This clinical trial demonstrated significant differences in pressure ulcers occurring over the ischial tuberocities between segmented foam and skin protection wheelchair cushion groups. The study is the first clinical trial to test the effectiveness of wheelchair seat cushions while controlling for the effects of the wheelchair. Controlling for the wheelchair is important because poorly fitting wheelchairs are likely to result in poor posture (e.g., posterior pelvic rotation, pelvic obliquity) that will result in higher pressure and increased pressure ulcer risk. In other words, both poor posture and inadequate immersion and envelopment by the cushion can lead to prolonged ischemia-inducing pressure and shear that is believed to be the primary factor leading to pressure ulcer development. The provision of a properly fitted wheelchair to both control and treatment arms of the study was intended to reduce the chance that poor posture would cause the pressure ulcer and allow for the effect of the cushion properties to be compared.
The incidence rates for pressure ulcers near the ischial tuberosities were lower than we anticipated prior to the trial. Several factors may have contributed to this result. In the control group, the segmented foam cushions may have performed better in preventing pressure ulcers than we had anticipated. In our pilot14
we used egg crate foam cushions as a control because they represented the standard-of-care cushion at the time. By the time we developed this full-scale trial, the standard-of-care had shifted to the cushions represented by the segmented foam cushion used here. We may have underestimated the improvement that the segmented foam provided. To roughly compare the relative effectiveness of the segmented foam cushion of this trial to the egg crate foam cushion from our pilot study, we can compare the rate of combined IT and sacral/coccyx ulcers in the larger trial, 17.6%, to the rate in the pilot, 58%, to see that there is a large difference.
The intervention protocol used for the participants of this study may not represent the current practice in nursing homes. The protocol was designed to isolate the effect of the cushion while optimizing other pressure ulcer related seating variables. For example, wheelchair fit and function was monitored and adjusted regularly to avoid problems such as missing foot and arm rests, malfunctioning brakes, loose upholstery, etc. that could have contributed to increased pressure ulcer risk had these issues gone unattended for a long period of time. In other words, applying the control necessary for performing the RCT, the effective risk level of the cohort may have been lowered. This is another possible explanation as to why the overall IT pressure ulcer incidence rate was lower than we anticipated. Although the frequency of maintenance issues was not recorded, we performed a large number of wheelchair and cushion adjustments during this study and recommend that more attention be paid to wheelchair and cushion maintenance and fit in nursing homes.
A second, notable difference between our study protocol and current practice in nursing home wheelchair seating services concerns the use of pressure mapping to assist in the selection of skin protection wheelchair cushions. Our protocol specified that the seating assessment use pressure mapping as a tool to help guide the selection of a cushion in the treatment group. All other aspects of the assessment process were the same for both groups. Therefore, our study and its results compare the use of a SFC to the use of a SPC under conditions where the seating assessment incorporated pressure mapping in the skin protection cushion selection process. The assessment protocol, including pressure mapping for cushion selection, represents best practices for this population.
The severities of pressure ulcers observed on the ITs were stage 1 (n=1), stage 2 (n=7) and unstageable (n=1). Since an IT pressure ulcer was an endpoint in the study, we could not follow up to record if and how these wounds progressed after this first observation. The incidence of sacral pressure ulcers was not a defined study endpoint hence the recorded severity of the ulcers in this category reflected the worst condition that these wounds would assume before a study endpoint.
Based on the results of this study and our experience providing seating and wheeled mobility interventions in nursing homes, we recommend that nursing home residents be assessed for their risk of developing pressure ulcers. Those residents that are determined to be at high risk as determined by the Braden Scale score and who use a wheelchair as their primary means of mobility should be provided with a wheeled mobility and seating assessment and properly fitted wheelchair with a skin protection cushion. The economic impact of such interventions still needs to be studied and should follow from this investigation focused on clinical outcomes.
Support surface and posture conditions were only controlled for periods of time when the participants were sitting in their wheelchairs. The study did not attempt to control conditions that may have affected pressure ulcer risk while the participants were in bed or on other support surfaces. This may have had an effect on the combined IT and sacral ulcer results since this lack of control introduced uncertainty regarding the loading condition that may have contributed to the sacral pressure ulcers. Pressure and shear could have been applied to the sacrum when a participant was in either the lying or sitting positions. The pressure ulcer incidence rate may have been affected by possible nursing home staff awareness of residents’ participation in the study. This effect was likely the same for both randomization groups. Finally, our sample was primarily female and white and may not be representative of the entire nursing home, elderly population.