Stridor

Stridor is a harsh, high pitched, musical sound produced by turbulent airflow through a narrowed upper airway (supraglottis, glottis, subglottis or trachea), most typically heard on inspiration. It includes the clinical presentation of noisy breathing. Stridor is a medical emergency until proved otherwise: it signals significant airway narrowing (often over 50%), and the airway can occlude suddenly.

Clinical relevance. Common causes in adults are:

• anaphylaxis and angioedema
• infection (epiglottitis, supraglottitis, retropharyngeal abscess, Ludwig angina)
• foreign body
• tumours (laryngeal, tracheal, thyroid, mediastinal)
• post intubation or tracheostomy stenosis
• vocal cord paralysis
• thermal or caustic injury
• trauma

In children, croup, laryngomalacia, foreign body and epiglottitis (now rare after vaccination) predominate. Biphasic or expiratory stridor suggests lower tracheal or fixed lesions. Stridor in an adult needs urgent airway assessment by an experienced clinician.

Classification.

• By phase: inspiratory (supraglottic or glottic lesion), biphasic (subglottic or glottic fixed obstruction, tracheal lesions), expiratory (lower tracheal or bronchial lesions; resembles wheeze).
• By level: supraglottic (epiglottitis, supraglottitis, laryngomalacia, cyst, tumour), glottic (vocal cord paralysis, laryngeal papillomatosis, oedema, web, foreign body), subglottic (croup, stenosis, haemangioma, post intubation granuloma), tracheal (stenosis, tracheomalacia, tumour, external compression, vascular ring, goitre).
• By onset: acute (minutes to hours: anaphylaxis, foreign body, epiglottitis, croup, burns), subacute (days: abscess, tumour, angioedema, laryngeal infection) and chronic (weeks to years: stenosis, tumour, vocal cord paralysis, laryngomalacia).
• By character: high pitched crowing (laryngeal), low pitched snoring (pharyngeal), fixed (does not change with position), positional.

Mechanism. Bernoulli effect and negative intrathoracic pressure during inspiration collapse a narrowed extrathoracic airway, increasing velocity and turbulence. Airway resistance rises as the fourth power of radius reduction, so a small further oedema can cause complete obstruction, especially in infants.

History (brief; never delay securing the airway).

• Onset (sudden or progressive), duration, progression, relation to meals, choking, trauma, burns, exposure to allergens (insect sting, food, drug), recent intubation or tracheostomy (granulation, stenosis), neck surgery (thyroidectomy: bleeding, recurrent laryngeal nerve palsy), radiotherapy, anticoagulation.
• Associated symptoms: voice change or hoarseness, dysphagia, odynophagia, drooling, sore throat, fever, neck swelling, cough, haemoptysis, weight loss, breathlessness, exercise limitation, orthopnoea, facial swelling, rash.
• Prior episodes (hereditary angioedema, croup), smoking and alcohol (laryngeal cancer), HIV, immunosuppression, tuberculosis, sarcoidosis, granulomatosis with polyangiitis (subglottic stenosis), relapsing polychondritis, reflux, goitre.
• Drugs: ACE inhibitors (angioedema), NSAIDs, new antibiotics.
• Children: age, vaccination, barking cough, fever, drooling, feeding, noisy breathing since birth or after URTI, prematurity and intubation.

Examination (while preparing to intervene).

• Look first, do not agitate the patient: position of comfort (sitting forward, tripod), drooling, cyanosis, distress, retraction (suprasternal, subcostal), stridor (loudness, phase, pitch), voice (muffled hot potato voice, hoarse, aphonic), cough (barking), ability to speak.
• Vital signs: respiratory rate, saturation (late sign), heart rate, blood pressure, temperature, mental state (hypoxia, hypercapnia).
• Neck: swelling, crepitus (surgical emphysema), mass, goitre, lymphadenopathy, scar, trachea position, tenderness over larynx.
• Mouth and throat only if safe (avoid in suspected epiglottitis in children): tonsils, uvula, floor of mouth, tongue and lip swelling, oropharyngeal abscess.
• Skin: urticaria, angioedema, burns, singed nasal hair, soot in sputum (inhalation injury).
• Chest: wheeze, reduced air entry, unilateral changes.
• Do not examine the throat with a spatula in a child with suspected epiglottitis.

