Pleural Effusion

Question 1

Pleural Effusion Definition

Answer 1

• 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

Question 2

Terms

Answer 2

hydrothorax

hemothorax

empyema

chylothorax

Question 3

Most Common Causes of Pleural Effusion

Answer 3

• congestive heart failure
• pneumonia
• malignancy
• pulmonary embolism

Question 4

Mechanisms of Pleural Fluid Formation

Answer 4

• 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)

Question 5

Pleural Effusion Symptoms

Answer 5

– Dyspnea—mostly due to altered mechanics of breathing (distortion of chest wall and diaphragm) rather than hypoxemia

– Chest pain—if inflammation

– Cough

Question 6

Pleural Effusion Physical Findings

Answer 6

(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

Question 7

Exudates

Answer 7

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.

Question 8

More Common Causes of Exudates

Answer 8

• 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

Question 9

Thoracentesis

Answer 9

• 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.

Question 10

Characteristics of Normal Pleural Fluid

Answer 10

– 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

Question 11

Transudate vs exudate

Answer 11

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.

Question 12

Pleural Fluid Analysis

Answer 12

• 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

Question 13

Transudate vs Exudate—Light Criteria

Answer 13

• 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.

Question 14

Alternative Criteria

Answer 14

• 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

Question 15

False Positive Exudate

Answer 15

• 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.

Question 16

Common Lab Tests - Pleural Fluid

Answer 16

• Protein
• LDH
• Cholesterol
• Glucose
• pH
• Cell Count / Differential
• Gram stain / Culture
• Cytology

Question 17

Less Common Lab Tests - Pleural Fluid

Answer 17

• Amylase
• Triglycerides
• Fungal culture
• AFB culture

Question 18

Thoracentesis Contraindications

Answer 18

– 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.

Question 19

Thoracentesis Complications

Answer 19

– 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.

Question 20

Glucose

Answer 20

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.

Question 21

pH

Answer 21

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.

Question 22

Amylase

Answer 22

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

Question 23

Pleural Fluid Cells - Lymphocytes

Answer 23

Pleural fluid lymphocytosis, particularly with lymphocyte counts representing 85 to 95 percent of the total nucleated cells, suggests tuberculous pleurisy or malignancy.

Question 24

Pleural Fluid Cells - Neutrophils

Answer 24

Neutrophil counts above 50,000/microL in pleural fluid are usually found only in complicated parapneumonic effusions, including empyema.

Question 25

Pleural Fluid Cells - Eosinophils

Answer 25

Pleural fluid eosinophilia (defined by pleural fluid eosinophils representing more than 10 percent of the total nucleated cells) is commonly associated with air or blood in the pleural space and is often the result of a previous thoracentesis. Eosinophilia in the pleural fluid may occur with fungal or parasitic infection, drug reaction, or malignancy

Question 26

Tuberculous pleuritis

Answer 26

• Suspect tuberculous pleuritis in patients with a history of exposure or a positive PPD finding and in patients with lymphocytic exudative effusions
• Because most tuberculous pleural effusions probably result from a hypersensitivity reaction to the Mycobacterium rather than from microbial invasion of the pleura, acid-fast bacillus stains of pleural fluid are rarely diagnostic (< 10% of cases), and pleural fluid cultures grow M tuberculosis in less than 65% of cases

Question 27

Why do the majority of malignant pleural effusions occur in women?

Answer 27

The majority of malignant pleural effusions occur in women because malignant pleural effusions are significantly associated with breast and gynecologic malignancies.

Question 28

Diagnosis

Answer 28

•Imaging

• chest X-ray
• CT
• Pleural effusions accumulate in the most dependent part of the thoracic cavity because the lung, which is physically less dense than liquid, floats on the effusion. Because of gravity, the initial accumulation of pleural liquid occurs in a subpulmonic location between the inferior surface of the lower lobes and the diaphragm. Up to 75 mL of pleural effusion can occupy the subpulmonic space without spillover. As it accumulates, pleural liquid spills over into the costophrenic sulcus posteriorly, anteriorly, and laterally. It surrounds the lung and forms a cloak, or cylinder, which looks like a meniscus in radiographic projections.
• On decubitus radiographs, small amounts of fluid can be identified.
• CT detects small pleural effusions but also identifies thickening of the visceral and parietal pleura. Enhancement of the visceral and parietal pleura after injection of intravenous contrast material (the “split pleura sign”) demonstrates the presence of inflammation and thus an exudative, rather than transudative, effusion.

•Thoracentesis/Pleural Fluid Analysis

Question 29

Transudates

Answer 29

• Transudates are usually ultrafiltrates of plasma due to imbalances in hydrostatic and oncotic pressures in the chest, but can also result from movement of fluid from other areas such as the peritoneal cavity in patients with ascites.
• The most common causes of transudative effusions are congestive heart failure, hypoalbuminemia, nephrotic syndrome, or cirrhosis.

Question 30

Hydrothorax

Answer 30

Hydrothorax is a type of pleural effusion in which transudate accumulates in the pleural cavity. This condition is most likely to develop secondary to congestive heart failure, following an increase in hydrostatic pressure within the lungs.

Question 31

Hemothorax

Answer 31

• A hemothorax (derived from hemo- [blood] + thorax [chest], plural hemothoraces) is an accumulation of blood within the pleural cavity. The symptoms of a hemothorax include chest pain and difficulty breathing, while the clinical signs include reduced breath sounds on the affected side and a rapid heart rate.
• The most common cause of hemothorax is chest trauma. Hemothorax can also occur in people who have: Blood clotting defect. Chest (thoracic) or heart surgery.

Question 32

Empyema

Answer 32

Empyema is defined as a collection of pus in the pleural cavity, gram-positive, or culture from the pleural fluid. Empyema is usually associated with pneumonia but may also develop after thoracic surgery or thoracic trauma.

Question 33

Chylothorax

Answer 33

A chylothorax is a type of pleural effusion (a collection of fluid between the membranes lining the lungs called the pleura), but instead of normal pleural fluid, it’s a collection of chyle (lymph fluid). It is caused by a blockage or disruption of the thoracic duct in the chest.