Edema is the collection of fluid in the interstitial spaces or serous cavities. It becomes evident only when 5-6 liters of fluid has accumulated in the water depots.
Pitting on pressure occurs when the circumference of the limb is increased by 10%.
Mechanism : One or more of the following factors may be responsible.
- Increased capillary permeability when it is damaged e.g. acute inflammation.
- Increased capillary pressure e.g. cardiac failure.
- Decreased osmotic pressure of the blood e.g. hypoproteinemia.
- Damaged lymphatic drainage e.g. filariasis.
Site
Venous edema commonly occurs in the lower limbs which are most dependent. However, if the patient is recumbent (i.e. lies on his back), edema may be present only over the sacral region which is, then, most dependent. Lymphatic edema may occur in either limbs or over scrotum depending upon the site of involvement.
Causes
Bilateral Edema:
- Cardiac: CCF, LVF, pericarditis
- Renal: Acute nephritis, nephrosis
- Hepatic: Cirrhosis of liver, portal hypertension
- Venous: Inferior vena cava obstruction
- Endocrine: Myxedema
- Allergic: Angionurotic edema
- Nutritional: Anemia, hypoproteinemia, beriberi.
- Toxic: Epidemic dropsy
Unilateral:
A. Lymphatic:
- Filarial
- Pressure by new growth, metastasis
- Radiation
B. Traumatic: Bruises, sprains, fractures
C. Infections: Cellulitis, boils, carbuncle
D. Metabolic: Gout
E. Venous: Venous thrombosis, varicose vains.
F. Hereditary: Milroy’s disease