Red flags.

• Stridor at rest, severe retraction, cyanosis, silent child or adult, exhaustion, agitation then drowsiness (impending complete obstruction).
• Drooling, tripod posture, muffled voice, fever and toxic appearance (epiglottitis, supraglottitis, abscess).
• Lip, tongue or facial swelling with urticaria or wheeze (anaphylaxis).
• Sudden onset with choking (foreign body).
• Burns to the face, singed nasal hair, soot, carbonaceous sputum, hoarse voice (inhalation injury; airway swelling may develop over hours).
• Neck trauma, expanding haematoma, surgical emphysema, post thyroidectomy swelling.
• Weight loss, haemoptysis, hoarseness over 3 weeks in a smoker (tumour).
• Progressive stridor with exertional breathlessness and a normal chest examination (tracheal stenosis).
• Bilateral vocal cord palsy (aphonia, stridor).

Infective and inflammatory. Epiglottitis and supraglottitis (Haemophilus influenzae type b, Streptococcus, Staphylococcus), croup (laryngotracheobronchitis, parainfluenza), bacterial tracheitis, peritonsillar abscess, retropharyngeal and parapharyngeal abscess, Ludwig angina, diphtheria, laryngeal tuberculosis, laryngeal candidiasis, infectious mononucleosis with tonsillar hypertrophy, laryngeal sarcoidosis, granulomatosis with polyangiitis, relapsing polychondritis, amyloidosis.

Allergic and angioedema. Anaphylaxis, ACE inhibitor angioedema, hereditary angioedema (C1 esterase inhibitor deficiency), acquired angioedema, allergic laryngeal oedema.

Obstruction and foreign body. Aspirated foreign body (laryngeal, tracheal), food bolus, vomit aspiration, dentures, blood clot.

Neoplastic and mass. Laryngeal carcinoma, papillomatosis, tracheal tumours (squamous, adenoid cystic), thyroid carcinoma or goitre (retrosternal), mediastinal masses (lymphoma, thymoma), oesophageal cancer, lung cancer with tracheal invasion, haemangioma (infants), cystic hygroma, vallecular cyst.

Neurological and functional. Vocal cord paralysis (unilateral or bilateral: thyroid surgery, cardiothoracic surgery, neck malignancy, stroke, Guillain-Barre syndrome, myasthenia, Parkinson disease and multiple system atrophy), vocal cord dysfunction (paradoxical vocal fold motion), laryngospasm (post extubation, reflux), hypocalcaemia (laryngospasm and tetany), bulbar disease.

Structural and congenital. Laryngomalacia (commonest cause of infantile stridor, often resolves by 18 months), subglottic stenosis (congenital and acquired post intubation), tracheomalacia, laryngeal web or cleft, vascular ring or sling, tracheo-oesophageal fistula, bronchogenic cyst, Pierre Robin sequence, macroglossia.

Traumatic and iatrogenic. Neck trauma and laryngeal fracture, post intubation or tracheostomy stenosis and granulomas, post thyroidectomy haematoma, caustic ingestion, thermal burns and smoke inhalation, radiation oedema, cuff overinflation, tracheo innominate fistula.

Metabolic and other. Hypocalcaemia, anaphylactoid reactions, obstructive sleep apnoea (mimics), high altitude, thyroid storm with compression.

