Colour
Colour changes due to ischaemia are best assessed at the extreme periphery i.e. the foot and toes.
The foot may be:
- red and cool:
- redness indicates that oxygenated blood is present in the capillaries
- a severely ischaemic foot may be paradoxically red due to reactive hyperaemia, a physiological attempt to extract the maximum amount of oxygen from the compromised blood flow
- white and cool:
- ischaemic skin is initially pale
- arteriolar vasoconstriction is a normal response to cold, if this is the case peripheral pulses should be present
- dusky purple - early necrosis:
- haemoglobin is deoxygenated in the skin capillaries
- initially the colour will blanch with pressure
- as necrosis progresses the capillary walls break down and blanching ceases
- black - established gangrene
- blood flow has ceased
- the area does not blanch
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