Causes of decubitus
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Causes of Decubitus Ulcers (Pressure Sores)
A decubitus ulcer is a localized area of tissue necrosis that develops when soft tissue is compressed between a bony prominence and an external surface. It can develop in as little as 4-6 hours of sustained loading, or even faster in debilitated, malnourished individuals.
Primary Mechanism
When pressure on soft tissue exceeds 32 mmHg, it closes both capillary blood flow and lymphatic flow. This causes:
- Deprivation of oxygen to the tissue
- Accumulation of metabolic waste products
If this persists for more than 2 hours, irreversible tissue damage results. - DiMaio's Forensic Pathology, 3rd Ed.
Major Causative Factors
1. Sustained Pressure (Most Common)
The predominant cause. Pressure over bony prominences in patients with altered consciousness or impaired motor activity prevents normal position changes. The most common sites are:
- Sacrum and coccyx (from lying in bed)
- Greater trochanters (from lying in bed)
- Ischial tuberosities (from sitting)
About 95% of all pressure ulcers develop on the lower body - 65% in the pelvic area and 30% on the legs. - Andrews' Diseases of the Skin
2. Shearing Forces
Sliding of one tissue layer over another stretches and angulates blood vessels, causing injury and thrombosis. This typically occurs when the head of the bed is raised too high and the patient's body slides downward - friction fixes the skin and superficial fascia to the sheets while the deeper fascia slides down. Shearing forces are worse in the elderly due to loss of subcutaneous tissue. - DiMaio's Forensic Pathology, 3rd Ed.
3. Friction
Direct mechanical rubbing of skin against surfaces (sheets, clothing) removes the superficial epithelial layers, breaking down the skin's protective barrier.
4. Moisture
Caused chiefly by urinary and fecal incontinence. Moisture reduces skin resistance to all other damaging factors and increases the risk of decubitus ulcers fivefold. - DiMaio's Forensic Pathology, 3rd Ed.
5. Malnutrition
Leads to muscle atrophy and decreased subcutaneous tissue, reducing the natural padding over bony prominences and making pressure more damaging. - Schwartz's Principles of Surgery, 11th Ed.
6. Obesity
A paradoxical risk factor - large quantities of adipose tissue are poorly vascularized, making the underlying tissue more susceptible to ischemia. - DiMaio's Forensic Pathology, 3rd Ed.
Predisposing / Risk Factors (>100 identified)
| Category | Specific Factors |
|---|---|
| Neurological | Depressed sensory/motor function, altered consciousness, spinal cord injury, stroke |
| Metabolic/Vascular | Diabetes mellitus, peripheral vascular disease, cerebrovascular disease, hypotension |
| Systemic illness | Sepsis, anemia, hypoproteinemia |
| Nutritional | Malnutrition, obesity |
| Incontinence | Urinary and fecal incontinence (moisture) |
| Immobility | Inability to reposition, altered activity levels |
| Mental status | Altered consciousness, dementia, sedation |
Prominent risk factors include diabetes mellitus, peripheral vascular disease, cerebrovascular disease, sepsis, and hypotension. - Andrews' Diseases of the Skin
Staging (for context)
| Stage | Description |
|---|---|
| I | Non-blanching erythema of intact skin |
| II | Partial-thickness loss involving epidermis and/or dermis |
| III | Full-thickness loss into subcutaneous fat (not through fascia) |
| IV | Full-thickness loss with involvement of muscle, bone, tendon, or joint capsule |
Key principle: Pressure ulcer formation is accelerated when pressure + friction + shear forces + moisture act together - none of these factors alone is as damaging as their combination. Prevention centers on redistributing pressure at minimum 2-hour intervals. - Schwartz's Principles of Surgery, 11th Ed.
Definition of decubitus positions, and enumerate various types of decubitus
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