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5. Committee on Safety of Medicines. Current Problems in Phar- macovigilance. (29). 2003. Medicine and Healthcare Products Regulatory Agency.

6. Stamm WE. Criteria for the diagnosis of urinary tract infection and for the assessment of therapeutic effectiveness. Infection 1992; 20(Suppl 3): S151–4.

7. Stothers L. A randomized trial to evaluate effectiveness and cost effectiveness of naturopathic cranberry products as prophylaxis against urinary tract infection in women. Can J Urol 2002; 9: 1558–62.

8. Kontiokari T, Sundqvist K, Nuutinen M, Pokka T, Koskela M, Uhari M. Randomised trial of cranberry-lingonberry juice and Lactobacillus GG drink for the prevention of urinary tract infections in women. BMJ 2001; 322: 1571–3.

9. Nicolle LE. Urinary tract infections in long-term care facilities. Infect Control Hosp Epidemiol 1993; 14: 220–5.

10. Winickoff RN, Wilner SI, Gall G, Laage T, Barnett GO. Urine culture after treatment of uncomplicated cystitis in women. South Med J 1981; 74: 165–9.

11. Howell AB, Foxman B. Cranberry juice and adhesion of antibiotic-resistant uropathogens. JAMA 2002; 287: 3082–3.

12. Jepson RG, Mihaljevic L, Craig J. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev 2004; 1: CD001321.

Received 28 May 2004; accepted in revised form 29 December 2004

Age and Ageing 2005; 34: 261–267  The Author 2005. Published by Oxford University Press on behalf of the British Geriatrics Society. doi:10.1093/ageing/afi057 All rights reserved. For Permissions, please email: [email protected] Published electronically 11 March 2005

Effectiveness of an alternating pressure air mattress for the prevention of pressure ulcers KATRIEN VANDERWEE, MARIA H. F. GRYPDONCK, TOM DEFLOOR

Nursing Science, Department of Public Health, Ghent University, UZ 2 Blok A, De Pintelaan 185, B 9000 Gent, Belgium

Address correspondence to: K. Vanderwee. Fax: (+32) 9 240 50 02. Email: [email protected]

Abstract

Background: studies of the effectiveness of alternating pressure air mattresses (APAMs) for the prevention of pressure ulcers are scarce and in conflict. Objective: evaluating whether an APAM is more or equally effective as the standard prevention. Design: randomised controlled trial. Setting and subjects: patients admitted to 19 surgical, internal, or geriatric wards in seven Belgian hospitals were included if they were in need of prevention of pressure ulcers. To define this need, two methods were used randomly: the Braden Scale or the presence of non-blanchable erythema (NBE). Methods: 447 patients were randomised into either an experimental or a control group. In the experimental group, 222 patients were lying on an APAM (Alpha-X-Cell®, Huntleigh Healthcare, UK). In the control group, 225 patients were lying on a visco-elastic foam mattress (Tempur®, Tempur-World Inc., USA) in combination with turning every 4 hours. Both groups had identical sitting protocols. Results: there was no significant difference in incidence of pressure ulcers (grade 2–4) between the experimental (15.6%) and control group (15.3%) (P = 1). There were significantly more heel pressure ulcers in the control group (P = 0.006). There was an interaction effect between the risk assessment method and preventive measures for the development of all pressure ulcers and sacral pressure ulcers. Conclusion: fewer patients developed heel pressure ulcers on an APAM. Patients identified as being in need of prevention based on the presence of NBE had a tendency to develop fewer pressure ulcers on an APAM. Patients identified as being in need of prevention, based on the Braden Scale, appeared to develop more sacral pressure ulcers on an APAM.

Keywords: decubitus ulcer, prevention and control, randomised controlled trial, beds, elderly

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Introduction

Pressure ulcers are serious complications of hospitalisation that need to be prevented whenever possible. A pressure ulcer is an area of localised damage to the skin and the underlying tissue caused by pressure and shearing forces [1]. Effective preventive measures reduce the intensity and/or the duration of pressure and shearing forces. Pressure- relieving mattresses, cushions and postures reduce the intensity of pressure and shearing forces [2]. APAMs and repositioning reduce the duration of pressure and shearing forces [3]. APAMs generate alternating high and low inter- face pressure between the body and support, by alternating inflation and deflation of air-filled cells [4].

