Pleural Effusion Flashcards
Pleural Effusion Definition
- abnormal collection of fluid in the pleural space usually resulting from excess fluid production or decreased absorption
- The normal pleural space contains approximately 10-20 mL of fluid, representing the balance between
(1) hydrostatic and oncotic forces in the visceral and parietal pleural vessels and
(2) extensive lymphatic drainage.
Pleural effusions result from disruption of this balance
Terms
hydrothorax
hemothorax
empyema
chylothorax
Most Common Causes of Pleural Effusion
- congestive heart failure
- pneumonia
- malignancy
- pulmonary embolism
Mechanisms of Pleural Fluid Formation
- Increased capillary hydrostatic pressure in the systemic and/or pulmonary circulation (e.g., CHF)
- Reduction in intravascular oncotic pressure (e.g., hypoalbuminemia, cirrhosis, nephrotic syndrome)
- Increased capillary permeability or vascular disruption (e.g., malignancy, inflammation, infection, pancreatitis)
- Decreased lymphatic drainage or complete blockage, including thoracic duct obstruction or rupture (e.g., malignancy, trauma)
- Increased peritoneal fluid, with migration across the diaphragm via the lymphatics or structural defect (e.g., cirrhosis, peritoneal dialysis)
Pleural Effusion Symptoms
– Dyspnea—mostly due to altered mechanics of breathing (distortion of chest wall and diaphragm) rather than hypoxemia
– Chest pain—if inflammation
– Cough
Pleural Effusion Physical Findings
(if significant effusion, >250ml)
– Decreased expansion
– Dullness to percussion
– Decreased breath sounds and decreased tactile fremitus
– Tracheal shift away from large effusion; if trachea shifted toward effusion, mainstem bronchial obstruction (beware of total lung atelectasis without significant effusion)
– Pleural friction rub
Exudates
Exudates are produced by a variety of inflammatory conditions and often require more extensive evaluation and treatment than transudates.
– Exudates arise from pleural or lung inflammation, impaired lymphatic drainage of the pleural space, and increased capillary wall permeability or vascular disruption. Permeability of pleural capillaries to proteins is high, resulting in an elevated protein content.
More Common Causes of Exudates
• The more common causes of exudates include the following:
– Parapneumonic causes
– Malignancy
– Collagen vascular diseases (rheumatoid arthritis, SLE)
– Pulmonary embolism
– Tuberculosis
– Other
- Pancreatitis
- Trauma
- Postcardiac injury syndrome
- Esophageal perforation
- Sarcoidosis
- Fungal infection
- Drugs
- Chylothorax
Thoracentesis
• Thoracentesis should be performed for new and unexplained pleural effusions when sufficient fluid is present to allow a safe procedure. Observation of pleural effusion is reasonable when benign etiologies are likely, as in the setting of overt congestive heart failure, viral pleurisy, or recent thoracic or abdominal surgery.
Characteristics of Normal Pleural Fluid
– Clear ultrafiltrate of plasma that originates from the parietal pleura
– A pH of 7.60-7.64
– Protein content of less than 2% (2 g/dL)
– Fewer than 1000 white blood cells (WBCs) per cubic millimeter
– Glucose content similar to that of plasma
– Lactate dehydrogenase (LDH) less than 50% of plasma
Transudate vs exudate
In a pleural effusion, different fluids can enter the pleural cavity. Transudate is fluid pushed through the capillary due to high pressure within the capillary. Exudate is fluid that leaks around the cells of the capillaries caused by inflammation.
