by mtoom


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What is the pleura? How many layers does it have?
Pleura: Serous membrane that covers the lungs

2 layers:
  • Visceral: Covers lungs, extends into fissures
  • Parietal: Lines inside of thoracic cavity 
How thick is the pleura? What lies in the pleural space?
  • 10-20 μm thick
  • Thin layer of fluid in the space, to lubricate movement between the lung and chest wall
What is an important histological difference between the visceral and parietal pleura?
  • Visceral pleura: Connective tissue covering the lung
     
  • Parietal pleura: Thin layer of loose connective tissue, containing blood vessels and lymphatics. Covered by a thin layer of mesothelial cells
What are and where are the lymphatic stoma? What do they do?
  • The lymphatic stoma are basically holes into the lymphatic system (found in the walls of the parietal pleura)
     
  • They remove fluid from the pleural space
What is one of the core functions of the visceral pleura (in terms of its connective tissue)?
Contributes to elastic recoil of the lung
Where is the fluid in pleural space produced and reabsorbed?
The fluid is both produced and reabsorbed in the parietal pleura.
  • How much pleural fluid is on each side of the lung?
  • Can can be said about absorption/reabsorption?
  • Is the fluid visible on CT/x-ray?
  • 8 ml
  • Fluid is in steady state (Rate of production = rate of absorption)
  • Fluid not normally visible on X-ray (>150ml per side necessary to see pleural effusion)
Describe the basic physiology behind formation of the pleural fluid
Occurs as a result of differences in hydrostatic and osmotic pressure between vessels and pleural space
The pleura is supplied by blood vessels from where?
Systemic system (not pulmonary circulation)
The hydrostatic pressure in the lungs reflects what?
Pulmonary venous pressure
What law/equation governs the regulation of pleural fluid in the pleural space?
Starlings equation
Name 4 vascular mechanisms that can lead to ↑ fluid entry.
  • permeability in vessels
  • microvascular pressure (e.g. CHF) increases hydrostatic gradient
  • pleural pressure (e.g. atelectasis)
  • plasma oncotic pressure (e.g. nephrotic syndrome, hypoalbuminemia) decreases oncotic gradient
Describe 4 ways that fluid can leak from other organs into the pleural cavity.
  • Hepatic hydrothorax: Ascites fluid from cirrhosis leaks through diaphragm into pleural space.
  • Urinothorax: Abnormal communication from renal collecting system
  • Chylothorax: Abnormal communication with thoracic duct
  • Other sources: CSF, esophagus, pancreas
Describe 3 conditions resulting in ↑vessel permeability that can lead to pleural effusion.
  • Infection
  • Malignancy
  • Inflammation
Besides increased fluid entry into the pleural cavity, what else may cause effusion? How?
Decreased fluid exit
  • Impaired lymphatic drainage leads to a decreased absorption of fluid 
  • Fluid accumulation is often multifactorial
What are possible history findings (3) and physical exam findings (2) in a pleural effusion?

History
  • SOB
  • Pleuritic chest pain
  • Asymptomatic

Physical exam
  • Dullness on percussion
  • Decreased air entry 
What is the imaging modality of choice to diagnose pleural effusion?

Name 2 other options
Ultrasound
  • ~100% sensitivity for pleural fluid
  • Typically used instead of a decubitus film 

Other options
  • X-ray (decubitus film)
  • CT w/ contrast 
What is thoracentesis? What is it used for (2)?
Thoracentesis: Inserting a needle through chest wall into pleural space

Done to either: diagnose effusion, drain pleural fluid.

Often done with ultrasound guidance
Describe 4 colours (of pleural fluid) you might see and what they mean
  • White: pus/chylothorax
  • Frank blood: hemothorax
  • Bloody: serum & blood
  • Straw-coloured: serum
What are 2 causes of foul-smelling pleural fluid?
  • Infection
  • Urine
What analysis is done on pleural fluid? (6)
  • Chemistry (protein, LDH, albumin)
  • WBC count and differential
  • Cytology (examine for cancer cells)
  • pH
  • Glucose
  • Gram stain/cultures (e.g. AFB)
What is transudate vs exudate? Which has both ↑Protein and ↑LDH?
Transudate
  • Intact endothelial membrane
  • Fluid accumulates due to ↑hydrostatic pressure or ↓oncotic pressure
  • ↓[Protein] and ↓[LDH] concentrations in fluid
Exudate
  • Disruption of endothelial membrane
  • Local process
  • ↑[Protein] and ↑[LDH] in fluid
What is Light's Criteria?

Light's Criteria for Exudate, if at least one of the following is true:
  • Fluid protein / serum protein > 0.5
  • Fluid LDH / serum LDH > 0.6
  • Fluid LDH > 2/3 upper limit of normal

Otherwise, assume Transudate
Describe Transudate pneumonic (7)
LUCKIME
  • L: Liver
  • U: Urinothorax
  • C: CHF
  • K: Kidney
  • I: Iatrogenic
  • M: Myxedema
  • E: Embolic
Name 3 causes of Exudate
  • Malignancy
  • Infection
  • Pulmonary embolism
Name 5 common causes of pleural effusions
  • CHF
  • Pneumonia
  • Cancer
  • PE
  • Cirrhosis
What is the approach to pleural effusion (3)?
  • 1. Look for underlying cause and treat (e.g. patient in obvious CHF)
  • 2. Thoracentesis for fluid analysis

    If Transudate: LUCKIME
    -Do work-up for differential diagnosis

    If Exudate:
    -Evaluate for: Infection, malignancy (asbestos exposure), PE
Name 4 other special tests sometimes done on pleural fluid
  • Albumin: Confirm fluid is a transudate, by comparing [albumin] in fluid with [albumin] in serum
  • Amylase: If suspected esophageal rupture into pleural space
  • Triglycerides/Chylomicrons: Confirm a chlyothorax
  • Creatinine: Confirm a urinothorax
What is a parapneumonic effusion?
When a pneumonia leads to secondary infection of the pleural fluid
What are the 3 types of Parapneumonic effusions? Describe them.
  • Uncomplicated effusion: Meets Light's Criteria for exudate (as you'd expect for an effusion caused by infection)
  • Complicated effusion: pH less than 7.2
  • Empyema: Frank pus, positive gram stain, positive culture
When do you use a chest tube to drain pleural fluid? (2)
  • Complicated (low pH)
  • Empyema

If drainage insufficient, surgical decortication may be required.
What can empyema lead to?
Severe sepsis
What are the 2 general types of causes of a malignant effusion?
  • Primary (mesothelioma)
  • Metastatic (more common)
    -Lung
    -Breast
    -Lymphoma
    -GI/GU
    -Ovarian 
Describe 2 routes ways that a malignancy will cause a pleural effusion?
Direct (cancer physically causes the effusion)
  • Hematogenous spread to the pleura
  • Obstruction of pleural lymphatics
Indirect (secondary effect of cancer leads to effusion)
  • Hypoproteinemia
  • Post-obstructive pneumonitis
  • Treatment-related
  • PE
  • Thoracic duct obstruction
  • Pericardial involvement
What percentage of patients with a pulmonary embolism have a pulmonary effusion as a result? What is the mechanism?
  • 30-50% with embolism have effusion as well
  • Mechanism: ↑right heart pressure → ↑pulmonary capillary permeability
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