Upper airway obstruction (UAO) is a serious medical condition defined as a blockage of the air passage above the thoracic inlet, encompassing the pharynx, larynx, and upper trachea. This restriction of airflow often produces a characteristic high-pitched sound called stridor, which is typically heard upon inhalation. The severity of the obstruction can range from mild to life-threatening, and because it can rapidly lead to respiratory failure, UAO is considered a medical emergency requiring immediate attention. The specific diagnosis determines the cause of the blockage, which can be broadly categorized into acute infectious, acute non-infectious, and chronic progressive conditions.
Acute Infectious Conditions
Infectious causes frequently trigger acute upper airway obstruction, especially in children, due to the smaller diameter of their airways. Croup is one of the most common infectious diagnoses, resulting from a viral infection, most often parainfluenza virus. This infection causes inflammation and swelling in the subglottic region, leading to the hallmark symptom of a distinctive “seal-like” or “barking” cough. Although Croup is typically self-limited, the narrowed airway space exponentially increases the work of breathing.
A more severe, though now rarer, bacterial infection is Epiglottitis, which causes rapid and substantial swelling of the epiglottis. The swollen epiglottis can obstruct the airway quickly, causing patients to present with a sudden high fever, drooling, difficulty swallowing, and a muffled voice. Because examining the throat in a patient suspected of having Epiglottitis can trigger complete airway collapse, a high degree of clinical suspicion is necessary to avoid unnecessary manipulation.
Other infectious conditions that cause UAO through mass effect are deep neck space infections like Peritonsillar Abscess and Retropharyngeal Abscess. A Peritonsillar Abscess is a collection of pus typically behind the tonsil, most common in adolescents and young adults, which can cause obstruction due to localized swelling and uvular deviation. Retropharyngeal Abscesses are less common but particularly dangerous, occurring in the space behind the pharynx, primarily in young children under the age of five, where the enlarging abscess can directly compress the airway.
Acute Non-Infectious Events
Upper airway obstruction can also result from sudden physical or inflammatory events unrelated to infection. Foreign Body Aspiration is a common acute event, especially in toddlers between one and three years old who inhale small objects or food into the airway. If the object lodges in the larynx or upper trachea, it can cause immediate and life-threatening obstruction, presenting with sudden choking, coughing, and stridor. The severity depends on the size and location of the object, which can vary from a partial to a complete blockage.
Inflammatory swelling from a severe allergic reaction, known as Anaphylaxis, can rapidly compromise the airway. This reaction involves the release of massive amounts of inflammatory mediators, such as histamine, which cause the tissues of the larynx and pharynx to swell dramatically. Similarly, Angioedema, which is characterized by swelling of the skin and mucosal layers, can also cause life-threatening upper airway swelling. Angioedema may be histamine-mediated, similar to an allergic reaction, or bradykinin-mediated, often seen in hereditary forms or as a side effect of certain blood pressure medications.
Chronic Structural and Progressive Diagnoses
Conditions that cause gradual or long-term narrowing are categorized as chronic structural and progressive diagnoses. Laryngomalacia is the most frequent congenital cause of stridor in infants, resulting from immature, soft laryngeal cartilage that collapses inward during inspiration. This dynamic collapse of the supraglottic structures results in a high-pitched inspiratory stridor that is often worse when the infant is feeding or lying on their back. In most cases, symptoms are mild and resolve spontaneously as the cartilage matures, typically by 18 to 24 months of age.
Another structural diagnosis is Subglottic Stenosis, defined as a narrowing of the airway just below the vocal cords at the level of the cricoid cartilage. This stenosis can be congenital, due to a malformation of the cricoid cartilage during embryonic development, or acquired. The acquired form is most commonly caused by scarring from mechanical trauma, particularly prolonged endotracheal intubation, where the pressure of the breathing tube causes tissue necrosis and subsequent scar formation.
Progressive obstruction can also be caused by Tumors and other masses within the airway. Benign growths, such as recurrent respiratory papillomatosis (RRP), are caused by the human papillomavirus (HPV) and present as warty growths, primarily on the vocal cords and larynx. These papillomas can proliferate, leading to progressive hoarseness and airway narrowing that requires repeated surgical removal. Malignant tumors, such as laryngeal or tracheal cancers, cause progressive obstruction as the mass grows into the airway lumen or compresses it from the outside.
Recognizing Signs of Severe Obstruction
Recognizing the signs of severe airway obstruction is paramount, as the patient’s condition can deteriorate rapidly. A patient in distress may exhibit stridor that is audible even when they are resting. Increased work of breathing is evident through the use of accessory muscles, including nasal flaring and noticeable inward pulling of the skin between the ribs and at the base of the neck, known as retractions.
A change in mental status, such as agitation or lethargy, is a grave sign indicating poor oxygenation of the brain. If the obstruction is nearly complete, the patient may be unable to speak, cry, or cough. Their skin, lips, or nail beds may take on a bluish or grayish color (cyanosis) due to a lack of oxygen, warranting immediate activation of emergency medical services and transport to a hospital emergency department.