Assessing patients with pleural effusions in the emergency department (ED) can be challenging and unclear. This is largely due to the lack of guidelines around pleural effusions in the ED. In this post, I’ve tried to highlight some key information about an approach to patients presenting with a new pleural effusion. This is not all-encompassing, but an attempt at an approach.
Stay tuned for part 2 where we will focus on Malignant and CHF-related effusions and how to optimize the thoracentesis.
The main objectives are as follows:
- To classify and characterize pleural effusions on POCUS and pleural fluid analysis
- To outline the diagnostic approach to and management of
- Parapneumonic,
- Malignant, and
- CHF-related pleural effusions
- To describe the types of parapneumonic effusions and their specific management
- To optimize the ED thoracentesis procedure
Categories of Pleural Effusions
There are many different causes of pleural effusions. The cause is often classified initially as transudative or exudative. Listed below are some common and less common causes of effusions in each category.
Transudative effusions stem from any imbalance between the hydrostatic and oncotic pressures. In transudative effusions, the pleura itself is not diseased. The most common cause is heart failure (CHF).
Exudative effusions result from direct involvement or disease of the pleura. Impaired lymphatic drainage and increased capillary permeability lead to the buildup of exudative effusions. The primary causes are infections and malignancies.
The diagnostic and therapeutic implications of transudates vs exudates differ, which is why distinguishing these two types is important.
In this 2 part series, we will review 3 cases highlighting common presentations and etiologies of pleural effusions:
- Mr. PPE (parapneumonic effusions)
- And Ms. MPE (malignant pleural effusions)
- Ms. CHF (congestive heart failure-related effusions)
But first, we’ll begin with an approach to the diagnosis of a pleural effusion.
Diagnosis of a Pleural Effusion
In terms of work-up, the integration of clinical features, imaging, and pleural fluid analysis is needed to characterize and diagnose effusions, and to ensure timely and appropriate management.
Imaging Assessment of Pleural Effusions
Chest X-Ray
Standard chest x-rays are often the initial imaging modality obtained in the ED. Important features to note on chest x-ray is whether the effusion is unilateral or bilateral, the general size of the effusion, and the presence or absence of other diagnostic findings (pneumonia, lung mass). On PA x-rays, effusions are first seen when the volume approaches 200mL. This appears as blunting of the costophrenic angle. Chest x-ray is a valuable first step, but point-care-ultrasound (POCUS) and CT chest are more sensitive for the detection and characterization of pleural fluid.
Radiopedia.org Pleural Effusion.
Jones 2009, updated Sharma 2024
PoCUS
We should be assessing ALL patients with a symptomatic new effusion with POCUS. POCUS can help to further characterize effusions and provide information to guide further work-up. Ultrasound is highly sensitive for detecting a pleural effusion. A recent meta-analysis by Zaki et al. in 2024 showed that POCUS had a higher sensitivity and diagnostic accuracy compared to CXR.
Assessing the size of an effusion with POCUS is important when considering the need for pleural drainage. There are different methods for pleural effusion size and volume assessment that are reviewed in the literature. Two notable methods are as follows:
1. Interpleural distance
- Measure the distance between the parietal and visceral pleura at the base of the lung. For most etiologies of pleural effusions, if the distance <10mm, the effusion is generally not clinically significant and further work-up is not needed
Mirza et al. 2021 Thoracentesis Sonoguide ACEP
2. Lung-diaphragm distance
- Assess the distance between the lung base and the mid-diaphragm. By this second method, we can estimate effusion size using categories of small (approximately <500mL), moderate (500-1000mL), or large volume (>1000mL)
Adapted from Brogi et al. 2027
Based on POCUS characteristics, pleural effusions can be categorized as:
1) Simple (free-flowing), or
2) Complicated
Unfortunately, it has been shown that anechoic fluid alone cannot reliably differentiate transudates from exudates. A complicated effusion is defined as any significant echogenic finding. This echogenicity makes the diagnosis of an exudate much more likely. Significant echogenic findings of complicated effusions can include:
- Septations
- Pleural Thickening
- Thick Cellular Debris or Homogenous Echogenicity
Take-Home Points for Initial Imaging of Effusions
- POCUS can provide a good estimation of effusion size. This information can dictate the need for further work-up and guidance for thoracentesis.
- Simple effusions with an interpleural distance <10mm are generally not considered significant for us in the ED
- Echogenic findings define a complicated effusion. This makes the diagnosis of an exudate much more likely
- This information can quickly impact a patient’s management
Parapneumonic Effusions
Case 1
Mr. PPE is a 52 year-old man presenting with a fever, productive cough and shortness of breath for the past one-week. He is tachypneic and tachycardic in the ED. He has crackles and decreased air entry to his left lung. His chest x-ray and POCUS both show a moderate-sized left-sided consolidation and effusion.