APAMs have not been studied intensively. Using an extended PubMed (1965–2004) search, 16 studies were identified. Eight randomised controlled trials (RCTs) were relevant to the subject of this study. Five studies reported no statistical difference in the effectiveness of APAMs and various constant low-pressure devices [5–9]. In the other RCTs, a significant difference was observed [10–12]. The relative benefits of alternating pressure and constant low- pressure devices are unclear [4, 13].

Besides APAMs, repositioning is another commonly used strategy to reduce the duration of pressure and shear- ing forces. Although repositioning is generally accepted, there is scant evidence in the literature regarding the effec- tiveness of turning. Turning every 4 hours on a visco-elastic foam mattress (in combination with pressure-reducing posi- tions) is recommended by the Belgian and Dutch pressure ulcer guidelines [14, 15].

The aim of this study was to determine whether an APAM is more or equally effective than standard preven- tion. An RCT in an acute care setting was considered the most appropriate design to assess the effectiveness of an APAM in preventing pressure ulcers.

Methods

Subjects and recruitment

The RCT was carried out between May 2000 and August 2002 in 19 surgical, internal medicine, and geriatric wards in seven Belgian hospitals. Each nursing ward took part in the study for 20 weeks. Inclusion criteria were: > 18 years, expected hospitalisation stay at least 3 days, no grade 2, 3, or 4 pressure ulcer lesions [16] on admission, body weight <140 kg, and no contraindication for turning due to medical reasons. None of the included patients had scars of previ- ous pressure ulcer lesions. Patients were included if they were considered in need of preventive measures. To define this need, two methods were randomly used. The patient’s risk status was defined using either the Braden Scale [17] or the presence of a grade 1 pressure ulcer (non-blanchable erythema or NBE). The Braden Scale defines whether a patient is at risk of developing pressure ulcers. The scale consists of six subscales: sensory perception, moisture, activity, mobility, nutrition, and friction and shear. The total score ranges from 6 to 23 [17]. Patients with a Braden Scale

score <17 were considered at risk [1, 14, 15]. The predictive validity of this scale has been tested in several studies [18, 19]. Preventive measures were started on other patients based on the presence of NBE [14, 15, 20]. These two methods were applied, since both are commonly used in clinical practice and are recommended by the Belgian Pressure Ulcer Guidelines [14].

Approval for this study was granted by the ethics committee of Ghent University Hospital and of each parti- cipating hospital.

Intervention

In the experimental group, patients were lying on an alter- nating pressure overlay (Alpha-X-Cell®, Huntleigh Health- care, UK). No turning protocol was used. Since the principle of an APAM is to alternate the pressure points on the patient [3], theoretically, repositioning is not necessary. In the control group, a standardised prevention protocol was used. Patients were lying on a visco-elastic polyethyl- ene–urethane foam mattress (Tempur®, Tempur-World Inc., USA) in combination with a standardised turning pro- tocol every 4 hours. The following sequence of position changing was used: semi-Fowler 30°, right-side lateral posi- tion 30°, semi-Fowler 30°, left-side lateral position 30°[2]. In both groups the heels of the patients were elevated from the mattress by placing an ordinary cushion beneath the lower legs [1, 14, 21]. The sitting protocol was standardised and identical in both groups. When patients were seated in a chair, an air cushion (Airtech®, Huntleigh Healthcare, UK) was used for all patients. They were also asked to stand up every 2 hours, alone or with help. If the back of the chair could be tilted backwards, the patient’s legs were put on a footrest. If the back of the chair could not be adjusted, the patient’s feet were placed on the floor [22].

