Mucus Plugging

Obstruction of segmental or larger airways by inspissated mucus that cannot be cleared, causing air trapping, atelectasis, recurrent infection and breathlessness.

• Settings: severe asthma (mucus plugs on CT in about half of patients with severe disease, and they predict a lower FEV1 and exacerbations), allergic bronchopulmonary aspergillosis, cystic fibrosis, bronchiectasis, chronic obstructive pulmonary disease, mechanical ventilation, after surgery, neuromuscular weakness, dehydration, and ciliary dyskinesia.
• Mechanism: goblet cell hyperplasia, overproduction of gel-forming mucins (MUC5AC), eosinophil and neutrophil derived DNA, and impaired ciliary and cough clearance create viscous plugs.
• Plugs may be low attenuation (usual) or high attenuation on CT (more than 70 Hounsfield units, typical of allergic fungal disease).

Productive or dry cough, expectoration of casts or plugs, wheeze, breathlessness, chest tightness, recurrent chest infection, haemoptysis.

• Sudden hypoxaemia with lobar collapse in ventilated patients.
• Signs: localised reduced breath sounds, crackles, wheeze, dullness (collapse).
• Underlying disease features: atopy, nasal polyps, eosinophilia (asthma and allergic bronchopulmonary aspergillosis), steatorrhoea and sinus disease (cystic fibrosis), chronic purulent sputum (bronchiectasis), neuromuscular weakness.
• Differential diagnosis: endobronchial tumour, foreign body, bronchial stenosis, aspirated food, blood clot, tracheobronchomalacia, pneumonia, bronchial atresia with mucocele.
• Complications: lobar collapse, hypoxaemia and respiratory failure, recurrent pneumonia, bronchiectasis, fixed airflow obstruction, mucoid impaction, and failed extubation.

Chest X-ray: tubular or branching (finger in glove) opacities, collapse, hyperinflation distal to a plug.

• High-resolution CT: mucus plugs in segmental airways, tree-in-bud, bronchiectasis (central in allergic bronchopulmonary aspergillosis); high-attenuation mucus (more than 70 Hounsfield units) strongly suggests fungal allergy.
• Bronchoscopy for failure of treatment, collapse or diagnosis, with culture (bacterial, mycobacterial, fungal) and cytology.
• Sputum: culture, acid-fast smear, Xpert MTB/RIF, eosinophil count, fungal culture.
• Blood: eosinophil count (more than 0.5 x 10^9/L suggests atopic disease), total IgE (more than 1000 IU/mL supports allergic bronchopulmonary aspergillosis), Aspergillus specific IgE and IgG, skin prick test; sweat chloride (more than 60 mmol/L supports cystic fibrosis); immunoglobulins.
• Spirometry with bronchodilator response; lung clearance index in cystic fibrosis.

Hydration: oral fluids 2 to 3 L daily if not restricted; humidified oxygen and heated humidification in ventilated patients.

• Airway clearance (twice to three times daily, 15 to 30 minutes): active cycle of breathing technique, oscillating positive expiratory pressure device, postural drainage, high-frequency chest wall oscillation; physiotherapist assessment.
• Mucoactive drugs:
  • Nebulised hypertonic saline 7% 4 mL twice daily after salbutamol 2.5 mg (to prevent bronchospasm); use 3% if intolerant. Effective in bronchiectasis and cystic fibrosis.
  • Carbocisteine 750 mg three times daily, reduced to 750 mg twice daily when improved (chronic obstructive pulmonary disease and bronchiectasis; caution in peptic ulcer).
  • Dornase alfa 2.5 mg nebulised once daily in cystic fibrosis only (avoid in non-cystic fibrosis bronchiectasis, where it worsens outcomes).
  • Inhaled mannitol 400 mg twice daily in bronchiectasis or cystic fibrosis after a passed tolerance test in the supervised setting.
  • N-acetylcysteine 600 mg orally daily, or 3 to 5 mL of 20% solution nebulised with salbutamol (evidence limited).
• Mechanical insufflation-exsufflation in weak patients (plus 40 to minus 40 cmH2O, 4 to 5 cycles of 5 breaths twice daily and with chest infections), with manual assisted cough.
• Bronchoscopy with saline lavage (10 to 20 mL aliquots, up to 100 to 200 mL in total) and suction, or cryo-extraction, for lobar collapse or respiratory failure not responding to 24 to 48 hours of medical measures; in ventilated patients, early.
• Asthma with mucus plugging: inhaled corticosteroid with long-acting beta agonist (budesonide-formoterol 160/4.5 micrograms, 2 puffs twice daily, plus 1 to 2 puffs as needed up to 12 puffs a day); for severe eosinophilic disease, mepolizumab 100 mg SC every 4 weeks or benralizumab 30 mg SC every 4 weeks for 3 doses then every 8 weeks; short course of prednisolone 40 mg daily for 5 days for exacerbations.
• Allergic bronchopulmonary aspergillosis: prednisolone 0.5 mg/kg daily for 2 weeks, then 0.5 mg/kg on alternate days for 6 to 8 weeks, then tapered by 5 to 10 mg every 2 weeks (total 3 to 5 months); add itraconazole 200 mg twice daily for 16 weeks for relapses or steroid dependence (check levels and liver tests); omalizumab 150 to 375 mg SC every 2 to 4 weeks by weight and IgE as an alternative.
• Infection: sputum-directed antibiotics; empirical co-amoxiclav 625 mg three times daily for 7 to 14 days (ciprofloxacin 500 mg twice daily when Pseudomonas is isolated).
• Cystic fibrosis: modulator therapy through a specialist centre; high-calorie diet and pancreatic enzymes.
• Special groups: children (chest physiotherapy by trained carers, 3% saline 4 mL nebulised twice daily); pregnancy (physiotherapy, hydration, hypertonic saline, prednisolone and inhaled corticosteroids are safe; avoid itraconazole); elderly (assisted cough, swallow assessment); ventilated (heated humidification, avoid dry gas, regular suction, early bronchoscopy); renal impairment (reduce N-acetylcysteine and avoid large saline volumes in fluid-restricted patients).
• Red flags: acute lobar collapse with hypoxaemia, massive haemoptysis, silent chest in asthma, rapid fall in FEV1, fever with a plug and distal infection, failed extubation.
• Follow-up: review at 4 to 6 weeks with spirometry and chest X-ray; repeat CT at 3 to 6 months for persisting plugs; total IgE at 6 to 8 weeks for allergic bronchopulmonary aspergillosis, then every 3 months for a year; yearly CT if bronchiectasis progresses.