Pleural Effusion in Children
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Direct answer
A pleural effusion is an abnormal collection of fluid in the pleural space, and in children a parapneumonic cause is common. Light's criteria classify the fluid as an exudate when its protein ratio, LDH ratio or LDH level meets set thresholds, separating infective and malignant effusions from transudates of heart failure or nephrotic syndrome. Chest tube drainage is indicated for empyema, loculated collections or complicated effusions that fail antibiotics.
What you must remember
- Light's criteria: an exudate if the pleural to serum protein ratio is above 0.5, the pleural to serum LDH ratio is above 0.6, or the pleural LDH is above two-thirds of the upper limit of normal serum LDH.
- Transudate: from heart failure, nephrotic syndrome or hypoalbuminaemia, and it fails all three exudate criteria.
- Parapneumonic effusion: complicates pneumonia, most often caused by pneumococcus, Staphylococcus aureus and Streptococcus pyogenes.
- Complicated effusion markers: pleural pH below 7.2, low glucose, high LDH, a positive Gram stain or culture, and loculation, with adult-derived thresholds often applied in children.
- Chest tube indications: frank pus or empyema, a positive Gram stain or culture, loculation, and a persistent effusion despite antibiotics.
- Chylothorax: milky fluid with high triglycerides, managed with dietary fat restriction and medium-chain triglycerides.
- Tuberculous effusion: a lymphocyte-predominant exudate with raised adenosine deaminase, most often in older children.
From a radiograph to a drainage decision
A 4-year-old has fever for five days after a pneumonia, and ultrasound shows a collection with septations. The steps below move from confirming the effusion to deciding on drainage, and each one depends on the fluid findings.
- Confirm the effusion. A chest X-ray shows blunting of the costophrenic angle, and ultrasound confirms the size, the presence of loculation and the best site for aspiration.
- Aspirate and send the fluid. Diagnostic thoracocentesis is sent for pH, glucose, LDH, protein, cell count, Gram stain and culture, with TB testing when indicated.
- Classify the fluid. Apply Light's criteria and the cell count, since neutrophil predominance points to infection and lymphocyte predominance points to tuberculosis or malignancy.
- Assess for complication. A pH below 7.2 or a loculated collection suggests the need for drainage, and frank pus confirms empyema.
- Drain when indicated. Tube thoracostomy is chosen when antibiotics alone fail, and it is sometimes combined with fibrinolytics in specialist centres.
- Treat the cause and follow up. Antibiotics are guided by culture and local resistance, and follow-up imaging confirms resolution.
Where the exam tries to catch you
Most questions here depend on reading the fluid numbers correctly.
- Trap: calling a heart-failure effusion an exudate Correct: transudates from heart failure or nephrotic syndrome fail Light's criteria, so the protein and LDH ratios stay low.
- Trap: draining every small free-flowing effusion Correct: small free-flowing parapneumonic effusions often resolve with antibiotics, and drainage is reserved for loculated, purulent or persistent collections.
- Trap: treating a milky effusion as an infection Correct: milky fluid with high triglycerides indicates chylothorax, which is managed with dietary fat restriction and medium-chain triglycerides.
Frequently asked questions
What are Light's criteria for a pleural exudate?
Light's criteria classify a pleural effusion as an exudate if the pleural to serum protein ratio is above 0.5, the pleural to serum LDH ratio is above 0.6, or the pleural LDH is above two-thirds of the upper limit of normal serum LDH. A pleural effusion meeting any one of these thresholds is an exudate.
When is chest tube drainage indicated in a parapneumonic effusion?
Chest tube drainage is indicated in a parapneumonic effusion when there is frank pus, a positive Gram stain or culture, loculation, or a persistent effusion despite appropriate antibiotics. Adult-derived thresholds such as a pleural pH below 7.2 are often used to guide drainage in children as well.
What causes a milky pleural effusion in a child?
A milky pleural effusion in a child is usually chylothorax, caused by leakage of lymph into the pleural space after cardiothoracic surgery, trauma or a congenital lymphatic defect. The diagnosis is confirmed by high triglyceride levels in the fluid, and treatment starts with dietary fat restriction and medium-chain triglycerides.
Which pleural fluid finding suggests tuberculosis in a child?
A lymphocyte-predominant exudate with a raised adenosine deaminase level suggests tuberculous pleural effusion in a child. Tuberculosis is more common in older children, and pleural biopsy or TB PCR may be needed when the diagnosis remains uncertain.