Pathophysiology of pleural effusions

Question 1

Anatomy of the pleura

Answer 1

• is a serous membrane that covers the lungs
• made up of 2 layers: visceral, parietal
  a) viseral: covers lungs and extends into fissures
  b) parietal: lines inside of the thoracic cavity

Question 2

Pleural space -characteristics/comopsition/function

Answer 2

• 10-20 u thick
• thin layer of fluid
• lubricates movement between the lung and chest wall

Question 3

Visceral pleura -composition

Answer 3

• primarily connective tissue

- covers lung

Question 4

Parietal pleura -composition

Answer 4

• thin layer of loose connective tissue
• contains blood vessels and lymphatic lacunae
• covered by a thin layer of mesothelial cells
• below it is enothoracic fascia

Question 5

Lymphatic stroma - where found

Answer 5

Only within the parietal pleura

Question 6

Lymphatic stroma -function

Answer 6

Remove fluid from the pleural space

Question 7

Visceral pleura -function

Answer 7

Contributes to the elastic recoil of the lung

Question 8

Parietal pleura - function

Answer 8

Fluid is produced and re-absorbed here

Question 9

Normal pleural fluid - volume

Answer 9

• 8 ml per side
• forms at 0.01 ml/kg/hr
• about 15-20 ml per day in 70 kg adult

Question 10

Normal steady state of pleural fluid

Answer 10

-absorption = production

Question 11

Visualization of pleural fluid

Answer 11

• not normally visible on chest x-ray or CT scan

- about 150 ml per side are necessary to see pleural effusion on plain chest x-ray

Question 12

Normal pH of pleural fluid

Answer 12

-about 7.6 normally

Question 13

How does pleural fluid form

Answer 13

• a result of differences in hydrostatic and osmotic pressure between vessels and the pleural space
• parietal pleura is the most important surface for fluid formation + the synthetic vessels that supply pleural surfaces (not from pulmonary circulation)

Question 14

Hydrostatic pressure

Answer 14

• pressure exerted by liquid (i.e. column of fluid) at equilibrium
• in the lungs this reflects the pulmonary venous pressures

Question 15

Oncotic pressure

Answer 15

• osmotic pressure due to proteins and osmoles in the plasma

- draws fluid into the capillaries

Question 16

Balance of oncotic and hydrostatic pressures (contributing to net pressure and gradient in the pleural space)

Answer 16

Flow = change in hydrostatic pressure (parietal pleura vs. visceral pleura) - change in oncotic pressure (parietal pleura vs. visceral pleura)
i.e. the Starling Equation

Because parietal and visceral pleura exterting opposing forces across the pleural space (for both oncotic and hydrostatic)

Question 17

2 main causes of accumulation of pleural fluid in disease states

Answer 17

1. Increased formation

2. Impaired absorption

Question 18

Cause of increased fluid entry

Answer 18

1. Increase in permeability due to disruption of endothelial cell layer (changing K constant -capillary filtration coefficient)
2. Increase in microvascular pressure (i.e CHF)
3. Decreased pleural pressure (ie in atelectasis)
4. Decreased plasma oncotic pressure (ie in nephrotic syndrome, hypoalbuminemia)

Question 19

Other causes of increased fluid entry - from outside the thoracic cavity

Answer 19

• diaphragm permeable excess fluid from other sources can enter the pleura (i.e. communication from other organs)
  a) hepatic hydrothorax
• sucked into chest across diaphragm from abdomen
  b) urinothorax
• abnormal communication from renal collecting system
  c) chylothorax
• abnomal communication with thoracic duct

Question 20

Mechanisms of fluid accumulation due to increase permeability i.e. what is source of increased permeability

Answer 20

• infection
• malignancy
• inflammation

Question 21

Mechanism of pleural fluid accumulation due to shift of starling forces

Answer 21

1) Things which decrease the oncotic gradient
- hypoalbuminemia
2) Things which increase the hydrostatic gradient
- CHF
- Atelectasis

Question 22

Causes of decreased fluid exit

Answer 22

• factors that impair lymphatic drainage

- in many disease states the accumulation of fluid is multi-factorial

Question 23

Common Hx for patient with pleural effusion

Answer 23

• SOB
• pleuritic chest pain
• asymptomatic

Question 24

Physical exam for patient with pleural effusion

Answer 24

• percussion: dullness over area of effusion with decreased tactile fremitus (how does this differ from consolidation in the lung)
• auscultation: decreased air entry

Question 25

Imaging of pleural effusion -modalities

Answer 25

1. Ultrasound
   - close to 100% sensitive for detecting pleural fluid
   - good to identify loculated fluid vs. free-flowing
2. CT contrast
   - especially good for visualizing pleural surface (thickening, tumors, etc)

Question 26

Treatment pleural effusion

Answer 26

Thoracentesis

Question 27

Thoracentesis -how?

Answer 27

1. Insert needle through chest wall into the pleural space
2. Drain pleural fluid
3. Diagnostic and therapeutic
   - can be done with U/S guidance at bedside

Question 28

Analysis of pleural fluid

Answer 28

A) Observation of fluid at bedside
1) Note color
2) Note smell
B) Chemistry (protein, LDH and albumin)
C) WBC count and % differential
D) Cytology (examine for cancer cells)
E) pH and glucose
F) Gram stain and cultures (can include AFB and TB culture if indicated)

Question 29

Classification of pleural effusions

Answer 29

1. Transudates
2. Exuates
   - based on the mechansm of fluid formation and pleural flui chemistry

Question 30

Transudate -general mechanism

Answer 30

-result from an imbalance in oncotic and hydrostatic pressure

Question 31

Exudate - general mechanism

Answer 31

-result of inflammation of the pleura or decreased lymphatic drainage

Question 32

Differentiating transudate vs exudate

Answer 32

Use light’s criteria (analysis of pleural fluid)

• is 85% sensitive for exudate
  a) fluid protein/serum protein > 05
  b) fluid LDH/serum LDH > 0.6
  c) Fluid LDH > 2/3 upper limit of normal

Question 33

Cell count and differential for pleural fluid analysis

Answer 33

> 85% lymphocytes
-TB, cancer, rheumatoid
> 10% eosinophils
-pneumothorax, hemothorax
Neutrophils
-very high in infections

Question 34

Characteristics of trasudate

Answer 34

• low protein and LDH in pleural fluid
• implies intact endothelial membrane
• fluid accumulation from increased hydrostatic pressure or decreased oncotic pressure

Question 35

Characteristics of exudate

Answer 35

• high protein and LDH in pleural fluid

- implies disruption of endothelial membrane

Question 36

Differential diagnosis Transudate

Answer 36

LUCKI ME
L-liver (hepatic hydrothorax)
U - urinothorax
C- CHF
K- Kidney (low protein state - nephrotic)
I - iatrogenic
M-myxedema
E -embolic

Question 37

Exudate

Answer 37

-pretty much everything else (including malignancy, infection, PE, serositis due to connective tissue disease etc)

Question 38

Approach to managing plural effusion

Answer 38

1. Look for underlying cause
2. Thoracentesis for fluid analysis
3. Transudate
   - work up for differential diagnosis (i.e. CHF, urinalysis, urea, creatinine, liver function, TSH, etc)
4. Exudate
   - evaluate for clues to underlying cause
   a) infection
   b) malignant
   c) pulmonary embolism

Question 39

Why would check albumin in pleural effusion

Answer 39

Check gradient between pleural fluid and serum

-help to confirm transudate

Question 40

Amylase

Answer 40

• not routinely indicated

- order if suspect esophageal rupture into pleural space or pancreatic diseases (rupture of a pseudocyst)