U01.16.042 Pleural effusions

Pleural effusions refer to the excess accumulation of fluid between the pleural layers, which can significantly impact respiratory function. This condition can lead to restricted lung expansion during inspiration and may require medical intervention.

Types of Pleural Effusions

1. Lymphatic Effusions (Chylothorax)

Definition: Accumulation of chylous fluid due to thoracic duct injury, often resulting from trauma or malignancy.
Characteristics:
- The milky appearance of fluid
- High triglyceride content

2. Exudative Effusions

Definition: Fluid with a higher protein content that is typically associated with various pathological conditions.
Characteristics:
- Protein content: > 2.9 g/dL
- Appearance: Cloudy and cellular
Causes:
- Malignancy
- Inflammation/infection (e.g., pneumonia, collagen vascular disease)
- Trauma (increased vascular permeability)
Management: Must be drained to reduce the risk of infection.

3. Transudative Effusions

Definition: Fluid that results from systemic processes affecting the pleural space without significant local disease.
Characteristics:
- Protein content: < 2.5 g/dL
- Appearance: Clear and hypocellular
Causes:
- Decreased hydrostatic pressure (e.g., heart failure, sodium retention)
- Decreased oncotic pressure (e.g., nephrotic syndrome, cirrhosis)

Points to Remember

Diagnosis: The type of pleural effusion can often be determined through thoracentesis and analysis of the fluid.
Thoracentesis: A procedure used to remove or reduce pleural fluid, providing relief from symptoms and facilitating diagnosis.
Infection Risk: Exudative effusions must be monitored closely for potential infection due to their cellular content.

Table: Comparison of Pleural Effusion Types

Type	Protein Content	Appearance	Causes	Management
Lymphatic	Variable	Milky	Thoracic duct injury (trauma/malignancy)	Drainage, manage underlying cause
Exudate	> 2.9 g/dL	Cloudy	Malignancy, inflammation/infection, trauma	Drainage
Transudate	< 2.5 g/dL	Clear	Heart failure, nephrotic syndrome, cirrhosis	Treat underlying condition

Table: Comparison of Pleural Effusion Types

Bibliography

Light, R. W. (2013). Pleural Diseases. Lippincott Williams & Wilkins.
Schreiber, A. (2017). “Diagnosis and Management of Pleural Effusion.” American Family Physician. Retrieved from AAFP.
Bankier, A. A., & Kull, Z. (2018). “Pleural effusion: a review of imaging and management.” Journal of Thoracic Disease, 10(9), 5476-5484. DOI: 10.21037/jtd.2018.08.55.

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USMLE Step 1 Review Series

Curriculum

U01.16.042 Pleural effusions

Types of Pleural Effusions

1. Lymphatic Effusions (Chylothorax)

2. Exudative Effusions

3. Transudative Effusions

Points to Remember

Table: Comparison of Pleural Effusion Types

Bibliography

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