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Pressure-redistributing cushions: the Cinderella of support surfaces?

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VOL: 98, ISSUE: 08, PAGE NO: 59

Michael Clark, PhD, is senior research fellow, Wound Healing Research Unit, University of Wales College of Medicine, Cardiff

Successful prevention and treatment of pressure ulcers has become closely associated with the correct selection and use of pressure-redistributing (PR) support surfaces. Many authors have evaluated the performance of various support surfaces - a search of the electronic database Medline for material on pressure ulcers published in 2000 identified 230 references, and of these 12.6% (n=29) focused on support surfaces. However, one group of support surfaces appears to be under-represented within these studies. Only seven (3%) of the publications reported the use or evaluation of PR seat cushions.

Successful prevention and treatment of pressure ulcers has become closely associated with the correct selection and use of pressure-redistributing (PR) support surfaces. Many authors have evaluated the performance of various support surfaces - a search of the electronic database Medline for material on pressure ulcers published in 2000 identified 230 references, and of these 12.6% (n=29) focused on support surfaces. However, one group of support surfaces appears to be under-represented within these studies. Only seven (3%) of the publications reported the use or evaluation of PR seat cushions.

The apparent neglect of seat cushions as part of the armoury in the struggle against pressure ulcers has long been anecdotally reported through observations that patients are often seated on ordinary chairs during the day while the nearby bed has a sophisticated PR mattress. How widespread is this phenomenon?

In 1983 David et al reported the patterns of resource use among 961 patients with established pressure ulcers. This cohort of patients experienced a total of 1,506 pressure ulcers, almost 60% of which were full-thickness wounds (grades 3 and 4), yet only 41.5% were nursed on various mattresses and beds. A slightly higher proportion (43.3%) was allocated some form of seat cushion. However, the appropriateness of many of these cushions was questionable.

Table 1 highlights the types of cushion allocated to people with pressure ulcers, with the most prevalent surfaces being Sorbo-rings and sheepskin pads. The Sorbo-ring, which was common across the NHS in the late 1970s and early 1980s, consisted of a latex foam or rubber ring and resembled a doughnut. The disappearance of this and similar air-filled products is often considered to represent the translation of research into practice.

Crewe (1987) reported an observational study in which 70 elderly hospital patients were asked to sit for a week on one of 17 cushions (five polyester silicone padding, one 'particle-filled', one foam and water combination, six polyurethane foam, two latex foam blocks and two ring cushions). Forty-six subjects completed at least one week's use of a cushion. They were then allocated a second cushion for another week, then a third and so on up to a maximum of four weeks' participation in the study.

Over the duration of the observations, the 46 subjects sat on various cushions for a total of 87 person-weeks. Before cushion use they experienced a total of 72 pressure ulcers, 24 (33.3%) of which were described as 'breaks in the skin'. However, no grading system was used to further classify these breaks. Over the varying times subjects sat on the cushions 27 new pressure ulcers developed or their existing ulcers deteriorated.

Interpretation of the distribution of deteriorating or new pressure ulcers is greatly hampered by the uncontrolled study design and lack of detailed reporting of skin outcomes. However, all nine subjects who sat on the ring cushion experienced new or deteriorating natal cleft ulcers, while five also experienced new or deteriorating sacral pressure ulcers. This study led to the rapid disuse of ring cushions across the NHS.

Hawthorne and Nyquist (1987) also reported the use of cushions and mattresses among hospital patients with established pressure ulcers. This survey (Table 2), conducted in 1986, shows that the widespread use of the Sorbo-ring continued across UK health care before Crewe's publication the following year. However, Nyquist and Hawthorn (1985) suggested that greater numbers of patients with pressure ulcers were allocated a PR mattress compared with those allocated a cushion. Of the 132 patients surveyed, 51 had been allocated a mattress and 40 a seat cushion (mainly Sorbo-rings). As use of the Sorbo-ring declined during the late 1980s, the disparity between the numbers of patients allocated a mattress or cushion widened, with the emphasis in the early 1990s being firmly on the mattress. This gap between the number of patients allocated mattresses or cushions may well reflect the discontinued use of cushions such as the Sorbo-ring without their replacement with more appropriate cushions.

The lack of focus on seat cushions can be seen in national surveys of PR devices conducted during the 1990s. St Clair (1992) reported a national survey of the pattern of use of one PR mattress. Data was gathered across 119 hospitals and hospices on 788 people nursed on the mattress. Of the total sample, 428 had established pressure ulcers, with 276 sitting out of bed each day. Most subjects who sat out of bed spent more than two hours each day sitting on unspecified surfaces. While St Clair clearly considered time spent out of bed to be an important variable, there was no information provided about whether PR cushions were used, what types were in use and in what numbers.

