Part 2 · The Pleura

Pleural Effusion

Light's criteria, fluid analysis, and safe drainage — the foundation of pleural disease management.

PleuraSurgical relevance

Overview

A pleural effusion is an abnormal accumulation of fluid in the pleural space. Normally, the pleural space contains a thin film of fluid (~15 mL) maintained by a balance of hydrostatic, oncotic, and lymphatic forces. Disruption of any of these mechanisms leads to effusion.

Light's criteria — exudate vs transudate

An effusion is an exudate if any ONE of the following is met:
1. Pleural fluid protein / serum protein >0.5
2. Pleural fluid LDH / serum LDH >0.6
3. Pleural fluid LDH > two-thirds of the upper limit of normal serum LDH
If none are met, the effusion is a transudate.

Aetiology

Common causes of pleural effusion
TransudativeExudative
Congestive cardiac failurePneumonia (parapneumonic)
Mitral valve diseasePulmonary tuberculosis
Renal failure / peritoneal dialysisMalignancy (lung, mesothelioma, metastatic)
Hepatic cirrhosisChylothorax
Pulmonary embolismConnective tissue disorders (SLE, RA)
AtelectasisPancreatitis, oesophageal rupture
Meig's syndromeAsbestosis
Ovarian hyperstimulationDrug-induced (amiodarone, phenytoin, methotrexate)

Pleural fluid analysis

Chest X-ray showing massive left-sided pleural effusion with complete opacification of left hemithorax and mediastinal shift
Fig. 1. PA chest radiograph showing a massive left-sided pleural effusion — complete opacification of the left hemithorax with mediastinal shift to the right. The diaphragm is obscured and the effusion tracks up the lateral chest wall (meniscus sign). Via Wikimedia Commons. CC BY-SA 3.0.
Pleural fluid characteristics — transudate vs exudate
ParameterTransudateExudate
AppearanceClearCloudy / turbid
Spontaneous clottingNoYes
pH>7.37.0–7.2
Specific gravity1.012–1.019>1.020
WBC count<1000/µL>1000/µL
Protein<3 g/dL>3 g/dL
LDH<200 IU/L>200 IU/L
Fluid protein / serum protein<0.5>0.5
Fluid LDH / serum LDH<0.6>0.6
Cholesterol<45 mg/dL>45 mg/dL

Additional fluid tests by clinical context

  • ADA (>40 U/L) — strongly predictive for TB in high-prevalence areas
  • Cytology — positive in 60–70% of malignant effusions; sensitivity increases with repeat sampling
  • Glucose — low in RA, TB, empyema, malignancy, oesophageal rupture
  • Amylase — elevated in pancreatitis and oesophageal rupture
  • Triglycerides >110 mg/dL — chylothorax
  • Haematocrit >50% of peripheral blood — haemothorax

Investigations

  • Chest X-ray: blunting of costophrenic angle (≥200 mL); opacification with meniscus sign; mediastinal shift away from large effusions (shift towards suggests trapped lung or collapse)
  • Ultrasound: confirms effusion, characterises echogenicity, guides safe thoracentesis — mandatory before pleural procedures
  • CT thorax: identifies underlying parenchymal disease, nodal involvement, pleural thickening, loculations
  • Thoracentesis: diagnostic and therapeutic; guided by ultrasound; send fluid for biochemistry, culture, cytology
  • Pleural biopsy: closed (Abrams/Cope needle) or thoracoscopy-guided — thoracoscopy-guided biopsy gives near-100% yield for TB and malignancy

Treatment

Treatment is directed at the underlying cause. Symptomatic relief from the effusion itself is achieved by drainage.

  • Thoracentesis: diagnostic and therapeutic; limit drainage to 1–1.5 L per session to prevent re-expansion pulmonary oedema
  • Intercostal chest drain: for large or rapidly recurring effusions, empyema, or haemothorax
  • Indwelling pleural catheter (IPC): for recurrent or malignant effusions — patient-controlled drainage at home
  • Surgical drainage: VATS for complex effusions with loculations, failed catheter drainage, or planned biopsy
Safe thoracentesis

Always use ultrasound guidance — reduces pneumothorax rate from ~18% to <3%. Insert needle above the upper border of the lower rib to avoid the neurovascular bundle. Avoid the medial third of the intercostal space (intercostal nerve gives off a collateral branch that runs above the rib here). Stop if the patient develops chest tightness, cough, or vasovagal symptoms.

Further reading

All clinical content should be verified against current guidelines before clinical application. This resource is intended for revision and educational purposes only.

Standard textbooks

  • Shields TW, LoCicero J, Reed CE, Feins RH. General Thoracic Surgery. 7th ed. Lippincott Williams & Wilkins.
  • Sellke FW, del Nido PJ, Swanson SJ. Sabiston & Spencer Surgery of the Chest. 9th ed. Elsevier.
  • Pearson FG, et al. Thoracic Surgery. 3rd ed. Churchill Livingstone.

Current guidelines & resources