Based on a 12% incidence of pressure ulcers (grade 2 or higher) in hospitals, a sample size was calculated of 223 patients (in each group) to detect a difference of 7% in the incidence of pressure ulcers between the experimental and control group (α = 0.05; power = 80%). Data collection

The occurrence of pressure ulcers was assessed daily by ward nurses. An additional daily inspection of the skin by a researcher was felt to be an unnecessary burden for patients. A random sample of patients was observed at unexpected moments by both the researcher and the data nurse. Pres- sure ulcers were classified according to the four grades of the European Pressure Ulcer Advisory Panel (EPUAP) [16]. In order to standardise distinguishing between blanchable and non-blanchable erythema, a 4 cm × 4 cm transparent pressure disk was used. The nurse pressed the transparent disk on the erythema. If the erythema blanched, it was defined as blanchable erythema. If the erythema remained while pressing, it was defined as NBE [23, 24]. In addition, a Braden score was obtained for all patients on admission and every 3 days thereafter [17].

A data nurse was responsible for the follow-up of the study on each ward. Once a week, the nurse scored the skin condition and the Braden Scale of a randomly selected

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sample of patients. This was carried out unannounced and independently of the other nursing staff. The researcher car- ried out similar observations independently once a week. The inter-rater reliability for the classification of pressure ulcers between researcher, nursing staff, and data nurse ranged from κ = 0.88 (95% CI 0.78–0.97) to κ = 0.94 (95% CI 0.91–0.97). The inter-rater reliability for scores on the Braden Scale was also high. Kappa varied from 0.78 (95% CI 0.74–0.82) to 0.87 (95% CI 0.82–0.95).

Statistical analysis

The sequence of allocation to the experimental or control group was determined beforehand based on randomisation tables generated with the SPSS 10 software package [25]. Serially numbered, closed envelopes were made for each participating ward. The envelope with the lowest number was opened upon admission of a new patient.

The Mann–Whitney U test was used for continuous var- iables that were not normally distributed and for categorical variables. Fisher’s exact test, and the χ2 test were used for categorical variables. A logistic regression analysis and Kap- lan–Meier survival analysis were performed to evaluate the effect of the prevention protocol on the incidence of pres- sure ulcers (grade 2 or higher) [19, 26]. All analyses were done with the SPSS 10 software package [25]. A value of P < 0.05 was considered statistically significant.

Results

Of the 2,608 patients who were admitted to the participat- ing wards during the study period, 570 met the inclusion cri- teria, of whom 123 patients gave no informed consent. In total, 447 patients were included in the study (Figure 1). The median age was 82 years (interquartile range 77–88 years), 93% of the patients were older than 65 years and 30% were older than 85 years. None of the patients had a dark skin. Random allocation of the 447 patients admitted to the study resulted in 222 patients in the experimental group (APAM) and 225 patients in the control group, respectively (Figure 1). Table 1 shows the baseline characteristics of the APAM and control groups. Since the groups were similar in all charac- teristics except for medical speciality, this variable is adjusted for in the analysis.

In the APAM group, 34 (15.3%) patients developed a pressure ulcer (grade 2–4). That figure was 35 patients (15.6%) in the control group. The incidence rate was 1.46 (34/2,371 days) (95% CI 0.98–1.97) in the APAM group and 1.66 (35/2,106 days) (95% CI 1.11–2.21) in the control group. Univariate analysis showed no difference in the inci- dence of pressure ulcers (grade 2–4) between the APAM and control group (P = 1, Fisher’s exact test). Using a logistic regression analysis, the effect of the prevention protocols on the incidence of pressure ulcers (grade 2–4) was evalu- ated, adjusting for four variables: length of stay, medical speciality, risk assessment method, and learning effect (Table 2). The learning effect of the nursing staff in execut- ing the prevention protocol was studied by comparing the first 10 weeks that a ward participated in the study and the last 10 weeks. There was a statistically significant interaction

effect between risk assessment method and prevention pro- tocol (Wald χ2 = 5.25; df = 1; P = 0.02). Therefore, a separate logistic regression analysis was performed for the Braden group (patients identified as being in need of preventive measures based on the Braden Scale) and the NBE group (patients identified as being in need of prevention based on the presence of NBE). These logistic regression analyses revealed no significant difference between the APAM group and the control group in the occurrence of grade 2–4 pres- sure ulcers (Table 2).

