Using Support Surfaces to Manage Tissue Integrity

The Role of Shear Stress and Shear Strain in Pressure Injury Development

ABSTRACT

Although other patient safety indicators have seen a decline, pressure injury (PI) incidence has continued to rise. In this article, the authors discuss the role of shear stress and shear strain in PI development and describe how accurate assessment and management can reduce PI risk. They provide explanations of shear stress, shear strain, friction, and tissue deformation to support a better clinical understanding of how damaging these forces are for soft tissue. Clinicians must carefully assess each patient's risk factors regarding shear forces within the contexts of activity and mobility. The authors also provide a toolbox of mitigation strategies, including support surface selection, selection of materials that contact the individual, management of immobility using positioning techniques, and the use of safe patient handling techniques. With a clear understanding of how shear forces affect PI risk and mitigation strategies, clinicians will more accurately assess PI risk and improve PI prevention care plans, ultimately reducing PI incidence to become more aligned with other patient safety indicators.

Quantitative Measurement of the Pressure and Shear Stress Acting on the Body of a Wheelchair User Using a Wearable Sheet-Type Sensor: A Preliminary Study

To provide a safer sitting environment for wheelchair users, it is important to quantitatively measure the forces acting on the contact surface between the seat and the person in the wheelchair. In addition to the pressure acting on the buttocks, shear forces have received particular attention in recent years; however, measuring shear force is more difficult than measuring pressure. To obtain this measurement, a thin and flexible sensor that can be used in a natural state on a wheelchair is needed. Therefore, we constructed a measurement system using our previously developed wearable sheet-type sensor (0.9 mm thick). In this study, preliminary tests were conducted using human dummies before testing on humans. Sensors were placed in four locations on the humanoid dummy's back and buttocks, and the electric wheelchair was tilted and reclined five times each. The results showed that the sensor output pattern was reproducible and valid enough to proceed to the next step. However, the shear force in the internal and external directions was greater than expected, which indicates that the equipment and testing methods must be reviewed. On the basis of the results obtained in this preliminary study, preparations will be made for testing on human subjects.

The relationship between torso inclination and the shearing force of the buttocks while seated in a wheelchair: Preliminary research in non-disabled individuals

The shearing force acting upon the contacting surface of the buttocks while seated in a wheelchair has been linked to the development of pressure ulcers. However, the actual causative factors have not been examined in detail. In an attempt to clarify the nature of this problem, we developed a specific measurement system. In preparation for future clinical applications, we conducted preliminary testing in non-disabled individuals. As a result, we were able to discover a number of issues related to this system and our measurement methods. Although we only evaluated a limited number of typical sitting postures, we were able to record the buttocks shearing force reference values for non-disabled individuals. Our results suggest that regardless of posture, a backward-directed shearing force occurs below the ischial tuberosity in non-disabled individuals in seated positions. This force seemed to increase as the individual leaned forward. Meanwhile, tilting the torso to one side seemed to be associated with an increase in the shearing force working in the opposite direction. We hope that these findings can be utilized for reference purposes in future research among non-disabled individuals.

Choosing a support surface for pressure injury prevention and treatment

This article discusses an evidence- and consensus-based support-surface algorithm designed to help clinicians choose the most appropriate support surface for preventing or treating pressure injuries based on patient, nurse, and institutional considerations.

Influence of polyester spacer fabric, cotton, chloroprene rubber, and silicone on microclimatic and morphologic physiologic skin parameters in vivo

BACKGROUND

Skin diseases can develop upon disadvantageous microclimate in relation to skin contact with textiles of supporting devices. Increased temperature, moisture, mechanical fracture, pressure, and inflammatory processes often occur mutually and enhance each other in their adverse effects. Therefore, the early prevention of skin irritations by improvement of microclimatic properties of skin in contact with supporting devices is important.

MATERIALS AND METHODS

In this study, the microclimate under occlusion with polyester, cotton, chloroprene rubber, and silicone textiles, used for supporting devices, was analyzed by determining several characteristic physiologic skin parameters in vivo, including temperature, moisture, and transepidermal water loss (TEWL). This is achieved by comparing a miniaturized in vivo detection device with several established optical and sensory methods in vivo.

RESULTS

A highly significant TEWL decrease was found after polyester, chloroprene rubber, and silicone application. The application of all materials showed highly significant decrease in skin surface temperature, with chloroprene rubber showing the lowest. Similarly, all materials showed highly significant increase in relative moisture, where the highest increase was found for chloroprene rubber and silicone and the lowest increase for cotton. The cutaneous carotenoid concentration of chloroprene rubber, silicone, and polyester decreased. A manipulation of the surface structure of the stratum corneum was recognized for all materials except for cotton by laser scanning microscopy.

CONCLUSION

The skin parameters temperature, relative moisture, antioxidant status, and TEWL can effectively characterize the microclimatic environment during occlusion with medical supporting materials. These parameters could potentially be used to develop standardized testing procedures for material evaluation.

