GRACE UNDER PRESSURE: AN INTRODUCTION TO PRESSURE MAPPING

Marvin Williams, MSBME, Seating Department, Shriners Hospital for Children, Tamp, Florida


Abstract

Computerized pressure mapping systems provides a means of both qualitatively and quantitatively measuring patient sitting pressures. It has the potential to be a tremendous tool for wound prevention, patient and parent/caregiver education, and hospital cost savings. The primary patients monitored at this time are those at risk for skin problems (patients with a previous history of skin breakdown, myelomeningocele, spinal cord injury, etc.). Also monitored are "special cases" such as patients who experience pain in sitting and patients with significant bony prominence which might lead to skin problems (ischial, trocanteric, and/ or coccygial prominece most notably).

Pressure mapping can be beneficial to would management and prevention by giving the clinical team a qualitative measure of a patient's sitting pressures. If the pressures are deemed to high, the patient's seating can be adjusted accordingly to reduce the pressures to a more acceptable range. By possibly preventing a wound from occurring or worsening, the system shows promise as a cost savings tool for hospitals and wound centers.

The system can also be used as a tool for patient and parent/caregiver education. It allows them to see exactly why a specific seat cushion is necessary or why they feel pain when sitting in some instances. The pressure mapping system provides a graphical representation for a greater qualitative analysis and understanding of what is occurring with the sitting patient.

Introduction

Studies on pressure ulcers and patient-surface interface pressures have been ongoing of over 50 years with varied results. Due to technological advances over the past 15 years, namely the use of computers and digital sensing technology, some of the most beneficial and exciting work has come about. The development of pressure mapping technology is proving itself to be a useful new tool to the seating and clinical wound treatment team.

Pressure mapping is both a qualitative and quantitative means of assessing the interface pressure between a patient and a given surface. In this case, the given surface is a seat cushion. Pressure mapping is qualitative in that it gives the clinician a visual representation of the interface pressures. It is quantitative in that the system also gives the clinician actual numerical interface pressures values. While the absolute meaning of the numerical data is still open to debate (1, 4, 8 ), it does provide a relative means of in-depth analysis for the individual patient. Currently, it is the qualitative nature of pressure mapping that proves itself most useful as the graphical presentation of the pressure data allows the clinician to quickly determine the efficacy of the seating system in pressure relief.

Previously, the clinician gathered information regarding a patient's diagnosis, skin condition, seating needs, lifestyle, environment, and wound history and took this into account along with previous experience with similar patients and seating systems to make an educated guess to the best pressure relieving seating system for the patient (1, 3, 7, 8). Computerized pressure mapping allows the clinician to take that same information and actually see if the chosen seating system will provide the necessary pressure relief without waiting to see whether or not the patient develops skin problems.

Using Pressure Mapping Systems

The Seating Department of Shriners Hospital for Children in Tampa, FL, uses the pressure mapping system primarily as a tool for cushion selection for those children who have a history of or who are at risk for pressure-related skin problems. The list of patients ranges from those who may be physiological ambulators with a wheelchair for long-distance mobility to those who suffer from chronic pressure-related skin problems. The need to determine with relative certainty that a patient's seating system is providing adequate pressure relief is vital to possibly prevent pressure-related skin problems. (2,7).

Our current testing protocol includes taking a control reading as a datum for comparison and testing of various seat cushions in the patient's wheelchair. The control reading is taken by having the patient sit on a wooden evaluation table topped with a mat of two-inches of polyolefin foam with a removable vinyl cover. This planar vinyl surface stimulates a relatively uncushioned seating surface free of the pressure relieving and positioning effects on contouring and higher grade foam packages used in many seat cushions. The evaluation mat control sample also provides a datum for comparison between trials on the same patient. After the control reading is taken, the sensor mats placed on the seat cushion in the patient's wheelchair to determine the pressure relief properties of the current seating system. Once that pressure reading has been taken, the process of trying different seat cushions in the wheelchair and taking pressure mappings for each cushion begins. During each trial, the patient sits on the cushion with the mat in place for five to ten minutes before the trial begins in order to achieve a steady-state seated condition. Once we have reached a steady-state condition, we take our trial reading; and the trials are complete, we visually the data by looking at the plots side by side. We continue trying different cushions, taking trials, and comparing the data until we find a cushion that provides the optimal pressure relief.

As is visible in Figure 1 , (below), a color gradient scale represents the pressure values. Lower pressures are represented by the darker colors and higher pressures by the lighter colors with red designating the highest pressures. Using the pressure information, we can find the cushion that provides adequate pressure relief as well as meeting the other orthopedic needs of the patient. We can then prescribe that seat along with any necessary changes in the rest of the seating system. Once a durable medical equipment provider has delivered the new seating and other changes to the wheelchair, we conduct a follow-up evaluation in which we pressure map the patient with the changes to make sure that pressure relief provided by the new seating is still adequate.