Pleural Fluid Analysis
• Laboratory testing helps to distinguish pleural fluid transudates from exudates; however, certain types of exudative pleural effusions might be suspected simply by observing the gross characteristics of the fluid obtained during thoracentesis. Note the following:
– Frankly purulent fluid indicates an empyema
– A putrid odor suggests an anaerobic empyema
– A milky, opalescent fluid suggests a chylothorax, resulting most often from lymphatic obstruction by malignancy or thoracic duct injury by trauma or surgical procedure
– Grossly bloody fluid may result from trauma, malignancy, or asbestos-related
Transudate vs Exudate—Light Criteria
- Tests first proposed by Light have become the standards
- The fluid is considered an exudate if any of the following applies:
– Ratio of pleural fluid to serum protein greater than 0.5
– Ratio of pleural fluid to serum LDH greater than 0.6
– Pleural fluid LDH greater than two thirds of the upper limit of normal serum value
• Clinical judgment is required when pleural fluid test results fall near the cutoff points.
Alternative Criteria
• The Light criteria require simultaneous measurement of pleural fluid and serum protein and LDH.
– A meta-analysis of 1448 patients demonstrated that the following combined pleural fluid measurements have sensitivity and specificity comparable to the Light criteria for distinguishing transudates from exudates
– Pleural fluid LDH value greater than 0.45 of the upper limit of normal serum value
– Pleural fluid cholesterol level greater than 45 mg/dL
– Pleural fluid protein level greater than 2.9 g/dL
False Positive Exudate
- The Light criteria (or the alternative criteria) identify nearly all exudates correctly, but they misclassify approximately 20-25% of transudates as exudates, usually in patients on long-term diuretic therapy for congestive heart failure (because of the increased concentration of protein and LDH within the pleural space due to diuresis).
- Although pleural fluid albumin is not typically measured, a gradient of serum albumin to pleural fluid albumin of less than 1.2 g/dL also identifies an exudate in such patients.
Common Lab Tests - Pleural Fluid
- Protein
- LDH
- Cholesterol
- Glucose
- pH
- Cell Count / Differential
- Gram stain / Culture
- Cytology
Less Common Lab Tests - Pleural Fluid
- Amylase
- Triglycerides
- Fungal culture
- AFB culture
Thoracentesis Contraindications
– Relative contraindications to diagnostic thoracentesis include a small volume of fluid (< 1 cm thickness on a lateral decubitus film), bleeding diathesis or systemic anticoagulation, mechanical ventilation, and cutaneous disease over the proposed puncture site.
Thoracentesis Complications
– Complications of diagnostic thoracentesis include pain at the puncture site, cutaneous or internal bleeding, pneumothorax, and spleen/liver puncture. Pneumothorax is a complication of thoracentesis but requires treatment with a chest tube in less than 5% of cases.
Glucose
A low pleural fluid glucose concentration (less than 60 mg/dL) or a pleural fluid/serum glucose ratio less than 0.5 narrows the major differential diagnoses to rheumatoid or lupus pleurisy, tuberculous pleurisy or other infection, malignant effusion, and esophageal rupture. The lowest glucose concentrations are found in rheumatoid pleurisy and empyema, with glucose being undetectable in some cases.
pH
A pleural fluid pH below 7.30 with a normal arterial blood pH is found with the same diagnoses associated with low pleural fluid glucose concentrations. The pH of normal pleural fluid is approximately 7.60, due to a bicarbonate gradient between pleural fluid and blood. A parapneumonic effusion with a low pleural fluid pH (≤7.15) indicates a high likelihood of necessity for pleural space drainage.
Amylase
Measurement of amylase in pleural fluid can assist in settings in which pancreatic or esophageal etiologies of an effusion appear possible. The finding of an amylase-rich pleural effusion, defined as either a pleural fluid amylase greater than the upper limits of normal for serum amylase or a pleural fluid to serum amylase ratio greater than 1.0, narrows the differential diagnosis of an exudative effusion to pancreatitis, esophageal rupture, or malignancy. In acute pancreatitis and esophageal rupture, amylase levels are usually extremely high
Pleural Fluid Cells - Lymphocytes
Pleural fluid lymphocytosis, particularly with lymphocyte counts representing 85 to 95 percent of the total nucleated cells, suggests tuberculous pleurisy or malignancy.
Pleural Fluid Cells - Neutrophils
Neutrophil counts above 50,000/microL in pleural fluid are usually found only in complicated parapneumonic effusions, including empyema.
