Mechanism of edema

1. MECHANISM OF OEDEMA

2. Oedema is caused by mechanisms that interfere with normal fluid balance of plasma, interstitial fluid and lymph flow. Movement of fluid- controlled by opposing effects of vascular hydrostatic pressure and colloid osmotic pressure. Exit of fluid from arteriolar end is balanced by inflow at venular end of microcirculation. Small residual amount of excess interstitial fluid is drained by lymphatics .

3. 1 . INCREASED CAPILLARY HYDROSTATIC PRESSURE Rise in hydrostatic pressure at the venular end of capillaries to a level more than plasma oncotic pressure ↓ Minimal/ No reabsorption of fluid at venular end ↓ OEDEMA

4. 2. REDUCED PLASMA OSMOTIC PRESSURE Reduced albumin synthesis in liver / protein malnutrition ↓ Fall in plasma oncotic pressure ↓ Net movement of fluid into interstitial tissues ↓ OEDEMA

5. 3. LYMPHATIC OBSTRUCTION Impaired lymphatic drainage ↓ Localized LYMPHOEDEMA Radical mastectomy for Ca breast Pressure on main lymph ducts Inflammation of lymphatics Occlusion of lymphatics by malignant cells Milroy’s disease

6. 4. SODIUM & WATER RETENTION Hypovolaemia ↙ ↓ ↘ Renal vasoconstiction Renin ↑ADH ↓ ↓ ↓ ↓GFR Aldosterone Reabsoption of water ↓ ↓ ↙ Renal retention of Na & water ↓ OEDEMA

7. 5. INFLAMMATION Capillary endothelial injury by toxins/ histamine/ anoxia/ drugs ↓ Endothelial gap ↓ ↑ Capillary permeability to plasma protiens ↓ ↓Plasma oncotic pressure ↓ OEDEMA

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