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Pleural Effusion 

Pleural Effusion
Pleural Effusion

Michael P. Mendez

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date: 05 July 2022

  1. A. Introduction

    1. a. Because pleural effusions occur with many medical conditions, health care providers need a systematic and straightforward approach to diagnosis and management.

    2. b. Pleural fluid can consist of anything—from simple serous liquid to complicated pleural infections and hemorrhage.

    3. c. The three most common causes of pleural effusion in the United States are congestive heart failure, pneumonia, and malignancy.

  2. B. Causes of Pleural Effusion

    1. a. As there are many causes of pleural effusion, the most clinically useful approach is to categorize the effusion as transudative or exudative (Table 24.1).

      Table 24.1 Common Causes of Pleural Effusions



      Congestive heart failure

      Infections (tuberculosis, fungal disease, viral or bacterial pneumonia)

      Hepatic hydrothorax

      Collagen vascular disease (lupus, rheumatoid arthritis)

      Nephrotic syndrome

      Neoplasm (mesothelioma, lymphoma, metastases)


      Gastrointestinal disease (pancreatitis, esophageal rupture, subdiaphragmatic abscess)



      Pulmonary embolism

      Pulmonary embolism

      Miscellaneous (chylothorax, following cardiac surgery, asbestos related)

      1. i. Transudative effusions are fluid collections that are caused by an alteration in Starling forces (i.e., elevated hydrostatic pressure, decreased oncotic pressure). These usually resolve with treatment of the underlying disorder (e.g., heart failure, cirrhosis).

      2. ii. Exudative effusions are more concerning because they reflect primary pleural disease. They often require removal (either by thoracentesis or tube thoracostomy) to prevent scarring and infection from developing.

  3. C. Clinical Manifestations of Pleural Effusion

    1. a. History

      1. i. Patients with pleural effusions typically present with dyspnea and pleuritic chest pain. However, in some cases pleural effusions may be completely asymptomatic.

      2. ii. Symptoms may be indolent or rapidly progressive depending on the rate of fluid accumulation.

      3. iii. Fevers, chills, and night sweats can occur if effusions are infected.

    2. b. Physical examination

      1. i. The physical examination generally reveals dullness to percussion, absent or diminished breath sounds, and decreased tactile fremitus.

      2. ii. A horizontal band of egophony can often be elicited just above the area of dullness. Egophony results from compressive atelectasis of the overlying lung by the effusion.

  4. D. Approach to the Patient

    1. a. Chest imaging. The chest radiograph is the first test to order when evaluating a patient with suspected pleural effusion. Effusions of more than 200 mL should be visible on the posterior-anterior view. Smaller effusions (50–200 mL) may be visible on a lateral radiograph only. Ultrasound can be used to more reliably detect small effusions.

      1. i. Small effusions cause blunting of the costophrenic angle.

      2. ii. Larger effusions opacify the lower lung fields.

      3. iii. At times, it is difficult to distinguish a pleural effusion from a consolidative process in the lung. A lateral decubitus radiograph can help distinguish between the two by demonstrating dependent layering of pleural fluid. If available, a portable ultrasound machine allows for rapid identification and/or confirmation of suspected effusion.

      4. iv. Occasionally, pleural effusions do not layer, and additional imaging (ultrasound or chest computed tomography [CT]) is required.

    2. b. Diagnostic thoracentesis

      1. i. When to perform a diagnostic thoracentesis. After a pleural effusion is identified, diagnostic thoracentesis should always be considered, especially if the cause is unknown. However, if a patient has a likely cause (e.g., history of congestive heart failure) and presents with classic findings (e.g., bilateral effusions of relatively equal size without evidence of infection), it is reasonable to attempt diuresis and perform diagnostic thoracentesis if the effusions persist beyond 48 hours.

      2. ii. Distinguishing between transudative and exudative. Pleural fluid should be sent to the laboratory to determine whether it is transudative or exudative. Additionally, exudative complicated or uncomplicated effusions can be elucidated (Table 24.2). If certain specific etiologies are suspected, additional studies should be performed (Table 24.3).

        Table 24.2 Interpretation of Pleural Fluid Analysis




        Clinical Tips

        Lactate dehydrogenase (LDH)

        Exudative if pleural value >60% serum or more than two-thirds the upper limit of normal of serum value

        Draw serum at the time of thoracentesis

        Total protein

        Exudative if pleural value >50% serum value


        Normal or low (<60 mg/dL)


        Very low in empyema or rheumatoid arthritis


        Normal or low (<7.20)


        Draw in heparinized syringe. Keep on ice!

