Stridor is an externally audible, high-pitched sound caused by turbulent airflow due to obstruction of the upper respiratory tract (pharynx, larynx or trachea).1,2 It is a life-threatening emergency as there is potential for airway compromise and respiratory arrest.
The most common causes of stridor can be differentiated by age group (Table 1).
Table 1. Common causes of stridor by age group
No major causes
Laryngomalacia (most common) – a congenital abnormality of the laryngeal cartilage that predisposes to the airway collapsing in during the inspiratory phase of respiration3
Croup (viral laryngotracheobronchitis)
Quinsy (peritonsillar abscess)
Deep neck space infections – parapharyngeal, retropharyngeal, submandibular (Ludwig’s angina)
Auscultation: wheeze may be a sign of obstruction distal to the large bronchi and might be suggestive of possible anaphylaxis
Reduced air entry is also a concerning finding indicating significant airway compromise
Circulation may be assessed as follows:
Pulse: patients with stridor may be tachycardic due to the increased respiratory effort, hypoxia and anxiety. This can be further exacerbated by the administration of nebulised adrenaline (see below).
Blood pressure: hypotension may be suggestive of systemic vasodilation due to anaphylaxis or an infective cause
Consciousness – in the context of stridor, a patient’s consciousness level may be reduced secondary to hypoxia or hypercapnia. The AVPU scale can be used to assess the patient’s level of consciousness:
Alert: the patient is fully alert, although they may still be distress or dis-orientated
Verbal: the patient makes some kind of response when you talk to them (e.g. words, grunting)
Pain: the patient responds to a painful stimulus
Unresponsive: the Glasgow Coma Scale (GCS) can be used for a more detailed assessment of consciousness
Temperature: fever may indicate infectious cause
Finally, full ‘top-to-toe’ exposure of the patient is essential, evaluating the following:
Evidence of anaphylaxis such as an urticarial rash or angioedema
Classification of stridor
The character of the stridor gives an indication as to the location of the obstruction:
Inspiratory: obstruction above or at the level of the vocal cords (glottis or supraglottic)
Biphasic: obstruction below the vocal cords (subglottic)
Expiratory: obstruction of the trachea or larger bronchi 1,5,6
Further investigations should be considered after the airway is secured.
Relevant laboratory investigations in the context of stridor, include:
Bloods: FBC, U&Es, CRP (infection)
ABG: if concerns regarding oxygenation or respiratory failure
Relevant imaging in the context of stridor includes:
Flexible nasendoscopy (as above)
CT neck: although this is not an acute investigation, it may be performed if there is clinical suspicion of an abscess or malignancy7
Specialists should be involved early in the management of stridor including ENT and critical care staff (e.g. anaesthetics).
Whilst awaiting specialist input, a number of interventions can be considered to help stabilise the patient:
Sit patient upright
High flow O2 (humidified if possible)
Heliox (helium mixed with Oxygen) is sometimes used if available to help to reduce work of breathing
Nebulised adrenaline: assess response and repeat if necessary
IV high dose steroids (e.g. dexamethasone)
IV broad-spectrum antibiotics: if there is a suspicion of infection (consult local guidelines)
The airway should be assessed by a specialist (e.g. anaesthetist or ENT doctor) to allow consideration of further interventions including:
If intubation is not possible, a surgical airway may be necessary (e.g. tracheostomy, cricothyroidotomy)8
Once the airway is secured, further interventions to definitively treat the underlying cause will need to be considered.
Stridor can indicate life-threatening airway obstruction and requires urgent specialist assessment.
Patient age and symptom onset can help give an indication of the most likely aetiology.
Assessment of stridor includes a full A-E assessment +/- FNE.
Management may involve oxygen, adrenaline nebulisers, IV steroids, IV antibiotics and securing the airway (if necessary).
Early escalation to ENT and/or anaesthetic specialists is essential.
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Rose J. Acute Stridor in Children. Published in 2019. Available from [LINK]
Boardman SJ. Laryngomalacia. Last updated in 2019. Available from [LINK]
The American College of Surgeons. Advanced Trauma Life Support Course manual Tenth Edition. Published in 2018. Available from [LINK]
Mohamad N et al. Acute Stridor-Diagnostic Challenges in Different Age Groups Presented to the Emergency Department. Published in 2012. Available from [LINK]
Valman HB. Stridor. Published in 1981. Available from [LINK]
Brady MF, Burns B. Airway Obstruction. Updated in 2020. Available from [LINK]
Price TM, McCoy EP. Emergency front of neck access in airway management. Published in 2019. Available from [LINK]