This focus on the mattress in large surveys of the use of support surfaces continued through the 1990s. Winman and Clark (1997) reported on the pattern of use of 329 PR mattresses, with 74% used in UK hospitals. Similar to St Clair's population, most patients sat out of bed each day (n=257, 78.1%), many (n=135) for over four hours. Most of the seated patients had no special PR cushion (n=151, 58.8%). Where cushions had been allocated, 44 different types were in use, with many used in single cases (24 of the 44 cushions were only allocated to a single patient). However, Winman and Clark did not report which types of cushion were used, preferring to focus on the apparent lack of clarity regarding which cushions were effective, given the large number of different cushions encountered during their survey.

Were Winman and Clark correct to infer that health care practitioners had insufficient evidence with which to identify effective PR cushions? It is generally accepted that the efficacy of an intervention is best explored through its inclusion in a randomised controlled trial (RCT). To date only three RCTs have explored the use of PR cushions to either prevent or heal pressure ulcers.

The first RCT to explore the role of cushions in pressure ulcer prevention compared two foam wheelchair cushions. One was a foam block and the other was the same foam but with a contoured surface (Lim et al, 1988). The study recruited elderly wheelchair users (over 60 years old), all of whom were free from pressure ulcers for at least two weeks preceding recruitment into the study. Eligible subjects also had to be able to sit for at least three hours each day. In total 52 subjects completed the study, and of these 37 developed pressure ulcers, with a total of 72 ulcers reported. None of the ulcers presented as full-thickness wounds, with the majority being areas of persistent erythema located over the ischial tuberosities. There was no significant difference between the incidence of pressure ulcers on the two cushions.

In a similar investigation, Geyer et al (2001) reported a pilot investigation comparing different wheelchair cushions. The control arm were allocated a three-inch thick foam cushion with convoluted surface, while the research subjects were allocated unspecified 'commercial cushions' with fitted incontinence covers. Eligible subjects were recruited from the population of two nursing homes. They were at least 65 years old with no pressure ulcers on the pelvic region, considered to be vulnerable to developing pressure ulcers (low Braden score with low combined mobility and activity sub-scales), able to sit for at least six hours each day and had a body weight under 250lb.

Subjects were randomly allocated and all outcome measures were gathered by observers blinded to the treatment allocation. Weekly assessments of subjects' skin and their risk score were performed, with each subject's participation in the study ending with either the development of a pressure ulcer over the pelvic region, death, transfer to another health care institution or at an (unspecified) time after recruitment. In this pilot study, 17 subjects were recruited to the control group, with 15 receiving the 'commercial cushions'. Only nine reached the unspecified study termination date, five were discharged, while one subject died in each arm of the study.

Pressure ulcers developed in 50% of subjects; the severity of the ulcers was not reported. Interestingly there was a difference in the anatomical distribution of pressure ulcers between subjects within the two groups. The control subjects developed eight ischial tuberosity pressure ulcers and two at other pelvic areas. In contrast, the experimental group did not develop any pressure ulcers over the ischial tuberosities, with all six ulcers affecting other pelvic sites.

Both RCTs that explored the incidence of new pressure ulcers on PR cushions have identified high incidences (over 50%) of ulcers, which were mainly superficial (Lim et al, 1988). The high incidence of new ulcers infers that sound RCTs comparing pressure ulcer incidence on different cushions could be undertaken with relatively small patient populations and, consequently, comparative information about cushion efficacy could be obtained without recourse to lengthy and expensive data collection.

Only one RCT has compared the rate of healing of pressure ulcers on PR cushions (Clark and Donald, 1998). Subjects were drawn from hospital wards and nursing homes, with eligibility based on age (over 65 years), the presence of partial or full thickness pressure ulcers over the sacrum or ischial tuberosities with a surface area of 2-15cm2, being at moderate to high risk of developing further ulcers, able to sit for at least two hours each day and having a serum albumin level of >2.5mg/dl.

All data collection was conducted unblended at weekly intervals with a blinded analysis of the skin outcomes and other data. Each subject was allocated a dynamic mattress for use when in bed. Subjects remained in the study until their pressure ulcers healed, they were discharged or died, became unable to sit for two hours each day or experienced debridement of their pressure ulcers. Twenty-five completed at least one assessment. During the investigation eight subjects experienced complete healing of their pressure ulcers.

The three RCTs that have compared seat cushions have not provided much guidance for practitioners seeking to prescribe the most effective cushion. Pressure ulcer incidence rates within cushion controlled studies are high, with over 50% of all subjects recruited developing pressure ulcers. Does this infer that cushions may not be helpful in preventing tissue damage? Clearly further studies are required to fully evaluate the role of PR seat cushions in pressure ulcer prevention.

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