Wet, Wacky Lungs: A Quick Look At Pleural Effusions

Author: Andrew Cunningham, MD (EM Resident Physician, PGY-1, NUEM) // Edited by: Elizabeth Byrne, MD (EM Resident Physician, PGY-3, NUEM) // Expert Reviewer: Luke Rosiere, MD

Citation: [Peer-Reviewed, Web Publication] Cunningham A, Byrne E (2016, April 26). Wet, Wacky Lungs: A Quick Look At Pleural Effusions. [NUEM Blog. Expert Commentary by Rosiere L]. Retrieved from http://www.nuemblog.com/blog/pleural-effusions-101

The Case

About halfway through a busy shift, you glance up from your computer to see an elderly gentleman with a history of cirrhosis rolling in. He is complaining of worsening shortness of breath and reports he “had this before… and the last time they had to take a bunch of fluid out of my chest.” On auscultation, you hear drastically reduced breath sounds on the right side. The portable chest X-ray is completed and you see the image seen to the right. 

  • What caused this, and what needs to be done about it?
  • What kind of information do you need to help guide your decision-making?
  • Should this patient be getting antibiotics?
  • Or should they be getting a slug of lasix?  

According to the National Cancer Institute, there are 100,000 pleural effusions diagnosed every year, so get ready to see this in your shop!

Etiologies of Pleural Effusions

  • Generally, pleural fall into two categories: exudate or transudate. A pleural effusion can be considered exudative if any of the following conditions of Light’s criteria are met:
    • Pleural fluid protein to serum protein ratio  > 0.5
    • Pleural fluid lactate dehydrogenase (LDH)/serum LDH ratio > 0.6
    • Pleural fluid LDH > 2/3 the upper limit of normal for serum LDH [1]
  • The most common cause of transudative pleural effusions is heart failure, and the most common cause of exudative pleural effusions is pneumonia. That being said, there are more than fifty causes of pleural effusions, so keep a broad differential![2] Here are several of the more common ones, grouped according to exudative versus transudative: [1,3]


Chest X-ray

  • X-ray is the simplest and most available method for evaluating a pleural effusion, and should be performed in all patients.

  • At least 250 to 500 mL of fluid must be present to visualize the effusion on a chest x-ray. The earliest sign that is typically seen on an upright film is blunting of the costophrenic angle. [2,3]

  • When the entire hemithorax is opacified (such as in the film above), it is crucial to look for mediastinal shift on the film. If there is a mediastinal shift, this patient needs an immediate tap! If the mediastinum is shifted toward the effusion, it is important to consider underlying obstruction or disease of the bronchi as well as the lung parenchyma. [3]



Image borrowed from Reference 4, depicting a right sided empyema.

  • CT scans are more sensitive in detecting small effusions and determining the characteristics of loculations. [3] 
  • In addition to giving a thorough evaluation of the pleural space, CT is also able to evaluate the lung parenchyma, hilum, and mediastinum, and reveal underlying disease. [4]
  • Typically, CT scans are only needed in order to obtain more diagnostic information or for planning more complex procedures, such as pleural biopsies. [4] CT scans also have their inherent downsides, such as a lack of portability and increased radiation exposure. As such, these can typically be deferred to an inpatient or outpatient setting, and don’t necessarily need to be done in the ED.



Image borrowed from Reference 4, depicting a pleural effusion on ultrasound. 

  • Ultrasound has surpassed chest X-ray in its ability to detect effusions, estimate volume, and determine characteristics about the fluid. Furthermore, it is able to directly aid in intervention. [4]
  • By placing the probe just above the diaphragm posteriorly and laterally, ultrasound is capable of detecting as little as 5 mL of fluid in the pleural space, and is also capable of detecting loculations. [3,5]
  • Ultrasound is also able to visualize clots in the pleural space, which will appear as internal echoes within the anechoic space of fluid. [5]


  • MRI may have a role in differentiating between the types of fluid in the pleural space, but has limited ability in distinguishing the cause of exudative effusions. [4]



  • The #1 reason to do it in the ED: an unstable patient (tachycardic, tachpneic, hypotensive) whose X-ray reveals a massive fluid collection that’s causing mediastinal shift. These kind of effusions follow the same physiology as tension pneumothorax, so empty ‘em out! [6]
  • New effusions that are larger than 10mm on any type of imaging (XR, ultrasound, CT) should undergo diagnostic thoracentesis. [3]
  • Unless there is the presence of an immediately life-threatening condition such as empyema, hemothorax, or tension hydrothorax causing cardiovascular collapse, drainage can be deferred to an inpatient or outpatient setting. [1] 


  • There are no absolute contraindications to thoracentesis, not even coagulopathy. [3] 
  • If a patient has a new effusion with a clinically obvious diagnosis (heart failure, pneumonia, etc), there is no need to perform a diagnostic thoracentesis. [3] 

How much do I take off?

