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Pleural Effusions

David Krasinski, Eddie Qian


  • There is a normal influx of fluid into the pleural space due to leaky capillary membranes and the pleural space’s negative pressure. This fluid is constantly reabsorbed by lymphatics. An imbalance in the system will result in accumulation.

  • Examples of dysfunction in homeostasis:

    • Increased influx: ↑ filtration from the capillaries from high intravascular hydrostatic pressure (e.g. heart failure, renal failure) or low intravascular oncotic pressure
    • Other liquid entry into the pleural space through anatomic deficits: CSF, chyle, urine, blood, ascites (the diaphragm is naturally porous)
    • Decreased efflux: obstruction of the parietal pleural stoma (from protein or cellular debris in exudative pleural effusions)
    • Increased systemic venous pressure: lymphatic system drains into the systemic venous circulation so high venous pressure prevents lymphatics from draining appropriately


  • May be asymptomatic

  • Chest pain: usually pleuritic via parietal pleural innervation

  • Dyspnea and tachypnea without hypoxia (unless concurrent airspace disease): Dyspnea isthought to be mediated by branches of the phrenic n. that are under pressure from effusion

  • Exam: ↓ breath sounds, ↓ chest wall excursion, ↓ tactile fremitus, dullness to percussion


  • CXR: Ideally supine AP, lateral upright and decubitus lateral. Fluid accumulates first in subpulmonic space and then in posterior costophrenic recess

  • 50cc: Visible in posterior costophrenic angle on lateral film

  • 200cc: Visible on AP costophrenic angle on AP film

  • 500cc: Obliteration of hemidiaphragm

  • If effusion moves with gravity, suggests free flowing

  • POCUS: assess size, location, loculations

  • CT with contrast: not always indicated; helpful to evaluate septations

  • Thoracentesis: see “Procedures section”

Interpretation of pleural studies

  • Obtain pleural LDH, protein, cell count/diff, gram stain w/ culture, pH. Consider pleural cytology, hematocrit, triglyceride, glucose, and amylase. Need serum LDH and protein.

  • Lights criteria: 1 of the following to be considered an exudative effusion

    • Pleural to serum protein ratio > 0.5
    • Pleural to serum LDH ratio > 0.6
    • Pleural LDH > ⅔ upper limit of normal range of serum LDH
  • Transudative: CHF exacerbation, hepatic hydrothorax, atelectasis (caused by increased intrapleural negative pressure), hypoalbuminemia, renal failure

  • Exudative: infections (bacterial, TB, fungal), malignant, rheumatologic, PE

  • Hemothorax: pleural hematocrit >50% of blood hematocrit

  • Chylothorax: pleural TG >100mg/dl

  • Concern for esophageal rupture: elevated salivary amylase

  • Other tips:

    • Protein: >5 think TB or malignancy, < 0.5 think urine, CSF, peritoneal dialysate
    • Glucose: < 60 think about malignancy, TB, or rheumatologic, less likely hemothorax or parapneumonic
    • Cell count/diff: polys represent an acute process, monocytes represent a chronic process, lymphocytes think about TB or malignancy, eosinophils think about air/blood, TB, malignancy, asbestos, drugs
    • Two separate processes may co-occur, and a transudate may mask an exudative effusion; if concerned for this and you have clinical stability, trial diuresis prior to thoracentesis


  • Parapneumonic effusion: most common exudative process

    • Uncomplicated: systemic antibiotic for pneumonia
    • Complicated (positive culture or gram stain, OR loculated OR pH<7.20 OR glucose less than 60): needs chest tube + MIST2 protocol (intrapleural alteplase 10 mg BID in 30 mL of saline AND intrapleural DNase 5 mg BID in 30 mL of water for a total of 3 days)
  • Hepatic hydrothorax: Avoid chest tubes. Cirrhosis medical management ± TIPS. Spontaneous bacterial empyema might occur. Perform thoracentesis if suspected.

  • Tuberculosis effusions: Treat as active TB. Often resolves with treatment.

  • Malignant pleural effusion: If cytology isolates malignant cells in pleural space, this often automatically classifies that malignancy as an advanced/metastatic stage. Tends to recur.

    • If recurrent, either do 1) serial thoracentesis, 2) PleurX catheter (tunneled chest tube) or 3) chemical pleurodesis (obliteration of pleural space with talc or tetracycline)