aetiology

Last reviewed 01/2018

Systemic and wound oedema develops after a burn due to a number of factors:

• increased capillary permeability:
• triggered by inflammatory mediators
• increased diffusion, filtration and large molecular transport
• the latter is the most pronounced and there is a great increase in albumin transit
• the basement membrane may remain a selective filter for large molecules despite the disruption of endothelium
• decreased plasma oncotic pressure due to loss of albumin
• increased capillary hydrostatic pressure:
• increased flow to the area due to vasodilatation stimulated by the stress response
• increased resistance to outflow from post-capillary erythrocyte sludging and venular constriction
• decreased tissue hydrostatic pressure due to unfolding of complex macromolecules eg collagen
• increased tissue oncotic pressure due to:
• increased leak of plasma albumin into this space
• breakdown of intercellular ground substance into more osmotically-active units

Overall, the interaction of Starling Forces tend to favour transit of fluid into the interstitial space and hence oedema.