Pressure Sores

Introduction

Pressure sores (also called pressure ulcers or pressure injuries) are areas of localised damage to the skin and underlying tissue caused by sustained pressure, shear or friction, almost always over a bony prominence. They occur in patients whose mobility, sensation or overall condition prevents them from naturally shifting their position to relieve pressure - critically ill patients, those with spinal cord injury, and frail older adults are all at particular risk.¹

Pressure sores are largely preventable, and a very large proportion of NHS spending on wound care goes towards a condition that structured prevention programmes can substantially reduce. This makes prevention, rather than treatment after the fact, the central theme of this topic - and a marker of care quality that is now formally measured across NHS settings.²

Pathophysiology

Skin and subcutaneous tissue depend on capillary blood flow for oxygen and nutrient delivery. When external pressure on the tissue exceeds the capillary closing pressure (normally around 32 mmHg), local blood flow is occluded, causing tissue ischaemia. If this pressure is sustained for long enough - as happens when an immobile patient remains in one position - the ischaemic tissue progresses to necrosis.

Shear forces, generated when the skin is dragged over an underlying surface (for example when a patient slides down in a bed or chair), distort and stretch blood vessels at an angle, further impairing perfusion even at lower absolute pressures. Friction damages the superficial epidermis directly, and moisture (from incontinence or sweating) softens the skin and makes it more vulnerable to both friction and shear. All four - pressure, shear, friction and moisture - interact, which is why prevention strategies address them together rather than pressure alone.

Risk factors

• Immobility - critical illness, sedation, spinal cord injury, post-operative patients, and general frailty in older adults⁶
• Reduced sensation - peripheral neuropathy, spinal cord injury, or reduced consciousness, all of which blunt the normal discomfort that prompts a person to shift position
• Malnutrition and low body weight - impairs tissue resilience and wound healing capacity
• Incontinence and moisture - macerates and weakens the skin
• Vascular disease - reduces the tissue's tolerance of any additional ischaemic insult
• Older age, reflecting a combination of thinner skin, reduced subcutaneous fat over bony prominences, and comorbidity
• Previous pressure sore - a strong predictor of further episodes

Structured risk assessment tools, such as the Waterlow score, combine these factors into a single score used on admission and periodically thereafter to identify patients needing more intensive preventive measures.⁴

Clinical features and staging

Pressure sores occur almost exclusively over bony prominences - the sacrum and heels are the commonest sites, followed by the ischial tuberosities (particularly in seated patients), greater trochanters, elbows and occiput.

Clinical examination

• Regular, systematic skin inspection of all pressure-bearing areas, particularly the sacrum and heels, in any patient identified as at-risk
• Blanching test - press gently on reddened skin; skin that blanches (turns white) and refills is at an earlier, reversible stage than skin that remains persistently red (non-blanching)
• Depth, undermining and tunnelling - assessed once a wound has developed, to stage it accurately and guide dressing choice
• Signs of infection - increasing pain, spreading erythema, malodour, purulent discharge, or systemic signs (fever, tachycardia, confusion)
• Nutritional assessment - weight, appetite, and screening tools (for example MUST), since malnutrition both predisposes to and impairs healing of pressure sores

Differential diagnosis

• Moisture-associated skin damage (incontinence-associated dermatitis) - affects skin folds and perineal skin exposed to urine or faeces, generally more diffuse and following the pattern of moisture exposure rather than being confined to a bony prominence
• Skin tears - traumatic, often in fragile older skin, from friction or shearing injury rather than sustained pressure, and not necessarily over a bony prominence
• Arterial or venous leg ulcers - occur at characteristic lower leg sites rather than over pressure-bearing bony prominences; see Skin Ulcers
• Fungal intertrigo - affects skin folds rather than bony prominences, with associated erythema and satellite lesions

Investigations

Pressure sores are staged clinically. Further investigation is directed at identifying complications or contributing factors rather than confirming the diagnosis.

• Wound swab - only if clinical infection is suspected, since chronic wounds are normally colonised with bacteria and swabbing an uninfected wound adds little
• Blood cultures and inflammatory markers - if systemic infection is suspected
• Imaging (X-ray, MRI) and bone biopsy - if osteomyelitis is suspected in a deep (stage 3-4) sore, particularly one that fails to improve with standard wound care
• Nutritional bloods (albumin, prealbumin, vitamin and mineral levels) - to guide nutritional support in patients with poor healing

Management

Prevention - the SSKIN bundle

A structured approach used across NHS settings to reduce pressure sore incidence.⁵

• S - Surface - appropriate pressure-relieving mattresses and cushions for at-risk patients⁸
• S - Skin inspection - regular, systematic checking of vulnerable areas
• K - Keep moving - repositioning at regular intervals (commonly every 2-4 hours, individualised to risk), and encouraging mobility wherever possible
• I - Incontinence/moisture - prompt management of incontinence and skin protection to reduce moisture-related skin damage
• N - Nutrition/hydration - adequate nutrition to support tissue resilience and wound healing

Treatment of an established pressure sore

• Complete relief of pressure from the affected area - the single most important step, without which no dressing or treatment will allow healing
• Dressing selection matched to the wound - hydrocolloid or film dressings for stage 1-2, and more absorptive dressings (foam, alginate) for exudative stage 3-4 wounds
• Debridement of necrotic tissue or slough, surgical, sharp, enzymatic or autolytic, to allow accurate staging and healing
• Negative pressure wound therapy - can be used for selected deeper wounds to promote granulation
• Treat infection - systemic antibiotics for confirmed clinical infection or osteomyelitis, not for colonisation alone
• Nutritional optimisation, involving dietetic input for malnourished patients
• Surgical reconstruction (flap closure) - considered for severe, non-healing stage 3-4 ulcers, particularly in patients with spinal cord injury

Complications

• Local and spreading infection, including cellulitis
• Osteomyelitis - a significant risk with deep, longstanding stage 3-4 sores, particularly over the sacrum and ischial tuberosities
• Sepsis - a real risk from an infected, deep pressure sore, particularly in already frail patients
• Chronic non-healing wounds and sinus tracts
• Malignant transformation (Marjolin ulcer) - squamous cell carcinoma arising within a chronic, longstanding pressure sore, though uncommon⁷
• Prolonged hospital stay and reduced quality of life, and a recognised association with increased mortality in frail patients with severe pressure sores

Red flags

Prognosis

Stage 1 and 2 pressure sores generally heal well once pressure is relieved and appropriate wound care is provided, often within weeks. Stage 3 and 4 sores take considerably longer, sometimes months, and a proportion never fully heal, particularly in patients with ongoing risk factors (persistent immobility, malnutrition, vascular disease) that cannot be fully reversed.³

The outlook is closely tied to the patient's overall condition rather than the wound in isolation: pressure sores are frequently a marker of significant underlying frailty or critical illness, and their presence - particularly at a higher stage - is associated with worse overall outcomes in hospitalised and long-term care populations. This reinforces why structured prevention, rather than treatment after a sore has developed, remains the central priority in this area of care.