Pathophysiology of Oedema

Study Notes

Oedema is the accumulation of interstitial fluid, causing "pitting oedema" which leaves an indentation after pressure on the affected area.
It results from a disruption of the pressures across the capillaries, leading to fluid movement across the capillary basement membrane.

Pedal oedema: oedema of the lower limbs, resulting from the effect of gravity on venous hydrostatic pressure.
Anasarca: a type of oedema characterized by facial oedema and periorbital puffiness.
Cerebral oedema: oedema affecting the brain.
Macular oedema: oedema affecting the macula of the eye.
Pulmonary oedema: oedema affecting the lungs.

High hydrostatic pressure:
- Congestive heart failure.
- Renal failure.
- Hypervolemic status (e.g. iatrogenic, Conn's syndrome).
- Deep venous thrombosis (DVT) or venous insufficiency.
- Pregnancy.
- Pelvic tumor.
Low plasma oncotic pressure/low serum albumin:
- Nephrotic syndrome.
- Liver failure.
- Malnutrition/malabsorption.
Increased capillary permeability:
- Infection.
- Burn.
- Allergic reaction.
- Trauma.
- Anoxia.
- Acidosis.
Lymphatic obstruction:
- Infection (e.g. filariasis).
- Malignancy.
- Radiation injury.
- Congenital abnormality.

Dependent regions are usually the first site of oedema formation.
Ankle oedema is characteristic, but oedema can also develop over the sacrum in bed-ridden patients.
With increasing severity, oedema will rise higher in the lower limbs and affect the genitalia and abdomen.
Ascites is also common.
Pleural effusion.
Facial oedema and periorbital puffiness are seen in young patients and in cases of low oncotic pressure.

The cause of oedema can be easily detected from the history and physical examination of the CVS and abdomen.
Serum albumin measurement and urine examination for protein are also necessary.

Treatment for specific causes, such as venous thrombosis.
Diuretics with restriction of sodium (sometimes fluids) is rational.
In mild cases, thiazides or small dose loop diuretics (e.g. furosemide) can be used.
In severe cases, large doses of diuretics, sometimes in combination, are required.
In cases of oedema caused by venous or lymphatic obstruction and oedema caused by increased capillary permeability, correction of the underlying cause and local compression (e.g. compressing stockings) are necessary.