Pulmonary Oedema

Pulmonary oedema, also known as pulmonary congestion, is the excessive accumulation of fluid in the tissue or air spaces (usually alveoli) of the lungs, leading to impaired gas exchange.

This condition can progress to hypoxaemia and respiratory failure. Pulmonary oedema has multiple causes, traditionally classified as cardiogenic (heart-related) or noncardiogenic (other causes).

Pathophysiology

Fluid movement within the lungs is governed by several forces visualised using the Starling equation, which includes hydrostatic and oncotic (protein) pressures. An imbalance in these forces can cause fluid accumulation in the alveoli. The pulmonary wedge pressure, obtainable via pulmonary artery catheterisation, is a key hydrostatic pressure. However, due to complications associated with catheterisation, other imaging modalities and diagnostic methods are preferred.

Classification

Pulmonary oedema is broadly classified into cardiogenic and noncardiogenic types.

Cardiogenic

Cardiogenic pulmonary oedema results from increased hydrostatic pressure, typically due to volume overload or impaired left ventricular function. This raises pulmonary pressure, leading to fluid accumulation in the alveoli. Common causes include:

• Acute exacerbation of congestive heart failure
• Pericardial tamponade
• Heart valve dysfunction, such as mitral valve regurgitation
• Hypertensive crisis

Flash Pulmonary Oedema

Flash pulmonary oedema (FPE) is a severe, acute form of cardiogenic pulmonary oedema. It manifests suddenly with rapid progression, often without chest pain, making it difficult to diagnose as a cardiovascular disease. Treatment focuses on reducing systemic vascular resistance, supplemental oxygenation, and decreasing left ventricular filling pressure.

Noncardiogenic

Noncardiogenic pulmonary oedema is caused by increased microvascular permeability leading to fluid transfer into the alveolar spaces. Causes include:

• Direct lung injury (e.g., inhalation of toxic gases, pulmonary contusion, aspiration)
• Indirect lung injury (e.g., neurogenic causes, sepsis, pancreatitis)
• Special causes (e.g., high altitude pulmonary oedema, hantavirus pulmonary syndrome)

Signs and Symptoms

The most common symptom is dyspnea, accompanied by tachypnea, tachycardia, and cyanosis. Other symptoms include:

• Coughing up blood (pink or red, frothy sputum)
• Excessive sweating
• Anxiety
• Pale skin
• End-inspiratory crackles on auscultation
• Presence of a third heart sound

Diagnosis

Diagnosis involves multiple tests as no single test confirms pulmonary oedema.

Lab Tests

Lab tests assess oxygen saturation, arterial blood gas, electrolytes, renal function, liver enzymes, inflammatory markers, and complete blood count. Elevated BNP levels suggest a cardiac cause, while low BNP levels (<100 pg/ml) suggest noncardiogenic pulmonary oedema.

Imaging Tests

Chest X-rays are widely used and show fluid in alveolar walls, Kerley B lines, increased vascular shadowing, and pleural effusions. Lung ultrasounds are also useful for diagnosing and quantifying lung water. Urgent echocardiography may demonstrate impaired left ventricular function and high pulmonary pressures.

Prevention

Effective control of underlying heart or lung disease can prevent pulmonary oedema. Dexamethasone and sildenafil are used to prevent high altitude pulmonary oedema.

Management

Management focuses on supporting essential functions and treating the underlying cause. Hypoxia may require supplemental oxygen or mechanical ventilation. For cardiogenic pulmonary oedema, diuretics, vasodilators, and CPAP/BiPAP may be used. In cases of cardiogenic shock, inotropic agents or intra-aortic balloon pump may be necessary.

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Self-assessment MCQs (single best answer)

What is the primary symptom of pulmonary oedema?

Which of the following is a common cause of cardiogenic pulmonary oedema?

Flash pulmonary oedema is characterised by:

Which imaging test is widely used to diagnose pulmonary oedema?

Elevated BNP levels in blood tests suggest:

Which of the following is NOT a cause of noncardiogenic pulmonary oedema?

What is the main goal in the management of pulmonary oedema?

A patient with hypoxia due to pulmonary oedema may require:

Which medication is used to prevent high altitude pulmonary oedema?

What is a common symptom of pulmonary oedema that involves the airways?