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