Pleural diseases

Question 1

Describe how a pleural effusion occurs

Answer 1

Hydrostatic pressure is the main cause of pleural effusion – pushing fluid into the pleural space – taken up by oncotic proteins in plasma and by the lymphatic system (when this system is overloaded -> pleural effusion)

Question 2

List the causes of a pleural effusion

Answer 2

• Increased hydrostatic pressure
• Decreased plasma oncotic pressure
• Increased vascular or pleural permeability (e.g. inflammation).
• Increased fluid production (e.g. infection).
• Lymphatic capacity can increase 30x if required.

Question 3

How does a pleural effusion appear on a radiograph?

Answer 3

Effacement of the cardiac silhouette - cant distinguish soft tissue from fluid

Question 4

How is ultrasound used in pleural effusion diagnosis?

Answer 4

• Ultrasound very sensitive at detecting fluid
• Can be done quickly
• Without causing distress to the dyspnoeic patient.
• Can see pleural effusion surrounding the heart

Question 5

How would you diagnose a pleural effusion in a severely dyspnoeic animal?

Answer 5

• Radiographs may stress animal excessively
• Standing ultrasound minimally invasive and rapid; readily detects fluid
• With animal in sternal recumbency, under gentle restraint, receiving oxygen, can do “blind” thoracocentesis (or use ultrasound guidance).

Question 6

List the different fluids that can be found in a pleural effusion

Answer 6

• Transudate
• Modified transudate
• Exudate
• Non-septic
• Septic
• Blood
• Chyle

Question 7

Compare the appearance of a transudate and a modified transudate

Answer 7

Transudate = Clear, watery
Modified transudate = straw coloured; serosanguinous; slightly viscous

Question 8

Which type of pleural effusion is the most common?

Answer 8

Modified transudate

Question 9

Describe a transudate and the possible causes

Answer 9

Low protein, low number of cells
Associated with hypoalbuminaemia

Question 10

Describe a modified transudate and the possible causes

Answer 10

High protein, higher cell numbers than a transudate
- Associated with congestive heart failure, but can be
associated with lung lobe torsion, neoplasia or diaphragmatic rupture

Question 11

How are exudates further classifed?

Answer 11

Blood (haemothorax), chyle (chylothorax), non-septic inflammation (e.g. FIP in cats), or septic inflammation (pyothorax).

Question 12

Describe the protein and cell numbers seen in exudates

Answer 12

High proteins - similar to modified transudates
- More cells than a modified transudate

Question 13

How are pleural effusions treated following thoracocentesis?

Answer 13

• If due to pericardial effusion, need to rapidly carry out pericardiocentesis
• If due to congestive heart failure, treat as CHF
• If due to hypoproteinaemia, investigate and treat the underlying condition

Question 14

What is the most common cause of pericardial effusion in cats?

Answer 14

Congestive heart failure

Question 15

How will the fluid analysis of a non-septic inflammatory exudate appear?

Answer 15

Neutrophils
Macrophages
Mesothelial cells

Question 16

How will the fluid analysis of a septic inflammatory exudate appear?

Answer 16

Degenerate neutrophils
Bacteria
Macrophages
Mesothelial cells

Question 17

How would you treat a pyothorax following thoracocentesis?

Answer 17

• Submit material for culture and sensitivity
• Base antibiotic selection on these results
• Initially, start combination antibiotics to offer broad spectrum
• When stable, insert chest drain(s) (GA).
• Daily thoracic lavage (up to 20mls/kg warmed saline)
• Once lavage fluid is clear, can pull drains.
• Continue A/B for 2-3 months

Question 18

A chylothorax may be associated with what other conditions?

Answer 18

• trauma or mass lesions disrupting thoracic duct / cranial vena cava
• Pericardial disease
• Congestive heart failure
• Lung lobe torsions
• Spontaneous/idiopathic

Question 19

How would you treat a chylothorax following thoracocentesis?

Answer 19

• Treat underlying cause (e.g. CHF)
• Feed low fat diet (high CHO) (reduces chyle prod’n and alters character)
• Add medium chain triglycerides to diet ?
• Rutin (20 – 50 mg/kg q. 8 hours) (may reduce chyle production)
• Almost all cases require surgical management