- Clinical science
Pleural effusion is an accumulation of fluid in the pleural cavity between the lining of the lungs and the thoracic cavity (i.e., the visceral and parietal pleurae). The pleural fluid is called a transudate if it permeates (transudes) into the pleural cavity through the walls of essentially intact pulmonary vessels. It is called an exudate if it escapes (exudes) into the pleural cavity through lesions in blood and lymph vessels, e.g., as caused by inflammation and tumors. The accumulation of transudate is typically due to increased hydrostatic pressure (e.g., as in congestive heart failure) and/or decreased oncotic pressure (e.g., as in cirrhosis or nephrotic syndrome). Since transudate is a filtrate, it is typically a clear fluid with low protein and cell content. By contrast, the lesions responsible for the outflow of exudate allow larger molecules and even solid matter to pass into the pleural cavity. For this reason, exudate is a cloudy fluid with a high protein and cell content. The effusion follows gravity and, unless the patient is bedridden, collects in the lower margins of the pleural cavity. Over the area of effusion, percussion generates a dull tone, and breath sounds are diminished or completely absent on auscultation. Ultrasound is the method of choice for confirming the diagnosis. To establish etiology in cases of first-time or idiopathic pleural effusion, a biopsy for microbiological, cytological, and clinical chemistry testing is recommended. Only large pleural effusions lead to shortness of breath and can be drained via a pleural tap (thoracentesis) if necessary. As a general rule, treatment should focus on the underlying condition.
|Common causes|| |
- Patients with a small pleural effusion may be asymptomatic.
- > 300 mL is required for pleural effusion to become evident in the form of:
- Definition: accumulation of pus in the pleural cavity
- Etiology: most commonly occurs secondary to an infected parapneumonic pleural effusion; . Less common causes include untreated hemothorax that becomes infected, ruptured lung abscess, esophageal tear, or thoracic trauma (e.g., thoracic surgery)
- Clinical features
- Chest x-ray
- Chest CT: very good at differentiating empyema from pleural effusion
Thoracocentesis: pleural fluid analysis
- Low glucose (< 60 mg/dL) and pH < 7.2
- See also distinguishing features of .
- Chest tube (thoracostomy) to remove empyema fluid
- Thoracoscopic debridement (removal of pus and pleural fibrosis) if empyema does not resolve after chest tube drainage
- Appropriate systemic antibiotic treatment (based on culture and sensitivity testing)
- Definition: lymphatic fluid from the thoracic duct () accumulates in the pleural cavity.
- Diagnosis: Thoracocentesis with pleural fluid analysis
- Pathophysiology: increased permeation of plasma protein, blood cells, and tumor cells into the pleural space caused by a cancer-related barrier dysfunction of the capillary walls
- Diagnosis: Thoracocentesis with pleural fluid analysis
- Inspection and palpation:
- Asymmetric expansion and unilateral lagging on the affected side
- Reduced due to fluid in the pleural space
- Weak or no breath sounds
- Pleural friction rub
- Percussion: dullness over the area of effusion
- Very small PE (< 300 mL) may not be visible on a chest x-ray, but can be detected on ultrasound.
- Findings: often bilateral and symmetric
- Lateral decubitus view: demonstrates whether fluid is encapsulated (loculated) or free
- Very sensitive and can detect amounts as low as 20 mL
- Hypoechoic/anechoic structures appear in the lower margins of the pleural cavity (costodiaphragmatic recess).
- Even more sensitive than ultrasound
- Aim: removal of fluid from the pleural space for diagnostic (e.g., transudate vs. exudate) and/or therapeutic purposes; should be preceded by imaging
- Any new unilateral effusion > 1 cm on x-ray in an undiagnosed patient
- History of malignant tumor with effusion > 1 cm on x-ray
- Large effusion with dyspnea and/or cardiac decompensation
- Pneumonia with parapneumonic effusion > 5 cm on x-ray
- Heart failure in conjunction with atypical findings (e.g., pleuritic chest pain, fever, unilateral effusion)
- Suspected transudative bilateral effusions with atypical features (e.g., fever, pleuritic chest pain, effusions of disparate size)
- Ultrasound-assisted (if possible) dorsal puncture with the patient sitting upright
- Puncture site: 1–2 ICS beneath the upper margin of the largest pocket of fluid, but not below the 8th ICS
- No more than 1.5 L should be drained with each puncture, as otherwise a may occur.
- One cannula for microbiological analysis → bacterial cultures, Gram, or Ziehl-Neelsen staining (optional)
- One cannula for clinical chemical analysis → total protein content, LDH
- One cannula for pathological analysis → cytological smear to rule out malignant effusion (see "Pathology" below)
|Physical appearance||Does not froth or form clots||Straw-colored fluid (may rarely be hemorrhagic), which froths on shaking and forms clots on standing still|
|Specific gravity||≤ 1.016||> 1.016|
|Glucose||≥ 60 mg/dL|
|Cholesterol||< 60 mg/dL|| |
≥ 60 mg/dL
|Total protein||≤ 30 g/L||> 30 g/L|
|Light's criteria||Pleural fluid protein: serum protein ratio||≤ 0.5||> 0.5|
|Pleural fluid LDH: serum LDH ratio||≤ 0.6||> 0.6|
|Pleural fluid LDH (lactate dehydrogenase)||< ⅔ the upper limit of normal serum LDH||Pleural fluid LDH > ⅔ the upper limit of normal serum LDH|
Pleural fluid with a bloody appearance suggests a malignant etiology!
- Causal: treat underlying condition: e.g., loop diuretics for acute or antibiotics for
- Tube thoracostomy: in recurrent pleural effusion or for urgent drainage of infected and/or loculated effusions
- Video-assisted thoracoscopic surgery (VATS) : indicated for the collection of histological samples in malignant effusions, for parapneumonic effusions that cannot be sufficiently controlled by way of drainage, and for pleural empyema
- Patients with recurrent chylothorax or recurrent malignant effusions may require pleuroperitoneal shunts.
A chest x-ray should be performed after each of these procedures in order to rule out a pneumothorax!