Stridor

Introduction

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.

Aetiology

The most common causes of stridor can be differentiated by age group (Table 1).

Table 1. Common causes of stridor by age group

Clinical features

History

Typical symptoms of stridor include:¹

• Sore throat
• Difficulty breathing
• Noisy breathing*
• Drooling or inability to swallow saliva
• Dysphagia
• Voice change (aphasia/hoarse voice)
• Fever

Less common symptoms of stridor include:

• Weight loss
• Cough (typically presents with croup)

Other important areas to cover in the history include:

• Any history of foreign body ingestion (often seen in children – history from parents)
• Allergy history

*Stridor is not to be confused with ‘stertor/snoring’ – a low pitched sound, generally produced from obstruction of the nares or nasopharynx.²

Clinical examination

Stridor warrants a rapid A-E assessment, primarily focusing on assessment of the airway.⁴

Airway

By definition, the presence of stridor indicates a degree of airway compromise. Examination should focus on identifying features of airway compromise and potential underlying causes of stridor.

Inspection:

• Signs of cyanosis: indicative of significant airway compromise
• Position of the patient: patients may often sit in a ‘tripod’ position (sat forward, neck extended with their arms by their side to aid in breathing)⁵
• Evidence of angioedema: suggestive of an anaphylactic reaction
• Drooling: associated with epiglottitis
• Asymmetrical neck swelling: suggestive of deep neck space infection
• The floor of the mouth: inspect for evidence of swelling/angioedema and quinsy

Palpation:

• Pain on palpation
• Palpable neck swellings

Movement:

• Restricted neck movements: associated with deep neck space infection 
• Trismus: difficulty opening mouth typically associated with quinsy/deep neck space infection

Flexible nasendoscopy (FNE) may be performed by the ENT SHO or SpR as part of the A-E assessment in order to visualise the vocal cords and assess for evidence of swelling or a foreign body.

Breathing

Following a thorough airway assessment, the features of the patient’s breathing must be evaluated, including:

• Respiratory rate, oxygen saturation, respiratory effort (tracheal tug, sub-costal and intercostal recession)
• 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

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

Disability

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

Exposure

Finally, full ‘top-to-toe’ exposure of the patient is essential, evaluating the following:

• Evidence of anaphylaxis such as an urticarial rash or angioedema
• Potential allergens 

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

Investigations

Further investigations should be considered after the airway is secured.

Laboratory investigations

Relevant laboratory investigations in the context of stridor, include:

• Bloods: FBC, U&Es, CRP (infection)
• ABG: if concerns regarding oxygenation or respiratory failure

Imaging

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

Management

Specialists should be involved early in the management of stridor including ENT and critical care staff (e.g. anaesthetics).

Initial interventions

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)

Specialist interventions

The airway should be assessed by a specialist (e.g. anaesthetist or ENT doctor) to allow consideration of further interventions including:

• Endotracheal intubation
• 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.

Key points

• 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.

References

1. Sicari V, Zaboo C. Stridor. Updated in 2020. Available from [LINK]
2. Rose J. Acute Stridor in Children. Published in 2019. Available from [LINK]
3. Boardman SJ. Laryngomalacia. Last updated in 2019. Available from [LINK]
4. The American College of Surgeons. Advanced Trauma Life Support Course manual Tenth Edition. Published in 2018. Available from [LINK]
5. Mohamad N et al. Acute Stridor-Diagnostic Challenges in Different Age Groups Presented to the Emergency Department. Published in 2012. Available from [LINK]
6. Valman HB. Stridor. Published in 1981. Available from [LINK]
7. Brady MF, Burns B. Airway Obstruction. Updated in 2020. Available from [LINK]
8. Price TM, McCoy EP. Emergency front of neck access in airway management. Published in 2019. Available from [LINK]

Reviewer

Miss Eleanor Crossley

Otolaryngology Registrar

Editor

Hannah Thomas