Pulmonary Edema

Pulmonary Edema

Write a short note on pulmonary edema.
Answer:

Acute pulmonary edema is the most important form of local edema as it causes serious functional impairment but has special features.

• It differs from edema elsewhere in that the fluid accumulation is not only in tissue space but also in the pulmonary alveoli.

Pulmonary Edema Etiopathogenesis

Pulmonary edema can result from either the elevation of pulmonary hydrostatic pressure or the increased vascular permeability:

• Elevation in pulmonary hydrostatic pressure: In heart failure, there is an increase in the pressure in pulmonary veins which is transmitted to pulmonary capillaries. This leads to a disturbance in the balance between pulmonary hydrostatic pressure and the plasma oncotic pressure so that excessive fluid moves out of pulmonary capillaries into the interstitium of the lungs. Simultaneously endothelium of the pulmonary capillaries develops fenestrations permitting passage of plasma proteins and fluid into the interstitium. The interstitial fluid collected is cleared by the lymphatics. As the capacity of the lymphatics to drain the fluid is exceeded, the excess fluid starts accumulating in the interstitium, i.e. in the loose tissues around bronchioles, arteries, and lobular septa. Next follows the thickening of the alveolar walls because of the interstitial edema. Up to this stage, no significant impairment of gaseous exchange occurs.
  • However, with a prolonged elevation of hydrostatic pressure and due to the high pressure of interstitial edema, the alveolar lining cells break and the alveolar air spaces are flooded with fluid driving the air out of the alveolus, thus seriously hampering the lung function.
  • Examples of pulmonary edema by this mechanism are seen in left heart failure, mitral stenosis, pulmonary vein obstruction, thyrotoxicosis, cardiac surgery nephritic syndrome, and obstruction to the lymphatic outflow by tumor or inflammation.
• Increased vascular permeability: Vascular endothelium and alveolar epithelial cells get damaged leading to increased vascular permeability. Due to this, there is excessive fluid and plasma proteins leak out in interstitium and
  in alveoli.

Pulmonary edema symptoms

Pulmonary edema Pathology

Grossly

The lungs are heavy, moist, and sub crepitant. The cut surface exudes a frothy fluid.

Cardiogenic vs non-cardiogenic edema

Microscopically

• Alveolar spaces are congested.
• Initially excess fluid collects in interstitial lung spaces in septal walls. Later on, fluid fills the alveolar spaces.
• Edema fluid both in the interstitium and in alveolar spaces appears in eosinophilic, granular, and pink proteinaceous material which is admixed with some RBCs and
  macrophages known as heart failure cells.
• Alveolar edema is seen as brightly eosinophilic pink lines along the alveolar margin known as a hyaline membrane.