Figure 1

Just as pressure mapping supplies the clinician with information in cushion selection, it can also be used to supply a funding source or other rehabilitation professionals with additional justification for a chosen seating system. As seating technology changes rapidly, it can be difficult to stay abreast of the different options for seating systems. Different materials have been developed for specifically for orthopedic seating systems, and various other materials have been introduced to the seating realm from other industries through technology transfer. Ever interested in providing the most versatile product for the lowest production cost and the best profit margin, seating companies develop new using these materials, making it difficult to stay current on the latest seating technology. Realizing the usefulness of pressure mapping data, many seating companies are now distributing pressure-mapping comparisons for their cushions against competing cushions. They hope the comparisons will be useful to the clinician in that they provide an initial evaluation of a seat cushion without having to try them on patients first. However, the lack of meaningful quantitative data from pressure mapping systems precludes results that will truly eliminate the need to try a patient on a seat. Still, when applied to the individual patient, graphical data from a pressure mapping can prove an objective comparison of the pressure relief efficacy of different seating systems.

Figure 2 , below, shows a sample pressure mapping session for a patient with spastic quadriplegic cerebral palsy. The patient has a significant lower extremity surgical history that includes bilateral adductor tenotomies and hamstring releases, bilateral hip varus derotational osteotomies and subsequent hardware removals one year later, and a right femoral shortening. They physical therapist's mat examination revealed a mild scoliosis and pelvic obliquity as well as a leg discrepancy of approximately 0.5-cm. Originally, the Shriners Hospital Seating Department had done a prescription for a custom seat cushion that could provide adequate positioning and pressure relief. However, that prescription was not used. Instead, a different prescription done by the patient's pediatrician, school physical therapist, and the durable medical equipment provider was used. In that prescription a plan 2i thick polyolefin foam seat cushion with a vinyl cover was selected.

Figure 2

When the patient returned to Shriners for a follow-up evaluation, he complained of pain and discomfort when sitting in the power wheelchair over time (reportedly, less than 30 minutes, according to the patient), and the patientis mother reported significant skin redness on the patientis buttocks. In Figure 2, we see that the planar vinyl seat cushion provided approximately the same pressure relief as the evaluation mat in the control trial. A J2 VariLite ProForm air seat cushion were used to stimulate the effects of custom contour and a softer sitting s urface on pr essure relief. The J2 and ProForm were not chos en as final opt ions for seat cushion as they lack the lateral stability required for the patient to maintain neutral pelvic positioning. The selected cushion,a Pin Dot Sil-houette custom seat cushion, was not available at the time of testing since it is custom made to order from an impression o f the pa tient. Still, we believe with much certainty that the custom contouring, a s ofter yet more resilient cushion material and a stretch Lycra cover would provide superior pressure relief to the planar vinyl seating system. As of the completion of this paper, we are aw aiting the durable medical equipment provider to de liver the new seat cushion at which time we will do another follow-up pressure mapping. Still, without the data from the pressure m appi ng system, we would not have had sufficient information to justify to the funding source that a new seat cushion was indeed medically necessary.

In addition to giving funding sources and clinicians' information about seating system, pressure mapping also allows the clinician to educate patients and caregivers as to the importance of pressure relief in a seating system. By being able to actually see the difference in pressure relief between different seating systems, patients can get a better idea of the importance of their seating in wound prevention. This is especially important for those patients with a significant pressure wound history. We have found that after our patients with chronic pressure-related skin problems and their caregivers have gone through a pressure mapping session, their compliance in using specialized pressure relief cushions even outside of the wheelchair increases. We have also seen that their incidences of skin breakdown due to improper pressure relief decreases, and most all of the patients and caregivers report that they now pay more attention to seating surfaces outside of the wheelchair.

By showing a patient or caregiver just what happens to sitting pressures during pressure relief exercises such as push-ups or forward leans, the clinician can more clearly express to the patient or caregiver the importance of the equipment or exercises. Currently, clinicians tell the patients how and why to perform pressure-relief exercises. However, if the patient does not fully understand the importance or efficacy of the exercises, she may not comply as fully as if she had a better understanding of their importance. By being able to see just what is happening with the pressures during pressure relief exercises, the patient can gain a better understanding of their efficacy, and both the patient and the clinician can make sure that the exercises are providing adequate pressure relief.

