Stridor: A Merck Manual of Patient Symptoms podcast
Stridor is a high-pitched, predominantly inspiratory sound. It is most commonly associated with acute disorders, such as foreign body aspiration but can be due to more chronic disorders, such as tracheomalacia.
Stridor is produced by the rapid, turbulent flow of air through a narrowed or partially obstructed segment of the extrathoracic upper airway. Involved areas include the pharynx, epiglottis, larynx, and the extrathoracic trachea.
Most causes manifest acutely, but some patients present with chronic or recurrent symptoms (see Table 8: Symptoms of Pulmonary Disorders: Some Causes of Stridor).
Acute causes are usually infectious except for foreign body and allergy. Chronic causes are usually a congenital or acquired structural abnormality of the upper airway.
The most common causes of acute stridor in children include
Epiglottitis has historically been a common cause of stridor in children, but its incidence has decreased since the introduction of the Haemophilus influenzae type B (HiB) vaccine. Various congenital airway disorders can manifest as recurrent stridor in neonates and infants.
Common causes in adults include
Vocal cord dysfunction often mimics asthma, so many patients with vocal cord dysfunction are incorrectly given drugs for asthma but do not respond. Epiglottitis may be becoming more common among adults, but adults with epiglottitis are less likely than children to have stridor.
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History of present illness should first identify whether symptoms are acute or chronic. If acute, any symptoms of URI (runny nose, fever, sore throat) or allergy (itching, sneezing, facial swelling, rash, potential allergen exposure) are noted. Recent intubation or neck surgery should be clinically obvious. If chronic, the age at onset (eg, since birth, since infancy, only in adulthood) and duration are determined, as well as whether symptoms are continuous or intermittent. For intermittent symptoms, provoking or exacerbating factors (eg, position, allergen exposure, cold, anxiety, feeding, crying) are sought. Important associated symptoms in all cases include cough, pain, drooling, respiratory distress, cyanosis, and difficulty feeding.
Review of systems should seek symptoms suggesting causative disorders, including heartburn or other reflux symptoms (laryngospasm); night sweats, weight loss, and fatigue (cancer); and voice change, trouble swallowing, and recurrent aspiration (neurologic disorders).
Past medical history in children should cover perinatal history, particularly regarding need for endotracheal intubation, presence of known congenital anomalies, and vaccination history (particularly HiB). In adults, history of prior endotracheal intubation, tracheotomy, recurrent respiratory infections, and tobacco and alcohol use should be elicited.
The first step is to determine the presence and degree of respiratory distress by evaluating vital signs (including pulse oximetry) and doing a quick examination. Signs of severe distress include cyanosis, decreased level of consciousness, low O2 saturation (eg, < 90%), air hunger, use of accessory inspiratory muscles, and difficulty speaking. Children with epiglottitis may sit upright with arms braced on the legs or examination table, lean forward, and hyperextend the neck with the jaw thrust forward and mouth open in an effort to enhance air exchange (tripod position). Moderate distress is indicated by tachypnea, use of accessory muscles of respiration, and intercostal retractions. If distress is severe, further examination is deferred until equipment and personnel are arranged for emergency management of the airway.
Oropharyngeal examination of a patient (particularly a child) with epiglottitis may provoke anxiety, leading to functional obstruction and loss of the airway. Thus, if epiglottitis is suspected, a tongue depressor or other instrument should not be placed in the mouth. When suspicion is low and patients are in no distress, they may undergo imaging; others should be sent to the operating room for direct laryngoscopy, which should be done by an otolaryngologist with the patient under anesthesia.
If the patient's vital signs and airway are stable and acute epiglottitis is not suspected, the oral cavity should be thoroughly examined for pooled secretions, hypertrophic tonsils, induration, erythema, or foreign bodies. The neck is palpated for masses and tracheal deviation. Careful auscultation of the nose, oropharynx, neck, and chest may help discern the location of the stridor. Infants should be examined with special attention to craniofacial morphology (looking for signs of congenital malformations), patency of the nares, and cutaneous abnormalities.
The following findings are of particular concern:
Interpretation of findings:
The distinction between acute and chronic stridor is important. Other clinical findings are also often helpful (see Table 8: Symptoms of Pulmonary Disorders: Some Causes of Stridor).
Acute manifestations are more likely to reflect an immediately life-threatening disorder. With these disorders, fever indicates infection. Fever plus barking cough suggests croup or, very rarely, tracheitis. Patients with croup typically have more prominent URI symptoms and less of a toxic appearance. Fever without cough, particularly if accompanied by toxic appearance, sore throat, difficulty swallowing, or respiratory distress, suggests epiglottitis and, in young children, the less common retropharyngeal abscess. Drooling and the tripod position are suggestive of epiglottitis, whereas retropharyngeal abscess may manifest with neck stiffness and inability to extend the neck.
Patients without fever or URI symptoms may have an acute allergic reaction or aspirated foreign body. Acute allergic reaction severe enough to cause stridor usually has other manifestations of airway edema (eg, oral or facial edema, wheezing) or anaphylaxis (itching, urticaria). Foreign body obstruction of the upper airway that causes stridor is always acute but may be occult in toddlers (older children and adults can communicate the event unless there is near-complete airway obstruction, which will manifest as such, not as stridor). Cough is often present with foreign body but rare with allergic reaction.
Chronic stridor that begins early in childhood and without a clear inciting factor suggests a congenital anomaly or an upper airway tumor. In adults, heavy smoking and alcohol use should raise suspicion of laryngeal cancer. Vocal cord paralysis usually has a clear precipitant, such as surgery or intubation, or is associated with other neurologic findings, such as muscle weakness. Patients with tracheomalacia frequently have cough productive of sputum and have a history of recurrent respiratory infections.
Testing should include pulse oximetry. In patients with minimal respiratory distress, soft-tissue neck x-rays may help. An enlarged epiglottis or retropharyngeal space can be seen on the lateral view, and the subepiglottic narrowing of croup (steeple sign) may be seen on the anteroposterior view. X-rays may also identify foreign objects in the neck or chest.
In other cases, direct laryngoscopy can detect vocal cord abnormalities, structural abnormalities, and tumors. CT of the neck and chest should be done if there is concern about a structural abnormality, such as an upper airway tumor or tracheomalacia. Flow-volume loops can be useful in chronic and intermittent stridor to show the presence of an upper airway obstruction. Abnormal flow-volume loop findings generally require follow up with CT or laryngoscopy.
Definitive treatment of stridor involves treating the underlying disorder. As a temporizing measure in patients with severe distress, a mixture of helium and O2 (heliox) improves airflow and reduces stridor in disorders of the large airways, such as postextubation laryngeal edema, croup, and laryngeal tumors. The mechanism of action is thought to be reduced flow turbulence as a result of lower density of helium compared with O2 and nitrogen.
Nebulized racemic epinephrine (0.5 to 0.75 mL of 2.25% racemic epinephrine added to 2.5 to 3 mL of normal saline) and dexamethasone (10 mg IV, then 4 mg IV q 6 h) may be helpful in patients in whom airway edema is the cause.
Endotracheal intubation should be used to secure the airway in patients with advanced respiratory distress, impending loss of airway, or decreased level of consciousness. When significant edema is present, endotracheal intubation can be difficult, and emergency surgical airway measures (eg, cricothyrotomy, tracheostomy) may be required.
Last full review/revision July 2012 by Noah Lechtzin, MD, MHS
Content last modified July 2012