1. Resuscitation and airway control come first. Do not send an unstable patient for scans. Call anaesthesia, ENT and critical care (the "difficult airway team") at once.
2. Bedside assessment: pulse oximetry, respiratory rate, blood pressure, temperature. Avoid distressing the child; allow position of comfort; avoid blind throat examination.
3. Flexible nasendoscopy (fibreoptic laryngoscopy) by ENT or anaesthetist is the key test. Perform it with the patient awake and the airway team ready. It shows epiglottis, supraglottis, cords (mobility), subglottis, pooled secretions, tumour, oedema, foreign body, web.
4. Imaging (only when stable, with airway support available):
   • Soft tissue lateral neck radiograph: thumb sign in epiglottitis, steeple sign on posteroanterior view in croup, prevertebral widening in retropharyngeal abscess.
   • Chest radiograph: foreign body, mediastinal mass, tracheal deviation, infiltrate.
   • CT neck and chest with contrast: abscess, tumour, stenosis, compression, vascular rings.
   • MRI for soft tissue and vascular lesions; barium swallow for vascular rings; dynamic airway CT for tracheomalacia.
5. Flow volume loop and spirometry once stable. Variable extrathoracic obstruction flattens the inspiratory limb; fixed obstruction flattens both limbs.
6. Blood tests:
   • Full blood count, C reactive protein, blood cultures, coagulation, arterial blood gas.
   • Calcium and magnesium (hypocalcaemia).
   • Mast cell tryptase (1 to 2 hours after anaphylaxis).
   • C4 and C1 esterase inhibitor level and function (hereditary angioedema; low C4 in attacks).
   • Thyroid function, antineutrophil cytoplasmic antibody, HIV, ACE inhibitor history.
7. Microbiology: throat and tracheal swabs, epiglottic swabs after the airway is secure.
8. Rigid or flexible bronchoscopy and microlaryngoscopy under anaesthesia for definitive diagnosis, biopsy and removal of foreign body or dilation; tracheal evaluation.
9. Voice and swallowing assessment (speech and language therapy) for vocal cord palsy and vocal cord dysfunction; thyroid and mediastinal evaluation.
10. Genetic and developmental assessment in infants (congenital anomalies, syndromes, neurological conditions).

Limits. Imaging in unstable patients is dangerous. Plain neck radiographs can be normal in early supraglottitis and abscess. Oximetry stays normal until late. Flexible endoscopy can precipitate obstruction if the airway is critical, so perform it in an environment ready for intubation or surgical airway.

Stridor may be absent in complete obstruction or exhaustion (ominous silence). Stridor in obesity and sleep apnoea may be hard to differentiate from snoring.

Immediate priorities (any patient with stridor).

• Call the airway team (senior anaesthetist, ENT surgeon, critical care) at once. Prepare for difficult airway: videolaryngoscopy, smaller tubes (5.0 to 6.0 mm), bougie, supraglottic airway, and front of neck access kit (scalpel, bougie, 6.0 tube) with an operator ready.
• Keep the patient calm and sitting upright. Avoid lying flat, agitation or unnecessary examination. Allow a parent to hold a child. Do not examine the throat or take blood if it will distress a child with suspected epiglottitis.
• High flow oxygen 15 L/min by non rebreather mask (blow by for children). Monitor continuously (saturation, ECG, blood pressure, capnography if intubated).
• Intravenous access (in a controlled setting); treat the cause immediately.
• Heliox (70% helium and 30% oxygen) as a temporary bridge to reduce turbulence and work of breathing in severe obstruction when available.
• Nebulised adrenaline 1:1,000: 5 mL (5 mg) in adults, 0.4 mL/kg (maximum 5 mL) in children. Repeat every 15 to 30 minutes with monitoring. Benefit is transient in croup, post extubation stridor, and upper airway oedema; watch for rebound.
• Dexamethasone 8 to 10 mg intravenously in adults (or hydrocortisone 200 mg) for oedema of infective, inflammatory or traumatic origin. For croup, 0.15 mg/kg oral or intramuscular (maximum 10 mg).
• Intubate early with experienced operators in theatre ("double set up" with surgeon ready to perform tracheostomy or cricothyroidotomy). Use inhalational induction maintaining spontaneous breathing where appropriate. Avoid paralysis until the airway is confirmed. If cannot intubate, cannot oxygenate, perform a surgical airway (scalpel cricothyroidotomy).

Anaphylaxis and angioedema.

