Are Pleural Effusions Common After Pneumonia?
Yes, pleural effusions are very common after pneumonia, occurring in approximately 40% of hospitalized patients with bacterial pneumonia. 1, 2
Incidence and Clinical Significance
Pleural effusions complicate 40-44% of all cases of bacterial pneumonia requiring hospitalization, making them one of the most frequent complications of pneumonic illness 1, 2, 3
The actual prevalence may be even higher, as small parapneumonic effusions are often undetected and underreported in clinical series, with some estimates suggesting up to 40% of all pneumonia cases admitted to hospital develop effusions 4, 1
While effusions are common, only a minority progress to complicated parapneumonic effusions or empyema requiring intervention (approximately 5-10% of those with effusions) 2
When to Suspect a Parapneumonic Effusion
If a patient remains febrile or unwell 48 hours after admission for pneumonia, parapneumonic effusion must be actively excluded through careful clinical examination and repeat chest radiography 4
Key Clinical Presentations:
Patients with effusions are typically more unwell than those with simple pneumonia alone, presenting with persistent high fever despite appropriate antibiotic therapy 4, 5
Physical examination reveals unilateral decreased chest expansion, dullness to percussion, reduced or absent breath sounds, and possibly scoliosis 4, 5
Pleuritic chest pain is common, and patients may lie on the affected side to splint the hemithorax 4
Diagnostic Approach
Chest radiography should be obtained, looking for obliteration of the costophrenic angle (earliest sign) or a meniscus sign of fluid ascending the lateral chest wall 4
Ultrasound must be used to confirm the presence of pleural fluid and should guide any thoracentesis or drain placement 4
All parapneumonic effusions should be aspirated for diagnostic purposes to determine if drainage is required, which may need image guidance if the effusion is small or loculated 6
Management Implications
The presence of a pleural effusion significantly increases morbidity and mortality compared to pneumonia alone 6, 2, making early recognition and appropriate management critical for optimal outcomes.
Effusions Requiring Drainage:
According to current guidelines, drain any parapneumonic effusion meeting at least one of these criteria: 6
- Size ≥ 1/2 of the hemithorax
- Loculations present
- Pleural fluid pH < 7.20 (or glucose < 60 mg/dl)
- Positive Gram stain or culture
- Purulent appearance
Effusions Managed Conservatively:
Small effusions (<10mm rim on imaging) can be treated with antibiotics alone without drainage 7
Uncomplicated effusions with pH > 7.20 and LDH < 1,000 IU/L rarely require intervention and typically resolve with appropriate antibiotic therapy 3
Prognosis
The prognosis in children with empyema is usually very good, with the majority making complete recovery and lung function returning to normal 4. Chest radiographs return to normal in 60-83% by 3 months, over 90% by 6 months, and all by 18 months 4.