SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 003
1.What
are the main causes of pulmonary edema?
Pulmonary edema is caused by accumulation of fluid within the
pulmonary interstitium and alveoli. The commonest cause is left-sided heart
failure producing increased pulmonary capillary hydrostatic pressure. Increased
vascular permeability due to ARDS, infections, toxins, or sepsis also causes
edema.
Reduced plasma oncotic pressure occurs in nephrotic syndrome,
liver disease, and severe malnutrition. Lymphatic obstruction impairs removal
of interstitial fluid. Excess intravenous fluid administration may produce
fluid overload. High-altitude pulmonary edema occurs in susceptible
individuals.
Neurogenic pulmonary edema follows severe brain injury.
Certain drugs and inhaled toxins may damage alveolar capillaries. All these
mechanisms interfere with normal pulmonary gas exchange.
2.What are the pathologic features of pulmonary congestion
and edema?
Pulmonary congestion is characterized by engorgement of
pulmonary capillaries due to increased venous pressure. The lungs become heavy,
wet, and dark red. Interstitial edema develops first, followed by accumulation
of protein-rich fluid within alveolar spaces. Microscopy shows dilated
capillaries and edema fluid filling alveoli. Long-standing congestion causes
rupture of capillaries with leakage of red blood cells.
Alveolar macrophages ingest hemosiderin and become heart
failure cells. Interstitial fibrosis develops in chronic pulmonary congestion.
Gas exchange becomes progressively impaired. Patients develop
dyspnea, hypoxemia, and reduced lung compliance. Severe pulmonary edema is a
life-threatening medical emergency.
PROFESSOR OF MEDICINE
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