• Adrenaline 0.5 mg (0.5 mL of 1:1,000) intramuscularly into the anterolateral thigh, repeated every 5 minutes if no improvement. Dose is 150 micrograms in children under 6 years and 300 micrograms at 6 to 12 years.
• Adjuncts: nebulised adrenaline 5 mg for upper airway oedema; high flow oxygen; 0.9% sodium chloride 500 to 1,000 mL; chlorphenamine 10 mg intravenously; hydrocortisone 200 mg intravenously; nebulised salbutamol 5 mg for wheeze.
• Adrenaline infusion for refractory shock; early intubation if stridor progresses.
• ACE inhibitor angioedema: stop the drug permanently (and avoid angiotensin receptor blockers initially). Secure airway early (fibreoptic intubation or awake tracheostomy). Icatibant 30 mg subcutaneously may help. Antihistamine and steroids are ineffective but often given.
• Hereditary angioedema:
  • C1 esterase inhibitor concentrate 20 units/kg intravenously (or 1,000 to 2,000 units), icatibant 30 mg subcutaneously (repeat every 6 hours, maximum 3 doses in 24 hours), or ecallantide.
  • Fresh frozen plasma 2 units if unavailable. Avoid adrenaline monotherapy as sole therapy.
  • Long term prophylaxis: lanadelumab 300 mg subcutaneously every 2 weeks, berotralstat 150 mg daily, or tranexamic acid and danazol in selected cases. Give short term prophylaxis before procedures.

Epiglottitis and supraglottitis, deep neck infections.

• Secure the airway first (in theatre), then ceftriaxone 2 g intravenously daily (50 to 100 mg/kg in children) or cefotaxime 2 g every 8 hours.
• Add flucloxacillin 2 g every 6 hours if staphylococcal infection is suspected (or vancomycin 15 to 20 mg/kg). Add metronidazole 500 mg every 8 hours for abscess.
• Give dexamethasone 8 mg intravenously. Drain abscess surgically.
• Rifampicin prophylaxis (20 mg/kg daily for 4 days) for household contacts of Haemophilus influenzae type b; vaccination review.
• Ludwig angina: airway control, high dose antibiotics (benzylpenicillin 1.2 g every 6 hours with metronidazole 500 mg every 8 hours, or co-amoxiclav 1.2 g every 8 hours), drainage.

Croup. Dexamethasone 0.15 mg/kg orally or intramuscularly once (up to 0.6 mg/kg for severe). Nebulised adrenaline 0.4 mL/kg of 1:1,000 (maximum 5 mL) for stridor at rest. Oxygen for hypoxia; heliox. Observe for 2 to 4 hours after adrenaline. Admit for stridor at rest, hypoxia or inadequate response. Intubate only if exhausted.

Foreign body.

• Complete obstruction in adults: five back blows then five abdominal thrusts (Heimlich), alternating. Use chest thrusts if pregnant or obese. For infants, five back blows and five chest thrusts. If unresponsive, start cardiopulmonary resuscitation and use laryngoscopy and Magill forceps.
• Partial obstruction with good air movement: encourage coughing; urgent bronchoscopy (rigid, under general anaesthesia) or laryngoscopic removal.

Burns and inhalation injury. Intubate early if hoarseness, stridor, oropharyngeal soot or swelling, or burns to the face and neck (before oedema progresses). Give 100% oxygen for carbon monoxide. Consider cyanide antidote hydroxocobalamin 5 g intravenously in suspected smoke cyanide toxicity with lactate over 10 mmol/L or shock. Burns unit care.

Neck haematoma after thyroid or neck surgery. Immediate bedside release of skin sutures and strap muscles to decompress, then urgent return to theatre. High flow oxygen; intubation may be hard.

Tumour. Dexamethasone 8 mg intravenously then 4 mg every 6 to 8 hours, nebulised adrenaline, urgent ENT or thoracic assessment, tracheal stent, debulking or tracheostomy under local anaesthesia. Then oncology (radiotherapy, chemotherapy, resection). Laryngeal cancer needs urgent staging and treatment.

Vocal cord paralysis. Bilateral palsy with stridor: tracheostomy or cordotomy and arytenoidectomy. Unilateral: speech therapy and medialisation. Identify the cause (thyroid or mediastinal disease, stroke, neurological disease).

Tracheal stenosis or tracheomalacia. Bronchoscopic dilatation, laser, steroid injection (triamcinolone 40 mg), mitomycin C, stent, or resection with end to end anastomosis. Treat the cause (granulomatosis with polyangiitis: prednisolone 1 mg/kg with rituximab; relapsing polychondritis: prednisolone and immunosuppression).