        Cell count

        >10,000/mm3 white blood cells

        <10,000/mm3 white blood cells

        >100,000/mm3 red blood cells suggests trauma, malignancy, or pulmonary embolism


        Neutrophil predominance

        Macrophage predominance with presence of mesothelial cells

        Lymphocytic predominance (50%–80%) suggests malignancy or tuberculosis

        Gram stain and culture

        No organisms unless empyema

        No organisms

        Table 24.3 Additional Pleural Fluid Studies Often Required and Associated Conditions


        Associated Conditions


        Pancreatitis, esophageal rupture, malignancy





        Acid-fast stain and culture

        Mycobacterial disease



        Adenosine deaminase


        1. 1. Comparison of pleural and serum levels of total protein and lactate dehydrogenase (LDH) allow for distinction between transudative and exudative effusions (see Table 24.2)

        2. 2. The pleural fluid is considered exudative if any of the following three criteria (i.e., Light’s criteria) are met:

          • a. Fluid LDH–to–serum LDH ratio >0.6.

          • b. Fluid LDH is more than two-thirds the upper limit of normal of serum LDH.

          • c. Fluid protein–to–serum protein ratio >0.5.

        3. 3. Pleural fluid glucose, pH, and Gram stain with culture should be performed on all pleural fluid to determine whether the effusion is complicated and/or infected (see Table 24.2). A complicated effusion has an unacceptably high likelihood of scarring and lung damage. An effusion is considered complicated if one of the following criteria is present:

          • a. Fluid pH <7.20.

          • b. Fluid glucose <60 mg/dL.

          • c. Gram stain or culture from fluid is positive for organisms.

            Hot Key

            An empyema, a type of complicated effusion, is defined by the presence of organisms in the pleural fluid on gram stain or culture

        4. 4. A cell count with differential should be performed to help determine the etiology of an exudative effusion.

        5. 5. Pleural fluid levels of amylase, triglycerides, and creatinine; acid-fast staining and culture; and cytology should be ordered when specific diagnoses are entertained (see Table 24.3).

        6. 6. Occasionally, some (about 25%) transudative effusions are misclassified as exudative by Light’s criteria. If a transudative effusion is clinically suspected, more specific tests can confirm or refute the result. In particular, a serum albumin level 1.2 g/dL higher than the pleural fluid albumin level suggests a transudative effusion. Similarly, an effusion cholesterol >45 mg/dL, coupled with an effusion LDH >200 U/L, can help confirm an exudative effusion.

  5. E. Treatment. Treatment is based on etiology and whether there is evidence that the effusion is complicated and/or infected.

    1. a. Transudative effusions rarely require drainage unless they are causing significant discomfort or hypoxemia. Treatment of transudative effusions should generally be directed at the underlying cause.

    2. b. Complicated effusions—especially empyema—should be surgically drained, either by tube thoracostomy or with a thoracoscope. The diagnosis of empyema is made by positive Gram stain or visibly purulent fluid. Empyema also requires antibiotics directed at the causative organism.

    3. c. Some effusions that are not obviously complicated may still require surgical drainage if they appear loculated (the fluid is trapped into multiple noncommunicating pockets), an effusion LDH is greater than three times the upper limit of normal, or the effusion takes up one-half of the hemithorax on chest radiograph.

Table 24.4 Indications for Surgical Evaluation (Chest Tube or Thoracoscopy)

1. Frank pus on thoracentesis

2. Positive Gram stain or culture

3. pH <7.20

4. Glucose <60 mg/dL

5. Lactate dehydrogenase more than three times the upper limit of normal

6. Evidence of loculation on chest imaging

7. Effusion occupies more than one-half of hemithorax (hepatic hydrothorax excluded)

Suggested Further Readings

Corcoran JP, Wrightson JM, Belcher E, DeCamp MM, Feller-Kopman D, Rahman NM. Pleural infection: past, present, and future directions. Lancet Respir Med 2015;3:563–77.Find this resource:

Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med 1972;77:507–13. (Classic Article.)Find this resource:

Wilcox ME, Chong CA, Stanbrook MB, Tricco AC, Wong C, Straus SE. Does this patient have an exudative pleural effusion? The Rational Clinical Examination systematic review. JAMA 2014;311:2422–31.Find this resource: