08. Pleural Effusions

Thoracentesis

To help differentiate between exudates and transudates. Indicated for all new pleural effusions >10 mm thick on decubitus view or ultrasonography. If a patient presenting with CHF who is afebrile and without chest pain has bilateral effusions of similar size, a trial of diuresis can be attempted first. Suspected parapneumonic effusions should be tapped immediately. If clinical suspicion for pleural sepsis exists, can consider placing a small caliber chest tube. See Procedures: Thoracentesis.

Imaging

  • PA film: at least 175 ml of fluid must accumulate before effusion is visible.
  • Lateral decubitus film: very sensitive (<10 ml in some studies); helps to differentiate freely flowing vs. loculated fluid.
  • Ultrasonography: used to guide thoracentesis in small or loculated effusions.
  • CT: used to evaluate complex situations (e.g., outline loculated collections).

Studies

  • Pleural fluid: total protein, LDH, cell count with differential, glucose, gram stain with culture (including AFB), and pH. Other studies include cytology (if malignancy suspected), amylase (if pancreatic or esophageal etiology suspected), cholesterol (if chyliform effusion suspected), adenosine deaminase (if tuberculous pleural effusion suspected), and triglycerides (if chylothorax suspected). Note gross fluid appearance (straw-colored, purulent, etc.).
    • Pleural total protein can be falsely elevated in the context of diuresis.
  • Serum: total protein and LDH.
  • pH is a difficult test and needs to be treated in the same way as an ABG (i.e., quickly stored on ice and processed in a blood gas analyzer) or results can be falsely elevated. Discuss with your lab if this is possible before sending. Glucose is often used in conjunction with pH to determine biochemical complexity of the effusion.
  • ADA is elevated in TB, rheumatologic disease, and malignancy; however, ADA >35 U/L has a sensitivity of 86% and specificity of 87% for TB, but only in high-risk populations.
  • Pleural biopsy is considered the gold standard for the evaluation of the unexplained exudative effusion.

Light's Criteria (Exudate vs. Transudate)

  • To be an exudate, an effusion has to meet only one of the following criteria (98% sensitive, 83% specific for exudates):
    • Pleural fluid/serum LDH ratio >0.6.
    • Pleural fluid/serum total protein ratio >0.5.
    • Pleural fluid LDH >2/3 the upper limit of normal.
  • Transudate: CHF (80% bilateral), hepatic hydrothorax, nephrotic syndrome, peritoneal dialysis, myxedema, acute atelectasis, constrictive pericarditis, SVC syndrome, pulmonary embolism (usually exudate), hypoalbuminemia.
  • Exudate: infection (bacterial, parapneumonic, TB, viral, fungal, parasitic), malignancy (primary lung cancer more commonly than metastases), collagen vascular disease, pulmonary embolism, pancreatitis, esophageal rupture, hemothorax, chylothorax, sarcoidosis, drug reaction, post-MI or CABG, Meigs’ syndrome, uremia.

Exudative Effusions

Parameter

Associated Etiology

Glucose <60 mg/dL or ratio fluid/serum <0.5

Complicated parapneumonic effusion vs. empyema, tuberculous pleural effusion, malignant effusion, lupus or rheumatoid pleurisy, esophageal rupture (glucose usually <10 in rheumatoid pleurisy and empyema)

pH <7.2

Empyema or complicated parapneumonic, rheumatoid, esophageal rupture (<6), TB, malignancy, hemothorax, systemic acidosis, parasitic

High amylase

Esophageal rupture, pancreatitis, malignancy

Bloody (RBCs >100k; pleural Hct >50% of peripheral Hct)

Trauma, malignancy, pulmonary embolism or infarction, TB

Neutrophils >50%

Acute inflammation

Lymphocytes >50%

Lymphoma or other malignancy, TB or fungi, post-pericardiotomy or chronic effusion

Eosinophilia >10%

Commonly associated with air or blood in the pleural space, occasionally associated with malignancy

Parapneumonic effusions

  • Uncomplicated: negative gram stain and culture, pH >7.2, glucose >60 mg/dL, no loculations.
  • Complicated: positive gram stain or culture or pH <7.2 or glucose <60 mg/dL. Consider for LDH >1,000 IU/L.
  • Empyema: aspiration of frank pus during thoracentesis, positive smear or culture, cell count with >50k WBCs. Warrants chest tube placement ASAP.

Management

  • Transudative effusions do not require therapeutic drainage unless they are very large and are causing unmanageable dyspnea. Treat the underlying cause.
  • Uncomplicated parapneumonic or tuberculous effusions usually resolve with antibiotics and do not require chest tubes.
  • Complicated parapneumonic effusions and empyema require chest tube placement to prevent formation of pleural "peels" that may trap lung and cause loss of lung function. Loculated effusions may require multiple tubes, administration of tPA, or surgical decortication.
  • Malignant effusions (which usually herald unresectable cancer) that recur after thoracentesis may be managed with serial therapeutic taps, pleurodesis, or an indwelling pleural catheter. The American Thoracic Society recommends a definitive intervention upon first recurrence of a symptomatic malignant effusion.

 

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David J Feller-Kopman et al. Management of Malignant Pleural Effusions. An Official ATS/STS/STR Clinical Practice Guideline. Am J Respir Crit Care Med. 2018 Oct 1;198(7):839-849.