/extrathoracic) from expiratory wheeze (lower/intrathoracic); epiglottitis vs. croup distinguishing features; recognize angioedema as a cause requiring urgent airway management; understand flow-volume loop patterns for fixed vs. variable obstruction.
Sources
- First Aid for the USMLE Step 1
- Harrison's Principles of Internal Medicine
- UpToDate: Upper airway obstruction in adults/children
- Robbins and Cotran Pathologic Basis of Disease
- Tintinalli's Emergency Medicine
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.