Parapneumonic effusion and empyema !

A parapneumonic effusion is fluid around the lung during pneumonia; when it becomes infected or turns to pus it is called empyema and needs drainage.

Updated 2026-11-01

Structures involved

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In the clinical exam

Pleural effusion syndrome

Why it happens

What it is

A pleural effusion that develops next to a bacterial pneumonia or lung abscess. It may be simple (sterile exudate), complicated (bacteria invade the pleural space, pH and glucose fall) or frank empyema (pus in the pleural space).

Who gets it

Parapneumonic effusions appear in a large share of patients admitted with bacterial pneumonia, and a small fraction progress to empyema. Empyema is more common in children, older adults, people with alcohol use disorder, diabetes or poor dental health. In Colombia and Latin America tuberculous pleural effusion is an important alternative cause of exudate that must be considered.

Causes

Bacterial pneumonia (Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus anginosus group)
Anaerobic and mixed oral flora after aspiration or with a lung abscess
Gram-negative bacilli in hospital-acquired pneumonia
Chest trauma, thoracic surgery or pleural procedures
Spread from a subphrenic abscess or oesophageal rupture

Risk factors

Delayed treatment of pneumonia
Aspiration risk: alcohol use disorder, reduced consciousness, dysphagia
Diabetes mellitus and immunosuppression
Poor dental hygiene
Older age and chronic lung disease

Pathophysiology

Develops in three stages. In the exudative stage, inflammation makes the pleura leaky and sterile fluid accumulates. In the fibrinopurulent stage, bacteria invade, neutrophils and fibrin accumulate, pleural fluid pH and glucose fall and loculations form. In the organising stage, fibroblasts create a thick pleural peel that traps the lung and limits its expansion.

Classification

Simple (uncomplicated) parapneumonic effusion: free-flowing, sterile, pH 7.20 or higher
Complicated parapneumonic effusion: pH below 7.20, low glucose, high LDH or positive Gram stain or culture
Empyema: frank pus in the pleural space
Stages: exudative, fibrinopurulent, organising

Symptoms and signs

Fever persisting or returning despite treatment of pneumonia
Pleuritic chest pain that worsens with breathing
Shortness of breath and cough
Dullness to percussion, reduced breath sounds and reduced tactile fremitus on the affected side
Night sweats, weight loss and malaise in subacute cases

Diagnosis

Clinical: Suspected in a patient with pneumonia whose fever or pain persists, with signs of an effusion on examination. Every effusion of significant size in a patient with pneumonia is sampled.
Tests: Diagnostic thoracentesis is the key test: appearance, pH, glucose, LDH, protein, cell count, Gram stain and culture; Light criteria confirm an exudate. Pus, pH below 7.20 or a positive Gram stain or culture indicate the need for drainage. Blood cultures, blood count and C-reactive protein; adenosine deaminase and mycobacterial testing when tuberculosis is possible.
Imaging: Chest X-ray (blunted costophrenic angle, meniscus sign); pleural ultrasound to detect small effusions, septations and to guide the needle; contrast CT shows thickened, enhancing pleura (split pleura sign) and loculations.

Differential diagnosis

Tuberculous pleural effusion
Malignant pleural effusion
Heart failure transudate
Pulmonary embolism with effusion
Lung abscess with air-fluid level

Goal of treatment

Control the infection, drain the pleural space completely and allow the lung to re-expand before a fibrous peel forms.

Treatment

Medical: Prolonged intravenous then oral antibiotics covering the likely organisms, including anaerobes in community-acquired cases (e.g. a beta-lactam with beta-lactamase inhibitor).
Procedure: Chest tube drainage for empyema or complicated effusion, usually ultrasound-guided; intrapleural fibrinolytic plus DNase therapy for loculated collections.
Surgical: Video-assisted thoracoscopic surgery (VATS) debridement, or open decortication for an organised peel that traps the lung.
Follow-up: Nursing care: chest drain function and output, temperature curve, oxygen saturation, pain control and early mobilisation with breathing exercises.

Complications

Trapped lung and fibrothorax with restrictive defect
Bronchopleural fistula
Empyema necessitans (pus tracking through the chest wall)
Sepsis and death
Prolonged hospital stay

Prognosis

Most patients recover fully with antibiotics and adequate drainage. Mortality rises with older age, comorbidity, hospital-acquired infection and delayed drainage.

Prevention

Early diagnosis and treatment of pneumonia
Pneumococcal and influenza vaccination
Good dental hygiene and measures that reduce aspiration

Test yourself

Think of the answer, then tap the question to see it.

Which pleural fluid pH suggests a complicated parapneumonic effusion that needs drainage?

A pH below 7.20, especially with low glucose, high LDH or a positive Gram stain or culture.

What defines empyema?

The presence of frank pus, or organisms on Gram stain, in the pleural space.

What are the three stages of empyema?

Exudative, fibrinopurulent (bacteria, fibrin, loculations) and organising (fibrous peel that traps the lung).

Besides antibiotics, what is the cornerstone of empyema treatment?

Drainage of the pleural space, usually with a chest tube; thoracoscopic surgery or decortication if drainage fails or a peel forms.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Empyema (MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

Pleura highlighted on the Durgical 3D model