Dinh V. Lung Ultrasound Made Easy POCUS 101
What is a parapneumonic effusion?
A parapneumonic effusion (PPE) is a pleural effusion associated with suppurative parenchymal lung disease (such as bacterial pneumonia or a lung abscess). Parapneumonic effusions are seen in approximately 40-50% of bacterial pneumonia. The vast majority of parapneumonic effusions, however, are small and resolve with antibiotic therapy alone. Of patients hospitalized with a parapneumonic effusion, 5-10% progress to an empyema.
There are different types of PPEs that are important for us to know:
- Non-clinically significant PPE: an effusion that is simple, small and approximately less than 10mm on POCUS or CT. Generally, no further work-up is needed.
- Uncomplicated PPE: a sizeable pleural effusion (>10mm) where the pleural fluid itself is not infected.
Over time, as a pneumonia and effusion progress, the pleural fluid becomes a substrate for bacterial invasion and growth. This can lead to:
- Complicated PPE: an infected pleural effusion
- Complex complicated PPE: an infected effusion with loculations
- Empyema: purulent pleural fluid or frank pus in the pleural cavity
Recognition of infected PPEs is crucial. Even with appropriate treatment, the mortality of patients with empyema is as high as 15%. The incidence of empyema is rising, especially in pediatric populations. The wider use of immunosuppressants and the increasing age of the population means pleural infection will continue to remain significant.
1. Non-Significant Parapneumonic Effusion
A non-significant parapneumonic effusion is the type most commonly seen in the ED. They will often be found incidentally when assessing for pneumonia. These effusions are simple, small (<10mm) and do not require further work-up. Treatment involves treating the pneumonia with antibiotics as per typical practice.
Diagnostic Thoracentesis
In the case of Mr. PP, there is a moderately-sized pleural effusion in the context of his pneumonia. Does he require a thoracentesis? Guidelines (American Association for Thoracic Surgery 2017, British Thoracic Society 2023) and experts in the field have suggested that a diagnostic thoracentesis is clinically indicated in symptomatic patients: especially in those patients with infectious symptoms and a new, accessible pocket of pleural fluid.
When discussing an ‘amenable pocket’ for diagnostic thoracentesis, although there is no clear definition, we should essentially be evaluating for three main factors:
- Pleural fluid size or volume
- At least a moderate-sized pocket
- Free-flowing Effusion
- M-mode on POCUS can be useful here. If there is absence of lung movement within the pleural effusion, this may represent a pleural mass and we should not proceed with a thoracentesis, pending further imaging.
- Absence of locations in the effusion
M-Mode
For the patient Mr. PPE, there is a homogenous hyperechoic effusion and an amenable pocket for sampling. You proceed with the diagnostic thoracentesis.
Pleural Fluid Analysis and Classification
Despite the utility of imaging, pleural fluid sampling and analysis is essential for a definitive diagnosis of the etiology of a pleural effusion. Pleural fluid should be sent for the following:
- Cell count and differential
- Gram stain
- Aerobic and anerobic cultures
- pH
- Protein
- Glucose
- LDH
Conventionally, the workup of a pleural effusion begins broadly by triaging effusions as transudates or exudates.
Light’s Criteria
Light’s criteria is the classic method for classifying pleural effusions and distinguishing a transudate from an exudate. Light’s criteria has a high sensitivity and this aims to prioritize the diagnosis of exudates. Specifically, Lights’ criteria has a 94.7% accuracy rate in predicting exudates.
Pleural Fluid pH
Pleural fluid pH can provide additional useful information in the work-up of pleural effusions. Notably, decreased pH levels caused by inflammatory mediators and bacteria are typically seen in exudative effusions, such as those associated with pneumonia, malignancy and tuberculosis. Pleural fluid pH can also help with the classification of parapneumonic effusions. For these effusions, decreased fluid pH is characteristic of complicated parapneumonic effusions. Studies have shown that a pH of 7.2 is an accurate discriminator of infected (<7.2) and noninfected (>7.2) effusions.
2. Uncomplicated Parapneumonic Effusion
The features of an uncomplicated parapneumonic effusion include:
- Effusion size >10mm (differentiates from a non-significant effusion)
- pH > 7.2
- Glucose > 2.2 + LDH < 1000
The treatment involves antibiotics for typical pneumonia therapy. The vast majority of patients will have a good response to antibiotic treatment. Patients who are stable with biochemistry that meets the above criteria can be discharged home with antibiotics. The exceptions are those patients with a large or a persistently moderate-to-large effusion: in these cases, local respirology specialists should be consulted.
A therapeutic thoracentesis can also be considered depending on the size of the effusion and the patient’s symptoms/ dyspnea.
