Definition

• Stridor is a symptom not a diagnosis and it is important to find the underlying cause.
• Stridor is a loud, harsh, high pitched respiratory sound. It may start as low-pitched 'croaking' and progress to high-pitched 'crowing' on more vigorous respiration.
• It is usually heard on inspiration due to partial obstruction of the airway (usually extrathoracic - that is, in the trachea, larynx or pharynx).
• Stridor can occur on expiration in severe upper airway obstruction but usually indicates tracheal or bronchial obstruction (intrathoracic).
• Biphasic stridor suggests subglottic or glottic obstruction.¹

Epidemiology

The detailed epidemiology of stridor depends on the cause, but it is worth noting the following patterns of disease:

• Stridor is common in younger children with smaller airways.
• In children, acute stridor often accompanies upper respiratory tract infection.
• In children, chronic stridor usually occurs with congenital conditions.
• Stridor in adults is much less common.
• Chronic stridor in adults often indicates serious underlying pathology.

Causes of stridor

The Venturi principle dictates that when a gas moves forward the lateral pressure drops. The lateral pressure is helping to hold open the airway and, when this pressure falls, the narrowed flexible airway (particularly so in children) collapses to obstruct airflow and generate the noise characteristic of stridor. Conditions causing stridor may involve the central nervous, cardiovascular, gastrointestinal and respiratory systems.

Causes of stridor in children

These may be acute or chronic and the presentation and causes are considered in the boxes below.²

Acute stridor in children

Chronic stridor in children

Causes of stridor in adults

These may again be acute or chronic but the likely causes differ in adults. The presentation and causes are considered in the boxes below.

Acute stridor in adults

Chronic stridor in adults

Presentation

A careful history gives helpful clues as to the aetiological cause of the stridor. Examination may occasionally help confirm the diagnosis. It is important to consider the age of the patients and whether the stridor is acute or chronic.

• History:
  • Children:
    • Age of onset.
    • Duration, progression and severity of stridor.
    • Precipitating factors (feeding, crying).
    • Whether positional (worse right/left, prone/supine).
    • Whether aphonia is present.
    • Other symptoms (cough, aspiration, drooling, choking, cyanosis, sleep).
    • Severity (colour change, respiratory effort, apnoea).
    • Perinatal history.
    • Developmental history.
    • Vaccination history.
    • Growth and weight gain.
  • Adults:
    • Onset, duration, progression and severity should all be assessed.
    • Past medical history and details of any trauma or surgery.
• Examination:
  • Consider:
    • It may be possible in both adults and children to elicit signs of the level at which airway narrowing is occurring.
    • If the patient is distressed, defer further examination until equipment and facilities are available for emergency airway management in children and adults.
    • Patients suspected particularly of having acute epiglottitis should not be examined.
  • Observe:
    • Fever and signs of toxicity suggesting bacterial infection.
    • Drooling from the mouth.
    • Character of cry, cough and voice.
    • In children, the craniofacial features, nasal patency and any cutaneous haemangiomas.
    • Any positional preference that alleviates stridor.
  • Palpate (very carefully):
    • Crepitations or masses in the neck, face or chest.
    • Deviation of the trachea.
  • Auscultate:
    • Nose, oropharynx, neck and chest (this can help locate the source of the stridor).

Differential diagnosis

Diagnosis is made from the list of causes above. It is useful to consider the likely and important diagnoses according to age:

• In neonates, consider particularly congenital laryngeal paralysis or choanal atresia.
• In children, consider inhaled foreign bodies (such as toys or peanuts), croup, acute epiglottitis, diphtheria, upper airway burns and anaphylaxis.
• In adults, consider anaphalaxis, thyroid disease, trauma and tumours. However, remember acute epiglottitis as this occurs in adults and requires prompt and appropriate management. Rarely, psychogenic stridor in young women.³

There is a clear distinction to be made between acute and chronic stridor. Some causes of stridor are life-threatening and need quick diagnosis and treatment.

Investigations

Mild stridor may require no investigation when self-limiting upper respiratory infections are the cause. The need for further investigation is dictated by the clinical situation, the degree of distress and the severity of the stridor. The following may be useful:

• Pulse oximetry.
• Arterial blood gases.
• Imaging:
  • AP and lateral X-rays of the neck and chest (can identify particularly epiglottitis).
  • Special view X-rays (inspiratory/expiratory and lateral decubitus X-rays to demonstrate air trapping).
  • Contrast studies (if compression, tracheoesophageal fistula, gastrooesophageal reflux suspected).
  • CT scanning (for aberrant vessels and mediastinal masses).
  • MRI scanning (particularly for upper airway and vascular abnormalities).
  • Virtual bronchoscopy.⁴
• Other tests and procedures:
  • Pulmonary function tests (differentiating restrictive/obstructive lesions and upper/lower airway obstruction).
  • Laryngoscopy and bronchoscopy (after oxygen saturations stable and acute epiglottitis excluded).

Management

This depends on the cause of the stridor. Management of the particular causes may be very different. However, the following general points can be made:

• Emergency management is essentially about maintainance of the airway. Ill patients (moderate-to-severe stridor) should be kept nil by mouth.
• If management of the airway fails, resuscitation procedures should be followed.
  

  In the event of cessation of stridor with airway obstruction: Abrupt cessation of stridor may herald complete obstruction with chest movement but no breath sounds. Patients will soon become unconscious. If there are any signs of airway obstruction from a suspected foreign body, try to clear this with back blows or abdominal thrusts (clearly not appropriate in acute epiglottitis). Give oxygen. If necessary, perform emergency endotracheal intubation, cricothyroidotomy or tracheostomy with mechanical ventilation. Be prepared to suction any aspirated vomit or blood through the endotracheal or tracheostomy tube.

• Medication from corticosteroids to antibiotics can be useful.
• A variety of surgical procedures may be necessary from tracheotomy to removal of obstructing tumours.

Document references

1. Spencer S, Yeoh BH, Van Asperen PP, et al; Biphasic stridor in infancy. Med J Aust. 2004 Apr 5;180(7):347-9.
2. Sherrington CA, Crameri JA, Coleman LT, et al; Stridor in an infant. Eur Respir J. 1999 Sep;14(3):717-9.
3. Wareing MJ, Mitchell D; Psychogenic stridor: diagnosis and management. J Accid Emerg Med. 1997 Sep;14(5):330-2. [abstract]
4. Seam N, Finkelstein SE, Gonzales DA, et al; The workup of stridor: virtual bronchoscopy as a complementary technique in the diagnosis of subglottic stenosis. Respir Care. 2007 Mar;52(3):337-9.

Internet and further reading

• Valman HB; ABC of 1 to 7. Stridor. Br Med J (Clin Res Ed). 1981 Jul 25;283(6286):294-5.

Acknowledgements