Write a short note on pleural effusion.

Definition

Abnormal accumulation of fluid in the pleural space. Normally 5–15 mL lubricates the pleural surfaces. About 500 mL is needed to blunt the costophrenic angle on an erect film, while ultrasound detects as little as 50 mL — which is why ultrasound is now standard.

Clinical Features

• Breathlessness, pleuritic pain (often preceding the effusion and easing as fluid separates the layers), dry cough
• Affected side: reduced expansion, STONY DULL percussion, DIMINISHED OR ABSENT BREATH SOUNDS, reduced vocal fremitus and resonance, and trachea and mediastinum shifted AWAY if large
• Bronchial breathing and egophony at the UPPER LEVEL from compressed lung
• Features of the cause — fever, weight loss and clubbing, orthopnoea and raised JVP, stigmata of liver disease

Light's Criteria

The fluid is an EXUDATE if ANY ONE is met:

1. Pleural : serum PROTEIN ratio > 0.5

2. Pleural : serum LDH ratio > 0.6

3. Pleural LDH > two-thirds of the upper limit of normal serum LDH

Sensitivity for exudates is ~98%, but about 25% of TRANSUDATES are misclassified as exudates — most often heart failure patients on DIURETICS, which concentrate the protein. Then use the serum–pleural ALBUMIN GRADIENT > 1.2 g/dL to identify a transudate.

Investigations

• Chest X-ray — blunting of the costophrenic angle, homogeneous opacity with a MENISCUS; massive effusion opacifies the hemithorax with mediastinal shift AWAY (shift towards indicates collapse, not effusion)
• ULTRASOUND — the investigation of choice: detects small effusions, identifies septations and loculation, and should guide every aspiration
• CT with contrast — parenchymal disease, malignancy, pleural thickening and nodularity, "split pleura" sign of empyema

DIAGNOSTIC PLEURAL ASPIRATION — mandatory for any undiagnosed effusion. Send for:

Pleural biopsy — Abrams' or image-guided for suspected TB (culture the biopsy, which raises yield); THORACOSCOPY with direct biopsy is the gold standard for undiagnosed exudates (yield > 90%).

Specific Entities

Tuberculous effusion — the commonest exudative effusion in young Indian adults: unilateral, lymphocytic, high protein, low glucose, raised ADA, and smear-negative with low culture yield. Treat with antitubercular therapy; drain only if large and symptomatic.

Parapneumonic effusion and empyema — simple (sterile, pH > 7.2 — antibiotics alone); complicated (pH < 7.2, glucose < 60 — requires drainage); empyema (frank pus — drainage plus antibiotics, with intrapleural tPA and DNase for loculation and surgical decortication for failure).

CHYLOTHORAX — milky fluid with triglycerides > 110 mg/dL and chylomicrons, from thoracic duct disruption:

• malignancy (lymphoma — commonest), trauma or surgery, tuberculosis and filariasis (relevant in India). Causes loss of protein, fat, fat-soluble vitamins and lymphocytes with malnutrition and immunosuppression.
• Management: treat the cause
• medium-chain triglyceride diet or TPN
• drainage
• octreotide
• thoracic duct ligation or embolisation. Distinguish from pseudochylothorax (chronic tuberculous or rheumatoid effusion — high cholesterol with crystals, low triglycerides).

Management

1. Treat the cause — diuretics, antitubercular therapy, antibiotics, management of malignancy

2. Therapeutic aspiration — remove no more than 1–1.5 litres at a sitting to avoid re-expansion pulmonary oedema

3. Intercostal drain for empyema, complicated parapneumonic effusion, haemothorax and large symptomatic malignant effusions

4. Recurrent malignant effusion: talc pleurodesis or an indwelling pleural catheter (often preferable with limited life expectancy)

5. Surgery — decortication for trapped lung or failed drainage