What causes a pleural effusion in the lung?

From the Guidelines

A lung can have an effusion due to various causes, including increased fluid production, decreased fluid absorption, or both, as a result of conditions such as heart failure, infections, cancers, pulmonary embolism, liver or kidney disease, autoimmune conditions, and trauma or surgery to the chest area. The underlying mechanism of pleural effusion is complex and involves multiple factors, including increased permeability of the pleural membrane, increased pulmonary capillary pressure, decreased negative intrapleural pressure, decreased oncotic pressure, and obstructed lymphatic flow 1. According to the most recent guidelines, there are over 60 recognized causes of pleural effusions, including disease local to the pleura or underlying lung, systemic conditions, organ dysfunction, and drugs 1.

The pathophysiology of pleural effusions varies according to the underlying aetiologies, and a systematic approach to investigation is necessary to establish a diagnosis swiftly while minimizing unnecessary invasive investigations 1. A careful history and physical examination of the patient remains the most important first step when evaluating someone with an undiagnosed pleural effusion, and thoracic ultrasound (TUS) is now an essential diagnostic tool and should be performed on every patient at their initial presentation and again whenever a pleural procedure is being performed 1.

Key points to consider in the diagnosis and management of pleural effusions include:

• The importance of a thorough history and physical examination to guide further investigations
• The use of thoracic ultrasound as a diagnostic tool and to improve the safety of invasive procedures
• The need to consider a wide range of potential causes, including heart failure, infections, cancers, and autoimmune conditions
• The importance of addressing the underlying cause of the effusion, while sometimes requiring drainage procedures for large or symptomatic effusions
• The use of medications such as diuretics and antibiotics as part of the treatment plan, depending on the underlying cause of the effusion 1.

In terms of imaging, chest radiographs, thoracic ultrasound, and chest CT can all be used to detect pleural effusions, with chest CT being considered the reference standard for imaging 1. The most recent and highest quality study recommends a systematic approach to investigation, including a careful history and physical examination, thoracic ultrasound, and imaging studies as needed, to establish a diagnosis and guide management 1.

From the Research

Causes of Lung Effusion

• A lung can have an effusion due to various underlying diseases, including congestive heart failure, cancer, pneumonia, and pulmonary embolism 2.
• Pleural effusion can result from increased interstitial fluid in the lung due to elevated pulmonary capillary pressure in heart failure (HF) 3.
• Malignant pleural effusions can occur in patients with lung cancer, with around 20% of patients having minimal pleural effusions 4.
• Other causes of pleural effusion include systemic disorders, disorders of the lung or pleura, and conditions such as empyema 5.

Characteristics of Pleural Effusion

• Pleural effusions can be classified as transudates or exudates, with transudative effusions typically managed by treating the underlying medical disorder 5.
• The fluid in pleural effusions can meet the biochemical characteristics of a transudate or an exudate, with some cases falling into the exudative range 3.
• Testing for natriuretic peptides, such as NT-proBNP, can aid in diagnosing or excluding HF in patients with pleural effusion of unknown origin 3.

Diagnosis and Treatment

• Thoracocentesis should be performed for new and unexplained pleural effusions to determine the etiology of the effusion 5.
• Laboratory testing, including chemical and microbiological studies, as well as cytological analysis, can provide further information about the etiology of the disease process 5.
• Treatment of pleural effusion depends on the underlying etiology, with options ranging from pleurodesis to thoracoscopy and video-assisted thoracoscopy 2.
• The presence of a clinically significant pleural effusion is independently associated with higher all-cause mortality in patients with admitting diagnosis of CHF, cancer, and pneumonia 6.