Case 1- Mr. PPE’s pleural fluid analysis is consistent with an exudative effusion and an uncomplicated PPE with a pH of 7.5. He has a therapeutic thoracentesis given his dyspnea and moderate-sized effusion. He receives treatment for community-acquired pneumonia and is discharged home with appropriate follow-up.
The majority of sizeable parapneumonic effusions seen and managed in the ED will be similar to this case of Mr. PPE.
3. Complicated Parapneumonic Effusion
Let’s consider an alternative scenario for Mr. PPE: he has now had two weeks of persistent cough, fever and pleuritic chest pain. He finally presents to ED because his symptoms are worsening. He is ill-appearing in the ED with increased work-of-breathing. He has a consolidation and a moderate-sized effusion. His pleural fluid analysis shows:
- pH of 7.1
- Glucose of 2.1 and LDH of 1100
This represents a complicated or infected parapneumonic effusion. Infected effusions should be suspected in all patients with PNA, particularly in patients who are:
- Elderly,
- Immunosuppressed, or
- Who fail to respond to appropriate antibiotic therapy.
Complicated parapneumonic effusions can present later in the course of pneumonia as the effusion progresses and bacteria invade the pleural fluid.
The features of a simple complicated parapneumonic effusion include:
- pH < 7.2
- Glucose < 2.2 and LDH > 1000
The treatment involves antibiotics as well as a surgical consultation for consideration of a small-bore chest tube, as these effusions are less likely to improve with antibiotics alone.
4. Complex Parapneumonic Effusion
In a complex parapneumonic effusion, the infection within the pleural cavity causes characteristic septae-producing loculations. The loculations make it more difficult to find an amenable pocket for pleural fluid sampling via thoracentesis in the ED. When loculations are seen on POCUS, a CT is often a helpful next step in order to further characterize a complex parapneumonic effusion. Loculations in the setting of a parapneumonic effusion are associated with a complicated clinical course, including higher ICU admission rates and a higher mortality rate. Complex infected effusions also require a surgical consultation for consideration of a small-bore chest tube, as well as for additional therapies such as fibrinolytics.
5. Empyema
CT
An empyema is purulent pleural fluid or frank pus in the pleural cavity. There are certain features on a CT that can identify an empyema (specifically a pleural split-sign). If these CT characteristic features are present for a loculated parapneumonic effusion, this is an indication for a surgical consultation. It is important to note that a CT is not otherwise diagnostic of an infected parapneumonic effusion; it does not replace pleural fluid analysis.
Radiopedia.org. Empyema. Venkatesh 2016.
Pleural Aspiration
Aspiration of frank pus via thoracentesis (if an amenable pocket on POCUS) is diagnostic of an empyema. Diagnosis of an empyema then requires a surgical consultation for placement of a small-bore chest tube as well as consideration for additional therapies (fibrinolytics, decortication).
Indications for Surgical Consultation and Tube Thoracostomy in Parapneuonic Effusion
- Pleural fluid pH < 7.2 with suspected pleural space infection
- Pleural fluid LDH >1000 IU/L + glucose <3.3mmol/L (if pH not available) with suspected pleural space infection
- Loculated effusions
- CT features of an empyema
- Aspiration of frank pus
- Positive gram stain and culture
These findings suggest that the effusion is unlikely to resolve with antibiotics alone, and tube thoracostomy (with consideration of additional therapies) is recommended.
Management of Parapneumonic Effusions, a Summary:
All patients with PPEs need to be treated with appropriate antibiotics for pneumonia coverage. The initial selection is based on whether the infection is community- or hospital-acquired. Additional therapeutic interventions will be considered by thoracic surgery or surgical experts as needed. This can include, for example: specialized CT-guided small-bore chest tube insertion, pleural fibrinolytics, among others.
Parapneumonic Effusion Take-Home Points
- Appropriate work-up is required for a new pleural effusion with an amenable pocket in the setting of pneumonia.
- Fluid analysis and appropriate imaging of a parapneumonic effusion has important clinical consequences with respect to management and disposition. For example, this information can dictate whether a patient is discharged home with antibiotics, or an in-hospital consultation is required to respirology or thoracic surgery for ongoing therapy.
- Indications for surgical consultation for consideration of a small-bore chest tube:
- pH < 7.2
- Loculated PPE
- Empyema on CT
- Frank pus
Stay tuned for part 2 where we will discuss malignant pleural effusions, and tips and tricks for the thoracentesis in the ED!
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*The POCUS images in this post were captured and shared by:
Dr. Rajiv Thavanathan, MD FRCPC, Emergency Physician, Department of Emergency Medicine, The Ottawa Hospital, Assistant Program Director | Area of Focused Competency POCUS.
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