A pressure injury, often called a pressure ulcer or bedsore, is localized damage to the skin and the underlying soft tissue, typically occurring over a bony prominence or a medical device. This damage results from prolonged pressure, or pressure combined with forces like shear and friction. Pressure injuries are a serious and prevalent concern in healthcare, affecting millions annually. Understanding the multiple factors that place an individual at risk is the first step in preventing this painful and potentially deadly complication.
Physical Stressors and Restricted Movement
The primary external cause of a pressure injury is sustained mechanical force concentrated on a small area of the body. Immobility is the root cause that allows these forces to act uninterrupted, preventing the natural shifting of weight that maintains blood flow. When a patient cannot move themselves, the body’s weight continuously compresses the tissue between a bony prominence, such as the sacrum or heel, and an external surface like a mattress.
This unrelieved pressure exceeds the normal pressure inside the capillaries, leading to microcirculatory occlusion and ischemia, which is a lack of blood flow and oxygen. Tissue ischemia causes a buildup of toxic metabolites and ultimately results in cell death and tissue necrosis. Even a short period of immobility, such as two hours, can initiate the process of tissue damage in susceptible individuals.
Beyond direct compression, two other mechanical forces contribute significantly to injury: shear and friction. Shear occurs when the skin remains stationary on a surface while the underlying tissue and bone shift in a parallel, opposing direction, such as when a person slides down in bed. This action stretches and tears blood vessels, which impedes blood flow and can damage deeper tissue structures. Friction is the rubbing of the skin against a rough surface, which can cause superficial damage to the top layer of skin, making the tissue vulnerable to deeper injury.
Localized Factors Affecting Skin Health
The integrity of the skin’s surface plays a major role in its ability to resist external forces. Excessive moisture is one of the most damaging localized factors, typically originating from incontinence, wound drainage, or perspiration. Skin constantly exposed to moisture becomes softened, a process called maceration, which reduces its tensile strength and makes it fragile.
This fragile, weakened skin is more susceptible to damage from friction and shear forces. Incontinence-associated dermatitis (IAD) occurs when urine or feces irritates the skin, causing the skin’s pH to change and its natural barrier function to be compromised. Individuals with IAD are more likely to develop a pressure injury compared to those who are continent. Changes in skin temperature, such as those caused by fever, can also increase the metabolic needs of the tissue, making it more sensitive to oxygen deprivation from pressure.
Underlying Systemic Conditions
Internal health problems reduce the body’s resilience and its ability to repair tissue damage. One of the most common systemic factors is nutritional deficit, which directly affects the body’s ability to maintain skin integrity and heal wounds. Malnutrition, particularly a lack of protein, interferes with collagen synthesis and the tensile strength of the skin, making it easier to break down.
Inadequate hydration is also a significant contributor because water is necessary to support blood flow and cellular metabolism in the tissues. Unplanned weight loss and a low body mass index increase the risk by reducing the natural padding of muscle and fat over bony prominences. This reduction in soft tissue concentrates the pressure directly onto the bone and skin interface.
Impaired circulation, often seen in conditions like diabetes, peripheral vascular disease, or hypotension, prevents oxygen and nutrients from effectively reaching the stressed tissue. When blood flow is already reduced due to disease, the added pressure from immobility quickly leads to tissue death because the cells cannot receive the necessary resources for survival. Patients with sensory perception deficits, such as those with neuropathy or spinal cord injury, are also highly vulnerable. They lack the normal pain and discomfort feedback that would instinctively prompt a person to shift their position, allowing pressure to remain on one area for dangerously long periods.
Assessing and Measuring Patient Vulnerability
Healthcare providers use standardized tools to systematically identify and quantify a patient’s vulnerability to pressure injuries. These assessment scales provide a structured way to evaluate the collective impact of the various risk factors. The Braden Scale is the most widely used tool, evaluating six specific categories:
- Sensory perception
- Moisture
- Activity
- Mobility
- Nutrition
- Friction and shear
Each category is scored numerically, and the scores are summed to yield a total risk level; a lower score indicates a higher risk for injury. Another established tool, the Norton Scale, uses a simpler five-factor assessment covering physical condition, mental condition, activity, mobility, and incontinence. These scales are not meant to replace clinical judgment but serve as a guide to flag patients who require individualized preventative care plans. Regular reassessment is necessary, especially if the patient’s condition changes significantly, to ensure interventions remain appropriate for their current level of risk.