Pleural Space

Question 1

The clinical importance of the pleural space in pleural effusion

Answer 1

-Pleural space: negative pressure
-As pleural fluid collects in the space, the pressure changes and becomes positive
-Changes again when fluid is drained out of lung; pressure change can cause cough and chest pain/ tightness

Question 2

What can accumulate in the pleural space?

Answer 2

-Air: PTX
-Proteinaceous fluid: exudative pleural effusion
-Protein deficient fluid: transudative pleural effusion
-Blood: haemothorax
-Chyle (fluid from lymphatic system): Chylothorax
-Fluid and air: hydropneumothorax
-Pus: empyema
-Tumour: primary or secondary (benign or malignant)
-Asbestos fibres: pleural plaque disease

Question 3

Physiology of pleural fluid accumulation

Answer 3

• Increased interstitial fluid in lung (LVSD, CAP, PTE)
• Increased intravascular pressure in the pleura (LVSD, SVCO, RVF)
• Increased permeability of the capillaries in the pleura (Inflammation)
• Increased pleural fluid protein level
• Decreased pleural pressure (Lung atelectasis)
• Increased fluid in peritoneal cavity (ascites, PD)
• Disruption of the thoracic duct (iatrogenic, haem malignancy)
• Disruption of thoracic blood vessels (iatrogenic, trauma)
• Obstruction of lymphatics draining parietal pleura (malignancy)
• Elevation of systemic vascular pressures SVCO, RVF)

Question 4

Exudate vs transudate

Answer 4

-Exudate: high protein content (>30g/L)
-Transudate: low protein content (<30g/L)- organ failure, usually bilateral and smaller
-More specifically the Light’s criteria however misclassify 25% transudates as exudates

Question 5

Describe the Light’s criteria

Answer 5

Exudate diagnosed if 2 of:
-Pleural to serum protein ratio >0.5
-Pleural to serum LDH ratio >0.6
-Pleural LDH >2/3 upper limit normal (>145)
IN THE RIGHT CLINICAL CONTEXT

Question 6

Common causes of exudate pleural effusion

Answer 6

-Parapneumonic
-Malignancy

Question 7

Less common causes of exudate pleural effusion

Answer 7

-Tuberculosis
-PE/infarction
-Rheumatoid arthritis
-SLE
-Pancreatitis
-Benign asbestos
effusion
-Post MI/CABG

Question 8

Very rare causes of exudate pleural effusion

Answer 8

-Yellow nail syndrome
-Drugs (amiodarone, methotrexate)

Question 9

Common causes of transudate pleural effusion

Answer 9

-Heart failure
-Liver failure

Question 10

Less common causes of transudate pleural effusion

Answer 10

-Hypalbuminaemia
-Nephrotic syndrome
-Peritoneal dialysis

Question 11

Very rare causes of transudate pleural effusion

Answer 11

-Hypothyroidism
-Constrictive pericarditis
-Meigs syndrome

Question 12

Investigations of pleural effusions

Answer 12

• Imaging: CXR, USS, CT (PET/MRI experimentally)
• Pleural aspiration (60ml syringe, green needle, USS)
• Appearance/Odour?
  – Biochemistry: protein, glucose, LDH, pH (10ml)
  – Microbiology: bacteriology (Blood culture bottles),
  AAFB/mycobacterial culture (20ml-60mls)
  – Pathology: cytology (60% sensitivity) 60-200ml
• Repeat aspiration?
• Medical thoracoscopy vs VATS

Question 13

Added diagnostic information of USS

Answer 13

-Echogenic fluid
-Septations
-Pleural thickening
-Pleural/ diaphragmatic nodularity

Question 14

Likely cause of frank pus effusion

Answer 14

Empyema

Question 15

Likely cause of blood-stained effusion

Answer 15

-Malignancy
-Pulmonary infraction
-Post cardiac injury syndrome
-Infection
-TB

Question 16

Likely cause of frank blood effusion

Answer 16

Haemothorax

Question 17

Likely cause of milky effusion

Answer 17

Chylothorax (due to thoracic duct disruption)

Question 18

Likely cause of food particle effusion

Answer 18

Oesophageal rupture

Question 19

Likely cause of bile stained effusion

Answer 19

Biliary fistula (biliothorax)

Question 20

Pleural fluid characteristic tests

Answer 20

-pH (low in pleural infection, RhA, malignancy)
-Protein
-LDH (high malignancy, infection, inflammation)
-Glucose (very low in empyema, RhA)
-Triglycerides (chylothorax: >1.24mmol/L)
-Cholesterol (>5.18mmol/l in pseudochylothorax)
-Haematocrit (blood-stained vs frank blood)
-Amylase (oesophageal rupture, pancreatitis)