Maintaining skin integrity is a fundamental safety concern in healthcare. Skin breakdown leads to pain, prolonged recovery times, and increased infection risk. Shearing is a major mechanical force that compromises this integrity, especially for individuals with limited mobility. This force causes serious underlying tissue damage that is often not visible until the injury has progressed. Understanding the mechanism of shearing is foundational to effective patient care strategies.
Understanding Shearing and Friction
Shearing and friction are distinct mechanical forces that often occur together. Shearing is an internal force exerted parallel to the body’s surface, acting deep within the tissue layers. It occurs when the outer skin layer is held stationary by friction against a surface, such as a bed sheet, while the skeletal structure and deeper tissues move in a different direction, typically due to gravity.
This opposing movement causes tissue layers to stretch and slide over one another, resulting in deformation and strain. This strain stretches and tears tiny blood vessels anchored to the bone. This vascular damage reduces blood flow and oxygen supply, leading to cell death and deep tissue injury. Shearing is often described as a “bottom-up” injury that progresses outward.
Friction, conversely, is the resistance caused by the skin surface rubbing against an external object. This force primarily affects the superficial layer of the skin (the epidermis) and results in abrasions, similar to a rug burn. Friction is considered a “top-down” injury, making the skin vulnerable to infection. While friction causes superficial damage, its presence is necessary to anchor the skin and allow destructive shearing forces to occur.
How Patient Movement Leads to Shearing
Shearing forces are commonly generated during routine patient positioning and movement, especially when proper techniques are not employed. A primary cause is when a patient slides down in bed after the head of the bed (HOB) has been elevated. When the HOB is raised above 30 degrees, gravity pulls the body mass downward. The skin over the sacrum or coccyx remains fixed to the mattress by friction, while the skeleton moves, creating the destructive internal shear force.
Improper transfer techniques, such as dragging a patient across a bed or chair surface, are another source of shear. The skin is pulled against the bedding while the underlying bony prominences move in the opposite direction. This action generates a significant force that can easily exceed the tissue’s tolerance threshold for injury.
Even small shifts in position, like leaning forward in a wheelchair or chair, can substantially increase shear forces. Localized shear can also occur when a patient attempts to reposition themselves by pushing with their heels or elbows. Therefore, any movement that causes the skin to remain fixed while the underlying bone structure moves must be managed carefully to avoid tissue damage.
Key Nursing Interventions to Prevent Shearing
Preventing shearing requires a proactive and consistent approach focused on minimizing the opposing movement between the skin and the bone. A fundamental intervention is managing the angle of the head of the bed (HOB). Nurses should keep the HOB elevated at 30 degrees or less when the patient is resting, as this angle significantly reduces the gravitational force that causes sliding. If a higher elevation is temporarily needed, the knee section of the bed should be slightly raised to prevent the patient from migrating toward the foot of the bed.
To eliminate the dragging motion during repositioning, nurses must use friction-reducing aids. Techniques like the mandatory use of slide sheets, draw sheets, or mechanical transfer devices ensure the patient is lifted and moved rather than dragged. These aids allow the entire body unit to move simultaneously, preventing the skin from being anchored while the underlying tissue shifts.
Implementing a structured turning and repositioning schedule is also an important part of prevention. This schedule is typically set for every two hours while a patient is in bed, but it may be more frequent based on individual risk assessment. Consistent repositioning redistributes pressure and shear forces away from vulnerable areas, allowing blood flow to return to compressed tissues.
Specialized pressure-redistributing support surfaces, such as advanced mattresses or cushions, help manage and dissipate shear. These surfaces work by increasing the body’s contact area, which lowers the overall force exerted on any single point. Choosing a surface that offers both pressure redistribution and shear reduction is an important consideration for patients identified as being at high risk for skin injury.