Page 117 - Textbook of Pathology, 6th Edition

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CHAPTER 5

Figure 5.7 Pulmonary oedema. The alveolar capillaries are congested. The alveolar spaces as well as interstitium contain eosinophilic,
granular, homogeneous and pink proteinaceous oedema fluid alongwith some RBCs and inflammatory cells.

pulmonary hydrostatic pressure and the plasma oncotic respiratory ill-effects. Commonly, the deleterious effects
pressure so that excessive fluid moves out of pulmonary begin to appear after an altitude of 2500 metres is reached.
capillaries into the interstitium of the lungs. Simultaneously, These changes include appearance of oedema fluid in the Derangements of Homeostasis and Haemodynamics
the endothelium of the pulmonary capillaries develops lungs, congestion and widespread minute haemorrhages.
fenestrations permitting passage of plasma proteins and fluid These changes can cause death within a few days. The under-
into the interstitium. The interstitial fluid so collected is lying mechanism appears to be anoxic damage to the
cleared by the lymphatics present around the bronchioles, pulmonary vessels. However, if acclimatisation to high
small muscular arteries and veins. As the capacity of the altitude is allowed to take place, the individual develops
lymphatics to drain the fluid is exceeded (about ten-fold polycythaemia, raised pulmonary arterial pressure, increased
increase in fluid), the excess fluid starts accumulating in the pulmonary ventilation and a rise in heart rate and increased
interstitium (interstitial oedema) i.e. in the loose tissues around cardiac output.
bronchioles, arteries and in the lobular septa. Next follows
the thickening of the alveolar walls because of the interstitial MORPHOLOGIC FEATURES. Irrespective of the under-
oedema. Upto this stage, no significant impairment of lying mechanism in the pathogenesis of pulmonary
gaseous exchange occurs. However, prolonged elevation of oedema, the fluid accumulates more in the basal regions
hydrostatic pressure and due to high pressure of interstitial of lungs. The thickened interlobular septa along with their
oedema, the alveolar lining cells break and the alveolar air dilated lymphatics may be seen in chest X-ray as linear
spaces are flooded with fluid (alveolar oedema) driving the air lines perpendicular to the pleura and are known as Kerley’s
out of alveolus, thus seriously hampering the lung function. lines.
Examples of pulmonary oedema by this mechanism are Grossly, the lungs in pulmonary oedema are heavy, moist
seen in left heart failure, mitral stenosis, pulmonary vein and subcrepitant. Cut surface exudes frothy fluid (mixture
obstruction, thyrotoxicosis, cardiac surgery, nephrotic of air and fluid).
syndrome and obstruction to the lymphatic outflow by Microscopically, the alveolar capillaries are congested.
tumour or inflammation. Initially, the excess fluid collects in the interstitial lung
spaces (interstitial oedema). Later, the fluid fills the
2. Increased vascular permeability (Irritant oedema). The alveolar spaces (alveolar oedema). Oedema fluid in the
vascular endothelium as well as the alveolar epithelial cells interstitium as well as the alveolar spaces appears as
(alveolo-capillary membrane) may be damaged causing eosinophilic, granular and pink proteinaceous material,
increased vascular permeability so that excessive fluid and often admixed with some RBCs and macrophages
plasma proteins leak out, initially into the interstitium and (Fig. 5.7). This may be seen as brightly eosinophilic pink
subsequently into the alveoli. lines along the alveolar margin called hyaline membrane.
This mechanism explains pulmonary oedema in examples Long-standing pulmonary oedema is prone to get
such as in fulminant pulmonary and extrapulmonary infected by bacteria producing hypostatic pneumonia
infections, inhalation of toxic substances, aspiration, shock,
radiation injury, hypersensitivity to drugs or antisera, which may be fatal.
uraemia and adult respiratory distress syndrome (ARDS).
Cerebral Oedema
3. Acute high altitude oedema. Individuals climbing to high
altitude suddenly without halts and without waiting for Cerebral oedema or swelling of brain is the most threatening
acclimatisation to set in, suffer from serious circulatory and example of oedema. The mechanism of fluid exchange in the