Expansion
Raised hydrostatic pressure, low oncotic pressure, increased permeability, lymphatic obstruction
Expansion
| Mechanism | Examples |
|---|---|
| Raised capillary hydrostatic pressure | Heart failure, venous obstruction, fluid overload, pregnancy |
| Reduced plasma oncotic pressure | Nephrotic syndrome, liver failure, malnutrition, protein-losing enteropathy |
| Increased capillary permeability | Sepsis, burns, anaphylaxis, inflammation |
| Lymphatic obstruction | Filariasis, malignant infiltration, post-surgical or post-radiotherapy lymphoedema |
Two clinical distinctions follow from the mechanism. Oedema from raised hydrostatic pressure or low oncotic pressure is protein-poor and pits; lymphoedema and inflammatory oedema are protein-rich and are typically non-pitting, with skin thickening over time.
And distribution helps: cardiac oedema is dependent, gravity-determined and symmetrical; hypoalbuminaemic oedema is generalised and often periorbital; venous or lymphatic obstruction is unilateral.