2.2 Pressure Injury Staging & Etiology

2.2 Pressure Injury Staging & Etiology

Pressure injuries represent one of the most severe, costly, and debilitating clinical complications encountered in geriatric care. The National Pressure Injury Advisory Panel (NPIAP) defines a pressure injury as localized damage to the skin and underlying soft tissue, usually over a bony prominence or related to a medical or other device. In gerontological nutrition, the Registered Dietitian Nutritionist plays a critical role in evaluating tissue viability, assessing risk, and optimizing metabolic substrates for cellular repair.

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1. Pathophysiology of Pressure Injuries

Pressure injuries develop through a complex cascade of mechanical and cellular disruptions:

1. Pressure and Tissue Deformation: Prolonged pressure and shear deform tissue and impair perfusion. Tissue tolerance depends on duration, anatomy, microclimate, and clinical condition; 32 mmHg is not a universal injury threshold or a safe limit.
2. Shear Forces: Shear occurs when deeper skeletal structures slide downward (such as when a resident slides down in bed while the head of the bed is elevated $>30^\circ$) while the superficial skin and epidermis adhere to bed linens. Shear exerts parallel mechanical traction, angulating, stretching, and tearing perforating microvessels at the fascial boundary. This triggers extensive muscle and subcutaneous necrosis deep within the tissue long before the superficial skin breaks.
3. Friction: Mechanical resistance between the skin and external surfaces strips the protective stratum corneum. While friction alone causes superficial epidermal excoriation, it dramatically compromises skin barrier integrity, accelerating pressure-induced breakdown.
4. Ischemia-Reperfusion Injury: Periodic relief of pressure restores blood flow, but the influx of oxygen triggers a massive burst of reactive oxygen species (ROS), activation of neutrophils, and release of proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1). This paradoxically amplifies microvascular thrombosis, cell membrane damage, and secondary necrosis.

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2. High-Risk Anatomical Bony Prominences

Because pressure is concentrated over focal skeletal contours, specific anatomical sites carry elevated risk depending on posture:

• Supine Position: Sacrum, coccyx, calcaneus (heels), occiput, and scapular spines. The calcaneus is especially vulnerable due to minimal subcutaneous fat cushioning and poor collateral perfusion.
• Seated / Wheelchair Position: Ischial tuberosities bear the highest localized sitting pressures (often exceeding $100\text{ mmHg}$), alongside the sacrum, coccyx, spinous processes, and heels.
• Lateral (Side-Lying) Position: Greater trochanters of the femur, lateral and medial malleoli, lateral condyles of the knee, acromion processes, and the ears.
• Medical Device-Related Sites: Nasal bridge and cheeks (CPAP/BiPAP masks), posterior ears (oxygen nasal cannulas), lips and tongue (endotracheal tubes), urethral meatus (indwelling catheters), and wrists/ankles (protective restraints).

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3. NPIAP Staging Criteria

The NPIAP staging system classifies tissue damage based on the deepest anatomical layer of visible or palpable tissue destruction:

Special Clinical Rule: The Intact Ischemic Heel Eschar

Stable, intact, dry, adherent eschar without erythema, fluctuance, or purulence on an ischemic limb or heel serves as a protective cover. Do not moisten, soften, or surgically debride stable dry heel eschar. Debridement opens a non-vascularized portal for invasive bacterial infection and gangrene.

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4. Differential Diagnosis: Pressure Injury vs. MASD / IAD

Misclassifying Incontinence-Associated Dermatitis (IAD) as a pressure injury is a common clinical and regulatory error in long-term care:

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5. Validated Risk Assessment Tools

Standardized screening enables proactive nutritional and nursing intervention before skin breakdown occurs:

The Braden Scale for Predicting Pressure Sore Risk

The Braden Scale is the most widely validated risk assessment instrument in geriatric facilities. It evaluates six clinical subscales:

1. Sensory Perception (1--4): Ability to respond meaningfully to pressure-related discomfort.
2. Moisture (1--4): Degree to which skin is exposed to moisture (perspiration, urine).
3. Activity (1--4): Degree of physical activity (bedfast, chairfast, walks occasionally, walks frequently).
4. Mobility (1--4): Ability to change and control body position.
5. Nutrition (1--4): Usual food intake pattern (1 = Very Poor [$<1/3$ meal], 2 = Probably Inadequate [$1/2$ meal], 3 = Adequate [$>1/2$ meal], 4 = Excellent).
6. Friction and Shear (1--3): Problem, potential problem, or no apparent problem during transfers and positioning.

$\text{Braden Total Score Range: } 6 \text{ to } 23$

• Score $\le 9$: Very High Risk
• Score $10\text{--}12$: High Risk
• Score $13\text{--}14$: Moderate Risk
• Score $15\text{--}18$: Mild / At-Risk
• Score $19\text{--}23$: No Current Risk

Clinical Assessment: A low Braden total or nutrition subscore warrants assessment and an individualized prevention plan. Provide nutrition replacement when indicated, appropriate pressure redistribution, and a nursing repositioning schedule based on tolerance and needs; the score alone does not require every micronutrient to be supplemented.

The Norton Scale

Evaluates five parameters: Physical Condition, Mental Condition, Activity, Mobility, and Incontinence, each scored 1 to 4 (total range 5 to 20). A score of $\le 14$ denotes significant pressure injury vulnerability.

Medical-device-related pressure injuries of skin use the staging system. Mucosal pressure injuries are not staged because mucosal anatomy does not permit the same tissue-depth categories. Do not reverse-stage a healing injury; document its original stage and current healing findings.

Primary source check

NPIAP staging clarifications, checked October 13, 2026.