by Aubrey Knick-Koppenhofer, PT, DPT, NCS, and Janelle Carnahan, PT, DPT, ATP
Acquired pressure injuries are a significant health problem that can be painful for clients and costly to treat. Fortunately, these injuries are often avoidable. To prevent these injuries, a risk assessment should be performed to identify at-risk clients and develop individualized preventative interventions.1 Risk assessment tools, including pressure mapping, can be useful but should not be solely relied upon for prevention, and other risk factors should be considered.
When identifying those at risk of developing pressure injuries, the clinician should consider the following risk factors: existing pressure injuries, sensation, mobility limitations, increased skin moisture, increased body temperature, impaired circulation, poor nutritional status, postural/orthopedic deformities, exposure to friction or shear forces, medical conditions, and general health status. In addition, the clinician should consider the client’s daily activities, including the client’s use of medical equipment, to assess the risk of pressure and shear forces. The clinician should also visually inspect the skin and pay special attention to bony prominences, skin folds, and where skin is in contact with medical devices.1 Typically, pressure injuries first develop at the underlying tissue and may not show visible skin damage in the early stages. Pressure mapping technology can aid the clinician in assessing pressure distribution and areas of potential tissue damage.
Pressure mapping technology consists of a computer with pressure mapping software, a flexible sensor pad, and an electronics unit. There are four main types of pressure mapping measurements: single sensor, single measurement; multiple sensor, single measurement; single sensor, continuous measurement; and multiple sensor, continuous measurement. The most common clinically used system is a multiple sensor pad placed between a support surface and the client, which displays a digital reading of pressure information on a computer screen. The colors and numbers on the screen correspond to pressure readings expressed as millimeters of mercury (mmHg). Generally, areas of higher pressures are shown in red, and areas of lower pressures are shown in blue. The pressure readings are useful in assessing pressure distribution and areas of peak pressure. Continuous measurements of the pressure readings can provide information on how postural and seating adjustments impact the pressure distribution. The client can also see how his or her position changes impact the pressure distribution.3,4
Studies have used values of 32 mmHg to 60 mmHg as an acceptable level of pressure based on capillary pressure.? However, pressure measurements made at the skin’s surface are thought to be significantly lower than those at the tissue level, where pressure injuries initially develop. As a result, it is difficult to determine a specific pressure value threshold, rather the overall distribution of pressure, and dispersion index should be considered.2 Additionally, clients with sensation can share information on subjective comfort. Pressure mapping technology can be utilized to select support surfaces including seat cushions, mattresses, bathing/toileting equipment, and travel seats.
Wheelchair seating and positioning is an important part of preventing pressure injuries, as clients typically spend most of the day in a seated position. Using pressure mapping technology and clinical judgment, clinicians help clients to select an appropriate seat cushion. Seat cushion types include foam, fluid foam combination, air filled, off-loading, and custom molded.?
Foam cushions usually have multiple layers of foam with varying densities contoured to provide skin protection and postural support. Fluid foam combination cushions have contoured foam, but also include fluid or air-filled inserts to provide additional pressure relief for the bony prominences of the pelvis. Fluid foam combination cushions typically come with adjustment kits that include foam postural supports and additional fluid packs to assist with positioning and pressure-relieving capabilities. Air-filled cushions have air-filled cells throughout the seat surface that constantly conform to the movements of the client’s body. Off-loading cushions utilize orthotic principles to off-load the boney prominences of the pelvis. Custom molded seating systems use plaster molding, foam in place, or digital technology to customize the seating system to the client. These custom molded systems are often used for clients with rigid postural deformities or to block abnormal movements.
Modifying Existing Seating
Once the clinician selects an appropriate seat cushion for the client, it can take time before the new seat cushion is available to be used by the client for various reasons. As a result, the clinician may need to make modifications to a client’s existing seating system. As noted earlier, pressure mapping technology can provide continuous measurements of pressure readings, so the clinician can see the effects on pressure distribution while changing the seated position of the client. For example, if the client presents with a flexible posterior pelvic tilt, the clinician may add a lumbar support to maintain a neutral pelvis. Or if the pelvis is fixed, the clinician may change the seat to back angle to help improve the client’s upright seated posture. To accommodate or adjust for pelvic obliquities, the clinician may use obliquity build-ups or wedging. Appropriately positioned and fitted lap belts may also help maintain pelvic alignment. Additionally, the clinician may modify or add lower extremity or trunk supports for improved postural alignment.
For lower extremity supports, adjustments may be made to footplate height or width and the clinician may add abductor or adductor pads and lateral thigh guides to maintain the lower extremities in a neutral position. For trunk supports, the clinician may add thoracic lateral supports to correct flexible deformities such as scoliosis. Air- or gel-filled packs can be added to areas of seat or back cushions to off-load or provide additional pressure relief for high risk areas. New or worsening postural deformities may occur if the seat upholstery is hammocking. In this case, solid seat inserts can be added beneath the seat cushion to provide a stable seat surface.
