Key Facts

Bronchodilators are the cornerstone of pharmacological management in obstructive airways disease. They work by relaxing bronchial smooth muscle through different mechanisms.

Epidemiology

Asthma affects approximately 5.4 million people in the UK, while COPD affects around 1.2 million diagnosed patients. Bronchodilators are among the most commonly prescribed medications in the NHS, with over 50 million inhaler prescriptions annually.

Aetiology

Bronchodilators target the reversible component of airway obstruction:

• Beta-2 agonists: Stimulate beta-2 adrenoceptors → increased cAMP → smooth muscle relaxation
• Antimuscarinics: Block M3 muscarinic receptors → reduce acetylcholine-mediated bronchoconstriction
• Methylxanthines: Phosphodiesterase inhibition → increased cAMP; also adenosine receptor antagonism

Pathophysiology

Airway narrowing in obstructive disease results from:

• Bronchial smooth muscle contraction (targeted by bronchodilators)
• Mucosal oedema and inflammation (targeted by corticosteroids)
• Mucus hypersecretion
• Airway remodelling (irreversible in COPD)

Beta-2 receptors are G-protein coupled receptors (Gs) that activate adenylyl cyclase. Chronic use leads to receptor downregulation (tachyphylaxis), particularly with regular SABA use.

Indications for Bronchodilator Use

• Acute asthma: Wheeze, dyspnoea, chest tightness, cough — SABA is first-line rescue therapy
• COPD: Progressive breathlessness, chronic cough, sputum production
• Acute exacerbation of COPD: Increased dyspnoea, purulent sputum, increased sputum volume

Red Flags Requiring Urgent Assessment

• Life-threatening asthma: Silent chest, cyanosis, bradycardia, hypotension, confusion, PEF <33%
• Near-fatal asthma: Raised PaCO2 and/or requiring mechanical ventilation
• Peak flow <50% predicted (severe), <33% predicted (life-threatening)
• Failure to respond to initial bronchodilator therapy
• SpO2 <92%

Side Effects to Recognise

• Beta-2 agonists: Fine tremor, tachycardia, palpitations, headache, hypokalaemia, hyperglycaemia
• Antimuscarinics: Dry mouth, urinary retention, constipation, raised intraocular pressure
• Theophylline toxicity: Nausea, vomiting, arrhythmias, seizures (at levels >20 mg/L)

Bedside

• Peak expiratory flow (PEF): Serial measurements, diurnal variation >20% suggests asthma
• Pulse oximetry: SpO2 target 94-98% (88-92% in COPD with hypercapnic risk)
• Inhaler technique assessment: Up to 90% of patients use inhalers incorrectly

Bloods

• U&Es: Monitor potassium (beta-2 agonists cause hypokalaemia)
• Theophylline level: Target 10-20 mg/L; check 4-6 hours post-dose (oral) or within 24 hours of IV loading
• ABG: In severe/life-threatening exacerbations — assess for type 1 or type 2 respiratory failure

Imaging

• CXR: Rule out pneumothorax, consolidation, pulmonary oedema
• HRCT: If bronchiectasis or interstitial lung disease suspected

Special Tests

• Spirometry: FEV1/FVC ratio, reversibility testing with 400mcg salbutamol
• FeNO (fractional exhaled nitric oxide): >40 ppb supports eosinophilic inflammation/asthma
• Bronchial challenge testing: Methacholine or mannitol provocation if diagnosis uncertain

Non-pharmacological

• Inhaler technique education — reassess at every consultation
• Smoking cessation (COPD)
• Personalised asthma action plan
• Pulmonary rehabilitation (COPD, MRC dyspnoea grade ≥3)

Pharmacological

Asthma (NICE NG80):

1. SABA PRN (salbutamol 100-200mcg)
2. Add low-dose ICS (beclometasone 200-400mcg/day)
3. Add LTRA (montelukast 10mg ON) or LABA
4. Increase ICS to medium dose or add LABA if not tried
5. Consider specialist referral, high-dose ICS, add-on therapy (tiotropium, theophylline)

COPD (NICE NG115):

• No asthmatic features: SABA/SAMA → LABA+LAMA
• Asthmatic features/steroid-responsive: SABA → LABA+ICS → LABA+LAMA+ICS (triple therapy)
• Roflumilast 500mcg OD — PDE4 inhibitor for severe COPD with frequent exacerbations

Acute settings:

• Nebulised salbutamol 5mg + ipratropium 500mcg
• IV aminophylline: Loading dose 5mg/kg over 20 min (omit if on oral theophylline), then 0.5mg/kg/hr
• IV magnesium sulphate 1.2-2g over 20 min in life-threatening asthma

Referral Criteria

• Failure to achieve control on step 3 therapy (asthma)
• Diagnostic uncertainty
• Frequent exacerbations despite optimal therapy
• Suspected occupational asthma

• Well-controlled asthma has an excellent prognosis; approximately 1,400 asthma deaths per year in the UK (many preventable)
• COPD: FEV1 decline approximately 30-60mL/year vs 25-30mL/year in healthy non-smokers
• BODE index predicts COPD mortality (BMI, Obstruction, Dyspnoea, Exercise capacity)
• Smoking cessation is the only intervention proven to reduce FEV1 decline in COPD
• Long-acting bronchodilators reduce exacerbation rates by approximately 20-25%

Key Drug Interactions

Inhaler Devices