Hypocalcaemia. Calcium gluconate 10% 10 to 20 mL (2.25 to 4.5 mmol) intravenously over 10 minutes, then infusion 100 mL of 10% in 1 litre of dextrose 5% at 50 to 100 mL/hour. Check magnesium (magnesium sulphate 2 g intravenously). Then oral calcium and calcitriol or alfacalcidol 0.25 to 1 microgram daily.

Vocal cord dysfunction. Reassure; coach "sniff" and relaxed throat breathing during an episode; speech and language therapy for long term control. Treat reflux (omeprazole 20 to 40 mg daily), rhinitis, anxiety (cognitive behavioural therapy). Avoid repeated steroids and unnecessary intubation.

Laryngomalacia and other infant causes. Observation if mild (feeding advice, reflux treatment with omeprazole 1 mg/kg daily when reflux). Supraglottoplasty for severe cases (failure to thrive, apnoea, cyanosis). Vascular rings need surgery.

Disposition.

• Resuscitation area then theatre or critical care for any patient with stridor at rest, rapid progression, hypoxia, drooling or distress. Keep in a monitored area; do not discharge until the airway is secure and the cause treated.
• Observation: croup mild, post adrenaline for at least 4 hours; mild allergic reactions at least 6 to 12 hours (biphasic reactions).
• Admit: all adults with new stridor, children with moderate to severe croup, epiglottitis, abscess, foreign body, burns, angioedema, tumours, post intubation stridor.
• Outpatient (urgent ENT clinic within 2 weeks): chronic, stable stridor with mild symptoms and good airway reserve, or hoarseness over 3 weeks.

Monitoring. Continuous oxygen saturation, respiratory rate, heart rate, blood pressure, work of breathing, voice, drooling, and capnography. Reassess after each intervention (adrenaline, steroid) and watch for rebound after 1 to 2 hours. After extubation observe 24 hours (cuff leak test before extubation in suspected oedema). Serial neck examination for haematoma; fibreoptic review of cord function.

Referral and escalation. ENT and anaesthesia (difficult airway) immediately; critical care; paediatric ENT and paediatric intensive care for children; thoracic surgery and interventional bronchoscopy for tracheal lesions; allergy and immunology for angioedema; infectious diseases for diphtheria and complex infection; oncology for tumours; speech and language therapy; endocrine surgery for thyroid causes; plastic surgery and burns unit for burns.

Safety netting. Return by emergency services for noisy breathing at rest, difficulty speaking, drooling, swelling of the lips, tongue or face, blue lips, choking, severe neck swelling, or worsening hoarseness. Carry the adrenaline auto-injector if prescribed, avoid known triggers, and wear an identification for hereditary angioedema. Keep follow up for persistent hoarseness over 3 weeks in smokers.

Special groups.

• Infants and children: croup, epiglottitis (rare, vaccination), laryngomalacia, foreign body, subglottic haemangioma (propranolol 1 mg/kg/day increasing to 2 to 3 mg/kg/day), vascular rings, post intubation stenosis. Small airway calibre means 1 mm of oedema reduces the area by 75%. Avoid agitation.
• Pregnancy: anaphylaxis (adrenaline is essential), laryngeal oedema in pre-eclampsia. Airway management is harder (oedema, aspiration risk); left lateral tilt.
• Older adults: tumour, vocal cord paralysis, ACE inhibitor angioedema, aspiration, reduced reserve.
• Immunosuppressed: candidiasis, cytomegalovirus, herpes, tuberculosis and aggressive infection.
• Surgical patients: early postoperative haematoma, recurrent laryngeal nerve injury, post extubation stridor (risk factors include prolonged intubation over 36 hours, large tube, trauma).
• Endemic regions: consider diphtheria (membrane, bull neck, antitoxin 20,000 to 100,000 units intravenously with benzylpenicillin or erythromycin), tuberculosis, rabies (laryngospasm), tetanus (laryngospasm), snake venom and caustic ingestion.