More is better, right? Wouldn’t draining more from your patient’s pleural effusion make them less symptomatic? Spare them from a repeat procedure? Get them home sooner? Classically, we are taught to take off no more than 1 liter of fluid, as this can lead to the dreaded phenomenon of re-expansion pulmonary edema (RPE). RPE is a rare complication occurring in less than 1% of thoracenteses but the mortality can reach up to 20%. The pathophysiology is not completely understood but a main hypothesis is that after lung re-expansion an acute inflammatory response occurs and subsequently damages the alveolar-capillary membrane.

During a thoracentesis, a majority of patients develop a cough. Coughing is a physiologic sign of lung re-expansion and should not concern you if it were to happen during the procedure. Pleuritic chest pain can also occur as it is secondary to irritation from the catheter. If your patient complains of a vague chest discomfort, this may be an indication to stop your thoracentesis prematurely. Chest discomfort can be an indication of low pleural pressures which indicate little benefit for any further significant fluid removal. Currently there is no evidence that removal of a larger volume necessarily causes re-expansion pulmonary edema but a weak correlation does exists. If RPE does occur, treatment includes supportive measures including diuresis, supplemental oxygen and possibly noninvasive ventilation. [7] 

  • Risk Factors for Developing RPE
    • Young age
    • Long duration of lung collapse
    • Rapid reexpansion
  • Signs and Symptoms of RPE
    • Chest discomfort
    • Frothy sputum
    • Tachycardia
    • Tachypnea
    • Hypoxemia
    • Crackles on lung exam
    • Hemodynamic instability

Take Home Points

  • There are many, many different causes of pleural effusion, with the most common being congestive heart failure. A diagnostic thoracentesis in conjunction with the application of Light’s criteria can help narrow the diagnosis.
  • An X-ray is simple and a mainstay in diagnosis of any patient with suspected pleural effusion. Ultrasound is rising as a more sensitive means of diagnosing effusion, and is also helpful in aiding drainage of effusion. CT has value in determining more complex underlying characteristics of an effusion, but is typically not essential to perform in the ED.
  • If a patient comes in unstable and an X-ray showing a large pleural effusion causing mediastinal shift, drain it immediately! Any patient with a new effusion and an unclear etiology based on history should undergo a diagnostic thoracentesis at some point during their stay. There are no contraindications to performing a thoracentesis, and there is no fluid removal limit (just watch your patient’s pain level and symptomatology).
  • Stop your thoracentesis if your patient complains of chest discomfort (that is not pleuritic) as this is a sign of lower pleural pressures and you are unlikely to drain much more fluid.

Expert Commentary

Thanks Andrew, you provided a fantastic summary of pleural effusions.  While we see these every day, rare is the new or hemodynamically significant pleural effusion.  There are a few things I can add:

  1. Light's Criteria
    • Highly sensitive at the expense of specificity.  Our goal is to identify all exudates.  In doing so, make sure you send both LDH and protein so you don't miss an exudate.  You may, as a result, end up mis-diagnosing a transudate from CHF as an exudate.  Fortunately, there is little danger in doing that and collateral clinical information will help the team upstairs get it right
    • Some pathologies don't fit neatly into transudate or exudate.  Examples include PE, malignancy, sarcoid, amyloid.
  2. Simple transudative effusions can become exudative
    • Don't become complacent just because your CHF patient has always had an effusion.  If effusions become largely asymmetric, there is pleurisy, a fever or no clinical signs of decompensated CHF, consider exudative processes and a thoracentesis
  3. Safe effusions to tap
    • I like the criteria provided by O. Ma in the "Emergency Ultrasound" text:  1.5 cm from parietal to visceral pleura and covering 3 interspaces.  Maximizes diagnostic yield and minimizes pneumothorax
  4. If you use ultrasound, bleeding complications are rare
    • Much like considering contraindications to paracentesis, if you use an ultrasound to locate your effusion, you are very unlikely to cause bleeding even in the setting of anticoagulation, thrombocytopenia or uremia.

Luke Rosiere, MD
Northwestern University Emergency Medicine Class of 2012; Attending Physician at Northwestern Medicine Central DuPage Hospital


    1. Kosowsky, J. M., & Kimberly, H. H. (2014). Pleural Disease. In J. A. Marx, R. S. Hockberger, & R. M. Walls (Eds.), Rosen's Emergency Medicine: Concepts and Clinical Practice. Philadelphia: Elsevier/Saunders.
    2. Bhatnagar, R., & Maskell, N. (2015). The modern diagnosis and management of pleural effusions. BMJ.
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    8. Dewitz A.  (2008).  Additional Ultrasound-Guided Procedures In O.J. Ma (Ed.), Emergency Ultrasound (pp. 546-550).  New York, NY:  McGraw Hill.
    Posted on April 26, 2016 and filed under Pulmonary.