While the selection of an appropriate seat cushion and optimizing seated posture is critical in preventing pressure injuries, client education is equally important. Key areas of education include: avoiding moisture accumulation, identifying warning signs of pressure injury, weight shifting techniques and frequency, clothing selection, transfer techniques to reduce shearing, nutrition, and minimizing the use of head of bed elevation. To avoid moisture, a few common recommendations are that the client fully dry before dressing, establish a schedule for bladder and bowel management when incontinence is present, and avoid the use of diapers where moisture can be trapped against skin. For weight shifting, a clinician may recommend a change in positioning in the bed every 2 hours and in the chair every 30 minutes.3 While seated in the chair, weight shifting may be performed by anterior or lateral movements that are maintained or utilizing power seat functions. When utilizing power seat functions, a clinician may recommend that the tilt movement should be performed before the seat recline and leg elevation movements to prevent shearing.?
Pressure mapping technology can provide visual feedback to the clinician and client regarding the effectiveness of the weight shifting technique. For clients who are able to perform transfer board or lateral transfers, education and training in body mechanics to achieve off-loading of pelvis as well as performing proper setup are critical in maintaining skin integrity. Proper setup includes moving the client’s body forward past the wheel to prevent contact, performing full scapular depression for clearance, and placing a transfer board fully under the client’s thigh so that it is visible between the thighs prior to transferring.
Clients who are unable to safely and effectively complete these transfers may require the use of a mechanical patient lift. When using such a lift, it is recommended that the clinician remove the sling immediately after the completion of the transfer, as the sling may impact the pressure-relieving ability of the seat cushion. Clients who require the use of a hospital bed with a pressure-relieving mattress may adjust the head of bed angle to accomplish activities of daily living and positioning. However, frequent elevation changes of the bed may cause shearing and should only be performed when necessary. Studies have shown that the head of bed angle should be less than 30 degrees to avoid increased pressure on the sacrum.? If the client requires a head of bed angle of 30 degrees or higher due to medical necessity (ie, tube feeding, respiratory compromise, etc), the client’s lower body should be positioned to minimize pressure on the sacrum.
Clinicians can help prevent and manage pressure injuries by implementing strategies that address the specific risks and needs of the client. Pressure mapping technology is a helpful tool and should be used as part of a comprehensive treatment plan, which emphasizes client education. RM
Aubrey Knick-Koppenhofer, PT, DPT, NCS, is a senior physical therapist at Kessler Institute for Rehabilitation, West Orange, NJ. She has had experience in wheelchair seating and mobility in a variety of neurologic diagnoses, including spinal cord injury, stroke, and brain injury. In 2017, she was awarded the professional designation of board-certified clinical specialist in neurologic physical therapy by the ABPTS of the APTA.
Janelle Carnahan, PT, DPT, ATP, is a clinical specialist physical therapist at Kessler Institute for Rehabilitation in West Orange, NJ. Her main areas of clinical experience have been related to spinal cord injury with special focus on upper extremity management and seating and positioning. For more information, contact RehabEditor@medqor.com.
1. Preventing pressure injuries. The Joint Commission. Issue 25. July 2016. https://www.jointcommission.org/assets/1/23/Quick_Safety_Issue_25_July_20161.PDF
2. Swain I. The measurement of interface pressure. Pressure Ulcer Research. 2005:51-71. Springer Berlin Heidelberg; Heidelberg, Berlin.
3. Crawford SA, Stinson MD, Walsh DM, Porter-Armstrong AP. Impact of sitting time on seat interface pressure and on pressure mapping with multiple sclerosis patients. Arch Phys Med Rehabil. 2005;86(6):1221-1225.
4. DiGiovine C. The dispersion index as a metric for measuring pressure distribution on seat surfaces: a Pilot Study. Presentation at RESNA Annual Conference; June 2015; Denver, Colo.
5. Ferguson-Pell MW. Seat cushion selection. J Rehabil Res Dev Clin Suppl. 1990(2):49-73.
6. Jan Yih-Kuen, Jones MA, Rabadi MH, Foreman RD, Thiessen A. Effect of wheelchair tilt-in-space and recline angles on skin perfusion over the ischial tuberosity in people with spinal cord injury. Arch Phys Med Rehabil. 2010;91(11):1758-64.
7. Peterson M, Schwab W, McCutcheon K, van Oostrom JH, Gravenstein N, Caruso L. Effects of elevating the head of bed on interface pressure in volunteers. Crit Care Med. 2008;36(11):3038-42.