Pathogenesis

Pressure sores are the result of damage to deep tissues, which are susceptible to damage from pressure and shearing forces, and superficial tissues which suffer damage from friction and moisture.

• pressure:
  • over the sacrum, greater trochanter, shoulders, occiput and heels
  • deeper tissues are pressed against bone and experience pressures as much as five times greater than the superficial tissues
  • ischaemia occurs where the capillary pressures are exceeded for a long while (pressures of 12 to 32 mmHg)
    
    
• shearing forces:
  • impair tissue circulation, and stretch and angulate deep tissues
    
    
• friction:
  • can cause intraepithelial blistering and superficial erosions
  • damage is accelerated if the skin is wet

Initially the tissues of the hypodermis become necrotic followed by the overlying skin. The skin eventually sloughs off leaving a base of necrotic subcutaneous tissue and fat on granulation tissue. Extensive and prolonged pressure may result in ulceration extending to tendons and bone.