To eliminate the possible influence of sitting, despite the standardised sitting protocol, a logistic regression was per- formed including only bed-bound patients (n = 149). There was no interaction effect between the risk assessment method and the prevention protocol. The incidence of pres- sure ulcers was not different between the APAM group and the control group (Wald χ2 = 0.688; df = 1; P = 0.41).

A significant difference was found in the location of pressure ulcers between the two groups (P = 0.003; Fisher’s exact test). In the APAM group, 25 patients (73.5%) had a pressure ulcer on the sacrum, five (14.7%) on the heels, and

Admitted to the wards (n = 2,608)

Excluded (n = 2,038)

< 3 days admitted (n = 242)

> 140 kg (n = 3)

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P.U. grade 2, 3, or 4 on admission (n = 131)

Not at risk (n = 1,549)

Randomised (n = 447)

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PU n=16

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(n =148)

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Risk assessment by the presence of NBE

a (n = 150)

PU n=19

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PU c

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No PU n =122

Control group (n = 149)

Eligible for the study (n = 570)

Figure 1. Flow of patients through the trial. aNBE, non-blanch- able erythema; bAPAM, alternating pressure air mattress; cPU, pressure ulcer.

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four (11.8%) on another location. In the control group, 19 patients (54.3%) had a pressure ulcer on the sacrum and 16 (45.7%) on the heels. A separate Fisher’s exact test for each location revealed only statistical significance for the heels (P = 0.008; Fisher’s exact test). A logistic regression was performed with heel pressure ulcers as outcome to adjust for length of stay, medical speciality, risk assessment method, and prevention protocol variables. There was no interaction between risk assessment method and prevention protocol. In the APAM group, significantly fewer patients developed a heel pressure ulcer compared to the control group (Wald χ2 = 7.533; df = 1; P = 0.006).

The same logistic regression analysis was performed that included only patients with sacral pressure ulcers. There was a statistically significant interaction effect between risk assessment method and prevention protocol (Wald χ2 = 5.675; df = 1; P = 0.02). Patients identified as being in need of preventive measures based on the Braden Scale tend to develop more sacral pressure ulcers on an APAM than on a visco-elastic mattress (OR 2.77, 95% CI 1.00–7.69). The difference approached significance (P = 0.05). The separate logistic regression analysis for the NBE group revealed no significant difference (P = 0.34).

There was a significant difference in severity of pressure ulcers between the two groups (Wald χ2 = 4.503; df = 1; P = 0.034). Of the patients with pressure ulcers, in the APAM group 26 (76.5%) patients developed a grade 2 pressure ulcer and eight (23.5%) patients developed a grade 3 or 4 pressure ulcer. In the control group, 33 (94.3%) patients developed a grade 2 pressure ulcer and two (5.7%) a grade 3 or 4 pressure ulcer. In the subgroups the difference was not significant.

Using a Kaplan–Meier survival analysis, the time to develop a pressure ulcer was analysed between patients lying on an APAM and patients lying on a visco-elastic mattress. There was no significant difference between the two prevention protocols (log rank test =0.021, df=1, P =0.65). Adjusted for the risk assessment protocols, survival analysis also revealed no signi- ficant difference (log rank test =0.02, df =1, P =0.66).

Discussion

Despite a strict execution of recommended preventive mea- sures, a substantial percentage (15.4%) of the patients ident- ified as being at risk developed a pressure ulcer. The overall incidence of pressure ulcers was 2.6% (n = 69/2,608).

In the present study, the incidence of pressure ulcers was comparable in patients nursed on an APAM and those nursed on a visco-elastic mattress in combination with turning every 4 hours. This finding accords with previous studies on APAMs and constant low-pressure devices [5–9]. However, patients in the APAM group seemed to develop more severe pressure ulcers than those in the control group. Due to the limited numbers of patients, we must be careful in generalising this finding.

Remarkably, there was an interaction effect between the prevention protocol and the risk assessment method. Cau- tion is required in interpreting the results of the subgroups. If the data are split up into the Braden and NBE groups, the numbers of patients become too small. Therefore, we can

only discover tendencies. Patients identified as being in need of prevention based on the presence of NBE had a tendency to develop fewer pressure ulcers on an APAM (n = 8, 10.8%) than on a visco-elastic mattress in combination with turning every 4 hours (n = 16, 21.1%). However, this result was not statistically different. In the Braden group, the difference was not significant.

