P ressure ulcers are all-too-often an outcome of acute and chronic illness. They occur across the continuum of care and their prevalence among patients in acute care ranges from 3.5% to 29.5%.1,2
Determining prevalence can be useful for benchmarking over time. Serial prevalence audits can serve as a pressure ulcer outcomes-management tool, reflecting the way changes in practice affect pressure ulcer prevention and treatment. One way to impact the prevention and treatment of pressure ulcers is through allocation of resources, specifically implementation of support surfaces.

Literature Review
The role of mechanical forces on the development of pressure ulcers has long been recognized. Many investigators3-7 have measured the relative contribution of shear and pressure in diminishing blood flow. Considerable investigation has concluded that a relationship exists between external pressure loading and tissue damage. Shear also has been identified as a major mechanical force that causes tissue damage; specifically, an inverse relationship exists between pressure and shear. As the amount of shear increases, the amount of pressure required to cause pressure ulcers is reduced.
Utilizing support surfaces is one way to impact the prevention and treatment of pressure ulcers.8 The Agency for Health Care Policy and Research (AHCPR) guidelines recommend that patients at risk for the development of pressure ulcers should be placed on pressure-reducing support surfaces.9 One acute care facility used serial prevalence audits to determine the effect of a new support surface protocol on the number of nosocomial pressure ulcers.10
When evaluating the efficacy of a support surface, measuring its ability to relieve direct downward pressure and shear pressure is important. The pressure-relieving capability of a support surface added to a multiple of its ability to relieve shear yields a measurement of the major mechanical forces that are known to cause pressure ulcers. This relationship between pressure and shear has been referred to as the "isolibrium factor".11
In 1999, a new technology became available in the support surface market with the introduction of ISOFLEXR (Gaymar Industries, Inc, Orchard Park, NY). The pressure and shear management technology consists of a grid-like matrix of vertical columns constructed of an elastomer material. A column design manages pressure by redistributing a patient's weight; thereby, optimizing low tissue interface pressures. Additionally, this support surface has the ability to reduce shearing forces in the supine and Fowler positions.

Purpose
A study was conducted to compare prevalence rates, the number of patients with hospital-acquired pressure ulcers, and the total number of facility-acquired pressure ulcers before and after a hospital-wide change in support surfaces. The goal was to determine if a change in support surface technology would impact the occurrence of facility-acquired pressure ulcers. Implementing the new pressure and shear management support surface was the only change in practice in the period of time between the first and second prevalence audits.

Methods
Subjects and setting. The study facility is a 243-bed acute care medical center in rural northeastern Pennsylvania. All individuals hospitalized on five medical-surgical units and two intensive care units on each of the study days were eligible to participate. One hundred, nine (109) inpatients (two African American and 107 Caucasian patients) participated in the first audit in June 1999, and 128 (one African American and 127 Caucasian patients) inpatients participated in the second audit in October 2000.
Instruments. The two primary investigators, certified wound, ostomy, and continence nurses (CWOCNs), designed the data collection tool. The tool included the following variables: patient identifier, number of pressure ulcer(s), stage of pressure ulcer(s), and location of pressure ulcer(s). The pressure ulcer staging system utilized was recommended for universal use by the AHCPR.9
Procedures. The primary investigators were responsible for all data collection. They assessed the skin integrity of each subject participating in each pressure ulcer prevalence audit. Although skin assessment is one component of daily nursing evaluation of patients at this facility, verbal permission was obtained from each patient. No patients refused to participate in either audit.
Prevalence was determined using the following point prevalence formula12:
number of individuals with a pressure ulcer(s)on the day of the audit/number of individuals assessed on the day of the audit
Patients with facility-acquired pressure ulcers were identified through a review of the medical charts to determine if the ulcer was documented on the admission database. Chart reviews also provided the demographic, diagnostic, and census data (see Tables 1, 2, 3).
The facility's nursing protocols for pressure ulcer management consisted of assessing a patient's level of risk for developing a pressure ulcer on admission utilizing the Braden Risk Assessment Tool.13 Implementation of prevention protocols was determined by a patient's assessed level of risk (low risk: 15 or greater, moderate risk: 13 to 14, high risk:12 or less) (see Figure 1).
The Braden Risk Assessment was repeated at specific intervals throughout the patient's hospital stay (low risk Q24o, moderate risk Q24o, and high risk Q8o); prevention measures were adjusted accordingly. All nurses caring for patients had received education and training on how to use the Braden Risk Assessment Tool and how to implement prevention protocols.
Only ulcers with a pressure etiology were identified, quantified, and staged during the prevalence audits. Ulcers were identified as facility-acquired (nosocomial) or previously existent.
Following the first audit in June 1999, four different support surfaces were evaluated in the facility. The study support surfaces were chosen and implemented throughout the facility to replace traditional foam mattresses. No other changes were made in the pressure ulcer management protocol. In October 2000, 3 months after implementing the study support surfaces, a second audit was conducted using the same methodology.
Exclusion criteria. Pediatric, obstetric, and psychiatric patients were excluded in both audits. Only pressure ulcers were included; all other ulcers and skin impairments were excluded from the study.

Results
Pressure ulcer prevalence was 8.3% in June 1999, and 7.8% in October 2000; whereas, the prevalence of nosocomial pressure ulcers was 5.5% in 1999 and 3.1% in October 2000 (see Table 4). Facility-acquired pressure ulcers also were compared by stage and site (see Table 5). Overall, an 88% decrease in the percentage of Stage II pressure ulcers occurred between the 1999 and 2000 audits.

Discussion
To decrease the occurrence of facility-acquired pressure ulcers in their hospital, CWOCNs initiated the process of changing the hospital's support surface utilization. The change consisted of implementing a new pressure and shear management system. After evaluating four different support surfaces, the study support surface was selected based on its construction, performance, and extended life expectancy. The new surfaces replaced traditional foam mattresses throughout the hospital with the exception of the pediatric, obstetric, and psychiatric units. A comparison of two inpatient groups showed that the facility-acquired pressure ulcers were decreased by 53%, from 15 facility-acquired pressure ulcers in the first audit to seven facility-acquired pressure ulcers in the second audit.
An acute care facility has no control over the occurrence of pressure ulcers patients present on admission, but healthcare professionals can impact the occurrence of pressure ulcers acquired during hospitalization by implementing a high standard of pressure ulcer prevention and treatment. Effective support surfaces are an important way to improve the outcome of pressure ulcer management. In this case, a clinically significant decrease in the number of pressure ulcers that developed during hospitalization was achieved by implementing a new pressure and shear management support surface.

Limitations
The limitations of point prevalence studies are well known and using two different patient populations decreases the methodological strength of this study. A comparison of other variables such as patient acuity, staffing patterns, and time spent on the operating table would strengthen the conclusions of this study. Although the only component that was changed in the pressure ulcer management protocol was the support surface, other factors, including the Hawthorne effect, also may have influenced the outcomes observed.

Conclusion
Prevalence rates provide a "snapshot" view of the number of patients with pressure ulcers present on a specific day in a facility. Comparing other measurements such as the number of patients with facility-acquired pressure ulcers and the total number of pressure ulcers adds to the clinical picture. Implementing a new support surface appeared to have helped decrease the number of facility-acquired pressure ulcers by 53% in this acute care population, underscoring the fact that pressure relief adds to pressure ulcer prevention. - OWM