Intern Review – Parapneumonic Effusions

Written by Patrick Sylvester, OSU EM/IM Resident // Edited by Michael Barrie OSU EM Assistant Professor

“Never let the sun set on a…”

During a recent scanning shift performing point of care ultrasounds, we came across an old adage that we had to google to confirm was true: “Never let the sun set on a…”  We each inserted our own ending based on the wise words we had heard in medical school.  I suppose from the title of this post, you can guess what we ended up talking about—after some googling, that is.  While our argument was settled that one was not to let the sun set on a parapneumonic effusion, we were unsure best practice in more ambiguous cases.

Consider this: you’re called to the bedside of a 60 year-old patient who presented with hypotension, subjective fever, and in Afib w/ RVR.  A rapid assessment with the ultrasound probe can provide critical information; a subxiphoid view for cardiac contractility and evaluation of pericardial effusion, the IVC for preload assessment.  Perhaps you sweep by one of the costodiaphragmatic angles and find something like what’s shown in following video:

In the undifferentiated ill patient, the cause of the pleural effusion is not always clear. Is it secondary to decompensated CHF or is this a parapneumonic effusion? Obviously the clinical history and exam, imaging studies, (and perhaps the other sonographic views we mentioned), labs studies, etc that would lead you to the most likely conclusion. But…

Can bedside thoracic ultrasound diagnose a parapneumonic effusion?  Or are we doomed to google Light’s criteria once more and prepare for a rather uncomfortable bedside procedure?

It turns out that there have been a number of studies attempting to correlate the sonographic assessment of an exudative effusion and formal definition by Light’s criteria on thoracentesis.  While clinical decision rules have not been studied in large prospective trials, the following are some features of thoracic ultrasound that have been commonly used to classify pleural effusions as transudative or exudative in nature.

Transudates Features Exudate
No septations Anatomy Septations Septations present
Anechoic B-Mode Echogenicity Hypoechoic, heterogeneous internal echoes
< 3 mm Calipers Pleural thickness >3 mm

This is consistent with recommendations from 2012 that arose from the International Liaison Committee on Lung Ultrasound (more casually known as the ILC-LUS, of course).  Interestingly, of these characteristics, it turns out that echogenicity can be somewhat misleading.  While it would appear that the finding of internal echoes and/or hypoechoic fluid is highly suggestive of an exudative effusion, the absence of these findings does not guarantee that it is a transudate.  In one study, 14% of anechoic pleural effusions were eventually found to be exudates by pleural fluid analysis. Like many findings on POC ultrasound, finding Hypoechoic, heterogeneous internal echoes is specific for parapneumonic effusions, however not sensitive enough to exclude when the effusion is anechoic.

Based upon our newly found visual Light’s criteria, you might consider that the effusion in the video above is consistent with an exudative process based on the somewhat hypoechoic fluid with heterogenic echoes.  In the setting of presumed pneumonia, it might be reasonable to observe these expectantly based on guidelines from both the American College of Chest Physicians (ACCP) and American Thoracic Society (ATS) which describe characteristics of effusions that do not warrant immediate thoracentesis:

  • Effusions <10 mm thickness based on decubitus X-ray (surely a common order into today’s ED’s), CT, or thoracic ultrasound.
  • Free-flowing effusion, without evidence of loculations

Of course, if an effusion did not fit the criteria mentioned above, it would then be appropriate to perform thoracentesis.  And if one of the following characteristics were found, consider the placement of a small (<18 Fr) chest tube for drainage. (Luckily, only about 10% of all parapneumonic effusions will meet this criteria)

Consider placement of small chest tube:

A Anatomy Large (> ½ hemithorax), loculated effusions
B Bacteriology Positive gram-stain
C Chemistry pH <7.20

In the end, what started as a discussion of “things our attendings said in medical school” turned into a great review of a disease process for which we can do a great deal in the way of work-up quickly at the bedside.


  1. Sahn SA, Light RW. The sun should never set on a parapneumonic effusion. Chest. 1989;95(5):945-7.
  2. Muhammad S, Azam R, Owen W, Kamalanathan M, Toma T.  A simple score based on ultrasound criteria to distinguish between exudative vs. transudative pleural effusions. European Respiratory Journal. 2014.
  3. Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577-91.
  4. Sajadieh H, Afzali F, Sajadieh V, Sajadieh A. Ultrasound as an alternative to aspiration for determining the nature of pleural effusion, especially in older people. Ann N Y Acad Sci. 2004;1019:585-92.
  5. Marcun R, Sustic A. Sonographic evaluation of unexplained pleural exudate: a prospective case series. Wien Klin Wochenschr. 2009;121(9-10):334-8.
  6. Colice GL, Curtis A, Deslauriers J, et al. Medical and surgical treatment of parapneumonic effusions : an evidence-based guideline. Chest. 2000;118(4):1158-71.
  7. Light RW. Parapneumonic effusions and empyema. Proc Am Thorac Soc. 2006;3(1):75-80.
  8. Colice GL, Curtis A, Deslauriers J, et al. Medical and surgical treatment of parapneumonic effusions : an evidence-based guideline. Chest. 2000;118(4):1158-71.