Acute respiratory distress syndrome (ARDS) is a form of non-cardiogenic respiratory failure caused by widespread inflammation and alveolar–capillary membrane damage. Understanding its pathophysiology, clinical features, and management is essential for recognising severe respiratory deterioration and guiding supportive care.

Interstitial lung disease (ILD) is a group of disorders marked by inflammation and fibrosis of the lung interstitium, leading to stiff, non-compliant lungs and impaired gas exchange. Understanding ILD is important because progressive thickening of the alveolar–capillary membrane increases the work of breathing, causes exertional hypoxaemia, and can ultimately lead to respiratory failure and pulmonary hypertension.

Pulmonary embolism (PE) is a condition in which a blood clot, usually originating from the deep veins of the legs, lodges in the pulmonary arterial circulation and abruptly obstructs blood flow through the lungs. Understanding PE is critical because it causes both impaired gas exchange and acute right ventricular strain, explaining why it can range from subtle symptoms to sudden cardiovascular collapse and death.

Pneumonia is an acute infection of the lung parenchyma in which inflammation and alveolar exudate impair normal gas exchange. Understanding pneumonia is essential because its physiological effects—alveolar consolidation, ventilation–perfusion mismatch and systemic inflammation—explain hypoxaemia, respiratory distress and the risk of rapid clinical deterioration.

Respiratory failure occurs when the lungs cannot maintain adequate gas exchange and is classified into Type 1 (hypoxaemic) and Type 2 (hypercapnic) based on the primary abnormality. Understanding the distinction is essential because each type reflects a different physiological failure—impaired oxygenation versus impaired ventilation—and guides assessment, monitoring and management decisions.

Pulmonary oedema is a condition in which fluid accumulates in the interstitial and alveolar spaces of the lungs, impairing gas exchange and lung mechanics. Understanding its pathophysiology is essential for distinguishing cardiogenic causes from non-cardiogenic causes and guiding appropriate clinical management.

Pneumothorax is a condition in which air enters the pleural space, abolishing the negative intrapleural pressure required to keep the lung expanded and leading to partial or complete lung collapse. Understanding this mechanism is essential for recognising how pneumothorax impairs ventilation, why symptoms can progress rapidly, and when the condition becomes life-threatening.

Pleural effusion is the accumulation of excess fluid within the pleural space, which mechanically restricts lung expansion and interferes with normal ventilation and gas exchange. Understanding pleural effusion is important because the underlying mechanism causing fluid accumulation determines its clinical significance, guiding diagnosis, investigation, and management.

Cystic fibrosis is an inherited multisystem disorder caused by defective chloride and sodium transport across epithelial surfaces, leading to thick, dehydrated secretions in the airways. Understanding its pathophysiology is important because it explains the persistent airway obstruction, chronic infection and progressive lung damage that drive respiratory failure and long-term outcomes.

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Asthma is a chronic inflammatory airway disease characterised by episodic, reversible airflow obstruction and bronchial hyperresponsiveness. Understanding asthma is important because it explains why symptoms fluctuate, why triggers differ between individuals, and why effective management must target airway inflammation as well as bronchoconstriction.

Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder characterised by persistent, largely irreversible airflow limitation due to structural damage of the airways and alveoli. Understanding COPD is important because it explains progressive breathlessness, impaired gas exchange, and the long-term respiratory and cardiovascular consequences of chronic exposure to noxious stimuli such as cigarette smoke.