Considering the sacral pressure ulcers, we also observed an interaction effect between the prevention protocol and the risk assessment method. In the Braden group, a possible hypothesis for the slight tendency of more sacral pressure ulcers on an APAM is that the pressure on the sacrum cannot be completely relieved by an APAM. A constant low pressure remains on the sacrum. The literature provides evidence that constant low pressure is more damaging for the tissue than alternating pressure [27]. If there is a constant (low) pressure, repositioning on an APAM is required. Another hypothesis is that continued inflation and deflation of the cells of an APAM produces shearing forces. It is known that shearing forces increase the risk for developing pressure ulcers [13].

There were significantly less heel pressure ulcers in the APAM group (14.7%) than in the control group (45.7%). The percentage in the control group is consistent with other studies reporting anatomical locations [28, 29]. However, contrary to the present study, in those studies heels were not elevated from the mattress. The percentage in the APAM group was notably lower, but is still high considering that the heels were elevated from the mattress. One can question whether the heels were elevated from the mattress in the correct way. Some patients pushed away the cushion beneath their legs. Other patients turned up their legs and thus their heels were lying on the cush- ion. In the APAM group, when patients pushed away the cushion, their heels fell between the cells of the mattress and were pressure free.

For ethical reasons, the duration of sitting was not standardised. The sitting protocol was standardised. We found no significant difference in the analyses with or with- out mobile and chair-bound patients.

In conclusion, patients nursed on an APAM seemed to develop more severe pressure ulcers. Fewer patients developed heel pressure ulcers on an APAM. Patients identified as being in need of preventive measures based on the presence of NBE had a tendency to develop less pressure ulcers on an APAM than on a visco-elastic mattress in combination with 4-hourly turning. Patients identified as being in need of prevention based on the Braden Scale appeared to develop more sacral pressure ulcers on an APAM.

Key points • Fewer patients developed heel pressure ulcers on an

APAM. • Patients seemed to develop more severe pressure ulcers

on an APAM. • Patients identified as being in need of preventive measures

based on the presence of NBE had a tendency to develop

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Effectiveness of an alternating pressure air mattress

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less pressure ulcers on an APAM than on a visco-elastic mattress in combination with 4 hourly turning.

• Patients identified as being in need of prevention based on the Braden Scale appeared to develop more sacral pressure ulcers on an APAM than on a visco-elastic mat- tress in combination with 4 hourly turning.

Conflicts of interest declaration

There are no conflicts of interest.

Declaration of sources of funding

This study was supported by a grant from Ghent University and from Huntleigh Healthcare.

References 1. Panel for the Prediction and Prevention of Pressure Ulcers in

Adults. Pressure ulcers in adults : prediction and prevention. Clinical Practice Guideline no. 3. Public Health Service, Agency for Health Care Policy and Research. AHCPR Publi- cation no. 92–0047. Rockville, MD: US Department of Health and Human Services, 1992.

2. Defloor T. The effect of position and mattress on interface pressure. Appl Nurs Res 2000; 13: 2–11.

3. McLeod AG. Principles of alternating pressure surfaces. Adv Wound Care 1997; 10: 30–36.

4. Cullum N, Deeks J, Sheldon TA, Song F, Fletcher AW. Beds, mat- tresses and cushions for pressure sore prevention and treatment. The Cochrane Library 2003; (2): Oxford: Update Software Ltd.

5. Conine TA, Daechsel D, Lau MS. The role of alternating air and Silicore overlays in preventing decubitus ulcers. Int J Rehabil Res 1990; 13: 57–65.

6. Daechsel D, Conine TA. Special mattresses: effectiveness in preventing decubitus ulcers in chronic neurologic patients. Arch Phys Med Rehabil 1985; 66: 246–8.

7. Sideranko S, Quinn A, Burns K, Froman RD. Effects of position and mattress overlay on sacral and heel pressures in a clinical population. Res Nurs Health 1992; 15: 245–51.