Pressure mapping systems also present a valuable tool for hospital and wound treatment center cost savings. Commercially available pressure mapping systems cost typically between $9,000 and $20,000, including the computer system, which is in rather sharp contrast to the $3,000 to $70,000 average cost treat pressure one sore (5). Taking that into consideration, the purchase of one pressure mapping system could easily pay for itself by preventing three minor pressure sores or one major one. Hospitals and wound care centers could prevent future pressure problems by pressure mapping those patients with chronic pressure-related skin problems or those patients at greatest risk. By using the data along with other clinical tools such as critical pathways (6), those patients who do have a risk can possibly have pressure sores prevented by more thorough charting of their risk and early intervention at the first signs of elevated sitting pressures. As at risk patients make regular return visits to their wound treatment centers, clinicians would interview and pressure map them to see if they are experiencing lifestyle or pressure changes that might lead to a wound. If the clinician notices elevated pressures, she can look to information from the interview or a physical examination for possible explanations (i.e. changes in diet or weight, smoking status, increased time in the chair, possible orthopedic changes, etc.). The patient can then be prescribed or issued a better pressure relief seat cushion to be used either permanently or until the regular seating system pressure maps as "sage" to use again.

It should also be noted that pressure mapping can only be effective in a preventative manner if accompanied by a thorough interview, which should be conducted with each pressure mapping. The pressure mapping will only show elevated seating pressures. It will not necessarily address why the pressures are elevated. Thus the interview becomes a very valuable part of the pressure mapping in that it can address other issues and factors which can possibly lead to skin breakdown.

CONCLUSION

While pressure mapping is not the final word in pressure wound prevention and management, it does provide us with a very useful tool. Its power lies in its ability to take an abstract concept, body-surface interface pressures, and graphically represents it to patients, caregivers, and clinicians. In that respect, it provides us with a good tool for education. At the same time, it provides us with a means to analyze what we previously were unable to in the attempt to possibly prevent pressure sores. The ability to do this would provide great cost savings to hospitals and wound care centers.

Further research needs to be done, however, in determining the absolute meaning of the pressure data. In order for the data to be deemed truly accurate and comparable between patients, the amount of hysteresis within the system must be minimized while its robustness is maximized. Also, a universal acceptable "safe pressure" range needs to be developed. With a tested and reliable acceptable safe pressure range, pressure data will gain much better value as pressure mapping comparisons between similar patients will have some actual numerical basis.

Pressure Mapping System Manufacturers Please note that this listing is not complete.

Crown Therapeutics
Belleville, IL
(800) 851-349
(618) 277-9173
www.crownthera.com

Novel Electronics
St. Paul, MN
(651) 221-0505
www.novel.de

Steridyne Corporation
Riviera Beach, FL
(800)327-6185
(561) 844-3486

Tekscan Boston, MA
(800) 248-3669
(617)464-4500
www.tekscan.com

Visa Medical
Winnipeg, Ontario
Canada
(800) 563-7676
(204) 949-7676
www.vistamedical.org

References:

 

    1. Ferguson-Pell, M. and Cardi, M. "Prototype Development and Comparative Evaluation of Wheelchair Pressure Mapping System." Assistive Technology 1993;78-91

 

    1. Ferguson-Pell, M.W.;Wilkie, I.C,; Reswick, J.B.; Barbenen, J.C, "Pressure Sore Prevention for the Wheelchair Bound Spinal Injury Pati-etn." Papaplegia 1980; 18: 42-51

 

    1. Henserson, J.L.; Price, S.H.; Brand-stater, M.E..; Mandac, B.R. "Efficacy of Three Measures to Relieve Pressure in Seated Persons with Spinal Cord Injury." Archives of Phy Med Rehab 1994;75:535-539

 

    1. Linddan, O.; Greenway, R.M.; Piazza, J. "Pressure Distribution on the Surface of the Human Body : I Evaluation in Lying and Sitting Positions Using 'Bed of Springs and Nails."' Archives of Phys Med Rehab 1965; 46: 378-386

 

    1. Lubin, B. and Powell, T. "Pressure Sores and Specialty Beds: Cost Containment and Assurances of Quality of Care." Journal of Enterostomal Theraphy 1990; 18:190-197

 

    1. Mosher,C.M. "Putting Pressure Ulcers on the Map." Journal of Wound Care Society 1995, 22:183-186

 

    1. Rosenthal, M.J.; Felton, R.M.; Hileman, D.L,; Lee, M.; Friedman, M.; Navach, J. "A Wheelchair Cushion Designed to Redistribute Sites of Sitting Pressure." Archives of Phy Med Rehab 1996; 278-282

 

  1. Shapcott , N. and Levy, B. "By the Numbers: Making the case for clinical use of Pressure Measurement Mat Technology to prevent the development of pressure ulcers." Team Rehab Report Jan.1999: 16-21