Obstructive Airway Diseases

Asthma

Pathophysiology

•    Chronic airway eosinophilic inflammation, bronchial hyperresponsiveness

•    Variable, reversible airflow obstruction

Common triggers

•    Allergens (house dust mite, pollen, pet dander)

•    Cold air

•    Exercise

•    NSAIDs (aspirin-sensitive asthma)

•    Occupational exposures

Monitoring

•    Peak expiratory flow rate (PEFR): diurnal variability >20%

•    FeNO: elevated suggests eosinophilic inflammation

Acute severe asthma — "O SHIT ME"

•    O₂: maintain sats 94–98%

•    Salbutamol: nebulised or high-dose via MDI + spacer

•    Hydrocortisone IV or oral prednisolone

•    Ipratropium bromide nebulised (severe)

•    Theophylline IV (rarely, consider if poor response)

•    Mg²⁺ sulfate IV (for life-threatening or non-responding severe asthma)

•    Escalation: consider ICU, possible intubation

Chronic Obstructive Pulmonary Disease (COPD)

Pathophysiology

•    Chronic bronchitis ("blue bloater"): productive cough ≥3 months for ≥2 years

•    Emphysema ("pink puffer"): alveolar wall destruction → air trapping, hyperinflation

Key features

•    Irreversible airflow limitation (post-bronchodilator FEV1/FVC <0.7)

•    Hyperinflation on CXR (flattened diaphragm, increased retrosternal space)

Management

•    Smoking cessation → most effective

•    Bronchodilators:

o    SABA or SAMA for relief

o    LABA and/or LAMA for maintenance

o    ICS (in combination) if frequent exacerbations or high eosinophil count

•    Vaccinations: annual influenza, one-off pneumococcal

•    Pulmonary rehab

Chronic CO₂ retention

•    Use controlled oxygen therapy (e.g., 24–28% via Venturi mask)

•    Target SpO₂ 88–92%

Alpha-1 Antitrypsin Deficiency

Features

•    Early-onset panacinar emphysema, especially lower lobes

•    Associated liver disease: cirrhosis, hepatocellular carcinoma

•    Inheritance: autosomal recessive (PiZZ genotype most severe)

Management

•    Smoking cessation critical

•    IV augmentation therapy (purified A1AT) in some cases

Long-Term Oxygen Therapy (LTOT)

Indications

•    PaO₂ <7.3 kPa on room air

•    PaO₂ <8.0 kPa with complications (e.g., polycythaemia, pulmonary hypertension, peripheral oedema)

Administration

•    Minimum 15 hours per day, improves survival

Respiratory Failure

Type 1 (hypoxaemic)

•    PaO₂ <8 kPa, normal/low PaCO₂

•    Causes: pneumonia, pulmonary oedema, PE, ARDS, ILD

Type 2 (hypercapnic)

•    PaO₂ <8 kPa, PaCO₂ >6.5 kPa

•    Causes: COPD exacerbation, severe asthma, neuromuscular disease (e.g., Guillain–Barré), chest wall deformity

Ventilatory Support

Non-invasive ventilation (NIV)

•    Indicated in acute Type 2 RF with acidosis (e.g., pH <7.35, PaCO₂ >6.5)

•    Common in COPD exacerbations

Continuous positive airway pressure (CPAP)

•    First-line for obstructive sleep apnoea (OSA)

•    Also used in acute pulmonary oedema

Invasive mechanical ventilation

•    Indications:

o    Failure of NIV (worsening acidosis or consciousness)

o    Respiratory arrest

o    Severe hypoxaemia

Extra Revision Pearls

•    Asthma: diurnal variability, reversibility clue

•    COPD: no full reversibility; consider eosinophil count for ICS

•    A1AT deficiency: always think if young smoker with basal emphysema + liver disease

•    NIV: do not use if vomiting risk, reduced consciousness, copious secretions