8. Andersen KE, Jensen O, Kvorning SA et al. Decubitus prophy- laxis: a prospective trial of the efficiency of alternating-pres- sure-air-mattresses and water-mattresses. Acta Derm Venereol Stockh 1982; 63: 227–30.

9. Price P, Bale S, Newcombe R, Harding K. Challenging the pressure sore paradigm. J Wound Care 1999; 8: 187–90.

10. Bliss MR. Preventing pressure sores in elderly patients: a compari- son of seven mattress overlays. Age Ageing 1995; 24: 297–302.

11. Gebhardt KS, Bliss MR, Thomas J. Pressure-relieving sup- ports in an ICU. J Wound Care 1996; 5: 116–21.

12. Aranovitch SA, Wilber M, Slezak S, Martin T, Utter D. A comparative study of an alternating air mattress for the

prevention of pressure ulcers in surgical patients. Ostomy/ Wound Manage 1999; 45: 34–44.

13. Defloor T. The risk of pressure sores: a conceptual scheme. J Clin Nurs 1999; 8: 206–16.

14. Belgische richtlijnen voor decubituspreventie. [Belgian guide- lines for pressure ulcer prevention] (in Dutch). Academia Press, Ghent, Belgium, 2001.

15. CBO [Dutch Institute for Health Care Improvement]. Decu- bitus. Tweede herziening. [Second revision pressure ulcers] (in Dutch). CBO, Utrecht, The Netherlands, 2002.

16. European Pressure Ulcer Advisory Panel. Guidelines on treat- ment of pressure ulcers. EPUAP Review 1999; 1: 31–3.

17. Braden BJ, Bergstrom N. Predictive validity of the Braden Scale for pressure sore risk in a nursing home population. Res Nurs Health 1994; 17: 459–70.

18. Nixon J, McGough A. The prevention and treatment of pres- sure ulcers. In Morison M ed. Principles of patient assessment: screening for pressure ulcer and potential risk. London: Mosby, 2001: 55–74.

19. Schoonhoven L, Haalboom JRE, Bousema MT et al. Prospec- tive cohort study of routine use of risk assessment scales for prediction of pressure ulcers. BMJ 2002; 325: 797–800.

20. Vanderwee K, Grypdonck MH, Defloor T. Non-blanchable erythema as a predictor of pressure ulcer lesions: an alternative approach to risk assessment. EPUAP Rev 2003; 5: 22.

21. Tymec AC, Pieper B, Vollman K. A comparison of two pres- sure-relieving devices on the prevention of heel pressure ulcers. Adv Wound Care 1997; 10: 39–44.

22. Defloor T, Grypdonck MHF. Sitting posture and prevention of pressure ulcers. Appl Nurs Res 1999; 12: 136–42.

23. Derre B, Grypdonck M, Defloor T. The development of non- blanchable erythema in intensive care patients. STTI, editor. 26. 26–6–1999. London, 11th International Nursing Research Conference.

24. Halfens R, Bours G, Van Ast W. Relevance of the diagnosis ‘stage 1 pressure ulcer’: an empirical study of the clinical course of stage 1 ulcers in acute care and long-term care hospital populations. J Wound Care 2001; 10: 748–57.

25. SPSS Incorporated. SPSS for Windows, version 10.0. Chicago, IL: 1999.

26. Hofman A, Geelkerken RH, Wille J, Hamming JJ, Hermans J, Breslau PJ. Pressure sores and pressure-decreasing mattresses: controlled clinical trial. Lancet 1994; 343: 568–71.

27. Akbarzadeh MR. Behavior for relieving pressure. In Webster JG, ed. Prevention of pressure sores. Engineering and clinical aspects. Bristol: Adam Hilger, 1991, pp 175–90.

28. Bours G, Halfens R, Abu-Saad H, Grol R. Prevalence, prevention and treatment of pressure ulcers: Descriptive study in 89 institu- tions in the Netherlands. Res Nurs Health 2002; 25: 99–110.

29. Clark M, Bours G, Defloor T. Summary report on the preva- lence of pressure ulcers. EPUAP Rev 2002; 4: 49–57.

Received 18 August 2004; accepted in revised form 30 December 2004

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