Preventive Effect of a Microclimate-Regulating System on Pressure Ulcer Development: A Prospective, Randomized Controlled Trial in Dutch Nursing Homes

OBJECTIVE

Prevention of pressure ulcers (PrUs) is based on relieving pressure, diminishing shear stress, and controlling the skin's microclimate. Based on the recommendations in the most recent guideline for prevention of PrUs, a pressure-relieving, shear stress-diminishing, and microclimate-controlling skin interface multilayer support system (Bedcare; Sense Textile, 's-Hertogenbosch, the Netherlands) has been developed for use on top of a viscoelastic foam mattress (Formafoam, Kabelfabriek Eupen, Belgium). The aim of this study was to test the PrU preventive effect of this system compared with a viscoelastic foam mattress alone.

METHODS

A multicenter, prospective, randomized controlled trial was executed in 21 nursing homes in the Netherlands. Residents with a Braden score less than 16, a life expectancy of more than 3 months, and no PrUs during the last 3 months were asked to participate and included after informed consent. Residents were divided into 2 groups. The control group received a new high-quality viscoelastic foam mattress covered with a cotton sheet. The intervention group received the same new mattress, in combination with the newly developed multilayer system. Research nurses followed the participating residents for 12 weeks. The outcome parameter was the development of PrUs.

RESULTS

Two hundred six residents participated in the study. Both groups had comparable demographics (eg, age, Braden score, care dependency, incontinence). In the control group, 5% of the residents developed a category 2, 3, or 4 PrU, and 9% in the intervention group did. These results were not statistically significant.

CONCLUSIONS

This study shows that the multilayer system (Mini Overlay System, barrier mattress cover, and Stay and Transfer Sheet), when used as an integral system and in combination with a viscoelastic foam mattress, has no added value over the viscoelastic foam mattress/cotton sheet.

The Effect of a Liner on the Dispersion of Sacral Interface Pressures During Spinal Immobilization

Sacral pressure ulcers are a significant problem following spinal cord injury and are felt to be in part due to the high interface-pressures generated while strapped to the spine board. The objective of this study was to determine sacral interface-pressure and sensing area in healthy volunteers on a spine board and the effects of a gel pressure dispersion liner. Thirty-seven volunteers were placed on a pressure-sensing mat between the subject and the spine board. Measurements were carried out with and without a gel liner. Pressures and sensing area were recorded every minute for 40 minutes. The highest pressure was generated at the sacral prominence of each subject. Mean interface-pressures were higher on the spine board alone than with the gel liner (p < .0001). Overall, mean sensing area was lower on the spine board than with the gel liner (p < .0001). Standard spinal immobilization causes high sacral interface-pressures. The addition of a gel liner on the spine board decreased overall mean sacral pressures and increased mean sensing area. Generation of sacral pressure ulcers may be related to the initial interface-pressures generated while the patient is strapped to the spine board. The addition of a gel liner may reduce the incidence of sacral pressure ulcers.

The effect of seat shape on the risk of pressure ulcers using discomfort and interface pressure measurements

BACKGROUND

It is clinically known that shape is important when selecting or designing a wheelchair support surface for the prevention of pressure ulcers (a £ 2 billion annual cost to the National Health Service, UK); however, the effect of different levels of shape contouring has not been adequately studied.

OBJECTIVES

To investigate the effect of seat shape on the risk of pressure ulcers using discomfort and interface pressure measurements.

STUDY DESIGN

Randomised, repeated trial.

METHODS

Thirty able-bodied participants sat with restricted movement for 30 min in three sessions to evaluate two cushion shapes against a flat baseline surface. Visual Analog Scaling and pressure mapping were used to measure surrogates for pressure ulcer risk, discomfort and interface pressures, respectively.

RESULTS

Linear regression revealed a reduction in discomfort (p < 0.05) on the custom contoured shapes. Interface pressures measured were also lower (p < 0.05) on the custom contoured shapes, and a negative Pearson's correlation (p < 0.05) indicated an association between smaller hip widths and increased discomfort for the commercially shaped cushion.

CONCLUSIONS

The results of this study confirm that custom contoured shapes were effective at reducing pressure ulcer surrogate measures in the participants of this study and therefore suggests that the contribution of a cushion's three-dimensional contours on pressure ulcer risk should be further researched.

CLINICAL RELEVANCE

The measurement of seat shape, discomfort and interface pressure in surrogate participants can help inform the design of wheelchair seating for individuals who are insensate or otherwise at risk of developing pressure ulcers. This knowledge can now be implemented using modern three-dimensional shape acquisition, analysis and fabrication technologies.

Wheelchair evaluation for the older adult

This article focuses on basic principles of seating and wheelchair evaluation for the general population. The discussion includes wheelchair options, components, and accessories. Basic principles to guide the clinician in the process of selection for maximum function are addressed.