Orientation notes for study. Check local guidelines before prescribing or performing procedures.
Definition
A pleural effusion is an abnormal collection of fluid in the pleural space (between the visceral and parietal pleura). Normally only 5–15 mL of fluid is present.
Mechanisms
- Increased hydrostatic pressure (heart failure) → transudate.
- Decreased oncotic pressure (low albumin) → transudate.
- Increased capillary permeability or inflammation (infection, cancer) → exudate.
- Impaired lymphatic drainage (malignancy) → exudate.
- Fluid passing from the abdomen (ascites, peritoneal dialysis) → transudate.
Causes: transudate versus exudate
| Transudate (protein below 30 g/L) | Exudate (protein above 30 g/L) |
|---|---|
| Heart failure (commonest, bilateral) | Pneumonia (parapneumonic effusion, empyema) |
| Cirrhosis (hepatic hydrothorax) | Tuberculosis (very common in Kenya, HIV) |
| Nephrotic syndrome, hypoalbuminaemia | Malignancy (lung, breast, lymphoma, mesothelioma, metastases) |
| Hypothyroidism | Pulmonary embolism |
| Peritoneal dialysis | Rheumatoid arthritis, SLE |
| Meigs syndrome | Pancreatitis, oesophageal rupture |
| Constrictive pericarditis | Asbestos-related, drugs (amiodarone, nitrofurantoin) |
Light's criteria (an exudate if ANY one is met)
- Pleural fluid protein / serum protein above 0.5
- Pleural fluid LDH / serum LDH above 0.6
- Pleural fluid LDH above two-thirds of the upper limit of the normal serum LDH
Clinical features
- Symptoms: progressive dyspnoea, pleuritic chest pain (may disappear as fluid separates the pleura), dry cough; plus symptoms of the cause (fever, weight loss, orthopnoea).
- Signs: stony dull percussion, reduced or absent breath sounds, reduced tactile vocal fremitus over the effusion; bronchial breathing at the upper edge; trachea and mediastinum pushed away if large; reduced chest expansion.
Investigations
- Chest X-ray: blunting of the costophrenic angle (needs about 200 mL on PA view), meniscus sign; large effusion causes "white-out" with contralateral shift.
- Ultrasound: confirms fluid, shows septations, and guides aspiration.
- CT chest: pleural thickening, nodules, masses, loculation.
- Diagnostic pleural aspiration (thoracentesis): send for
- Appearance (clear straw, bloody, pus, milky).
- Protein and LDH (Light's criteria), glucose (low in TB, rheumatoid, empyema, malignancy), pH (below 7.2 suggests empyema needing drainage).
- Cell count and differential: neutrophils (acute infection), lymphocytes (TB, cancer).
- Cytology (malignant cells), culture and Gram stain, AFB and GeneXpert, ADA (adenosine deaminase) high in TB.
- Triglycerides (chylothorax), amylase (pancreatic).
- Pleural biopsy (image-guided or thoracoscopic) if the diagnosis is still unclear.
- Treat the cause: echocardiography, LFTs, albumin, urine protein.
Management
- Treat the underlying cause: diuretics for heart failure, anti-TB treatment, antibiotics for infection, chemotherapy for cancer.
- Therapeutic aspiration for symptom relief (ultrasound-guided, stop at about 1.5 L or when the patient coughs or has chest tightness, to avoid re-expansion pulmonary oedema).
- Parapneumonic effusion and empyema: antibiotics plus chest drain if pus, pH below 7.2, positive Gram stain or culture, or loculation; fibrinolytics or surgical decortication if it fails.
- Malignant effusion: repeated aspiration, pleurodesis (talc) or an indwelling pleural catheter for recurrent effusions; treat the cancer.
- TB pleurisy: full anti-TB regimen; effusion usually resolves.
- Avoid sedatives in large effusions; oxygen if hypoxic.
Complications
- Empyema, pleural thickening and fibrosis (trapped lung), respiratory failure, re-expansion pulmonary oedema, pneumothorax and bleeding from aspiration.
Exam points
- Transudate = systemic (heart, liver, kidney); exudate = local pleural or lung disease.
- Light's criteria separates them.
- Low pleural glucose points to TB, rheumatoid, empyema, malignancy.
- pH below 7.2 needs a chest drain.
- Lymphocytic, high ADA effusion in Kenya: think TB.
- Always aspirate under ultrasound guidance.
Pharmacology at a glance
Tap a drug name for its full card (how it works, adverse effects, cautions, dose), then use Back to this note to return to this spot.
| Drug | Class | Role here | Watch for |
|---|---|---|---|
| Furosemide | Loop diuretic | Effusion from heart failure | Low potassium and sodium, dehydration |
| Rifampicin | Anti-TB drug | Tuberculous pleural effusion, as part of the standard regimen | Hepatitis, orange urine, many interactions |
| Ceftriaxone | Third-generation cephalosporin | Parapneumonic effusion and empyema | Biliary sludge, allergy |
| Metronidazole | Nitroimidazole | Anaerobic cover in empyema | Metallic taste; no alcohol |
| Paracetamol | Analgesic | Pleuritic pain | Liver injury in overdose |
Drain, do not just drug: a pleural pH below 7.2, pus or a positive culture needs a chest drain as well as antibiotics.
Practice questions
1. A 45-year-old woman with HIV has fever, weight loss and a unilateral effusion: protein 52 g/L, lymphocytes predominant, glucose low, ADA high. The most likely diagnosis is: A. Heart failure · B. Tuberculous pleural effusion · C. Nephrotic syndrome · D. Cirrhosis · E. Pulmonary embolism Answer: B.
2. A pleural fluid pH of 6.9 with a positive Gram stain in a patient with pneumonia should be treated with: A. Diuretics · B. Antibiotics and an urgent chest drain · C. Observation · D. Steroids · E. Talc pleurodesis Answer: B. Empyema.
3. Which finding classifies a pleural effusion as an exudate? A. Pleural LDH/serum LDH 0.4 · B. Pleural protein/serum protein 0.7 · C. Pleural protein 20 g/L only · D. Clear fluid · E. Bilateral effusions Answer: B.