Support surfaces for pressure ulcer prevention:

RESEARCH ARTICLE

Support surfaces for pressure ulcer

prevention: A network meta-analysis

Chunhu Shi1*, Jo C. Dumville1, Nicky Cullum1,2

1 Division of Nursing, Midwifery & Social Work, School of Health Sciences, Faculty of Biology, Medicine &

Health, University of Manchester, Manchester Academic Health Science Centre, Manchester, United

Kingdom, 2 Research and Innovation Division, Manchester University NHS Foundation Trust, Manchester

Academic Health Science Centre, Manchester, United Kingdom

* chunhu.shi@postgrad.manchester.ac.uk

Abstract

Background

Pressure ulcers are a prevalent and global issue and support surfaces are widely used for

preventing ulceration. However, the diversity of available support surfaces and the lack of

direct comparisons in RCTs make decision-making difficult.

Objectives

To determine, using network meta-analysis, the relative effects of different support surfaces

in reducing pressure ulcer incidence and comfort and to rank these support surfaces in

order of their effectiveness.

Methods

We conducted a systematic review, using a literature search up to November 2016, to iden-

tify randomised trials comparing support surfaces for pressure ulcer prevention. Two review-

ers independently performed study selection, risk of bias assessment and data extraction.

We grouped the support surfaces according to their characteristics and formed evidence

networks using these groups. We used network meta-analysis to estimate the relative

effects and effectiveness ranking of the groups for the outcomes of pressure ulcer incidence

and participant comfort. GRADE was used to assess the certainty of evidence.

Main results

We included 65 studies in the review. The network for assessing pressure ulcer incidence

comprised evidence of low or very low certainty for most network contrasts. There was mod-

erate-certainty evidence that powered active air surfaces and powered hybrid air surfaces

probably reduce pressure ulcer incidence compared with standard hospital surfaces (risk

ratios (RR) 0.42, 95% confidence intervals (CI) 0.29 to 0.63; 0.22, 0.07 to 0.66, respec-

tively). The network for comfort suggested that powered active air-surfaces are probably

slightly less comfortable than standard hospital mattresses (RR 0.80, 95% CI 0.69 to 0.94;

moderate-certainty evidence).

PLOS ONE | https://doi.org/10.1371/journal.pone.0192707 February 23, 2018 1 / 29

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OPENACCESS

Citation: Shi C, Dumville JC, Cullum N (2018)

Support surfaces for pressure ulcer prevention: A

network meta-analysis. PLoS ONE 13(2):

e0192707. https://doi.org/10.1371/journal.

pone.0192707

Editor: Yih-Kuen Jan, University of Illinois at

Urbana-Champaign, UNITED STATES

Received: September 27, 2017

Accepted: January 29, 2018

Published: February 23, 2018

Copyright: © 2018 Shi et al. This is an open access article distributed under the terms of the Creative

Commons Attribution License, which permits

unrestricted use, distribution, and reproduction in

any medium, provided the original author and

source are credited.

Data Availability Statement: All relevant data are

within the paper and its Supporting Information

files.

Funding: This work was supported by a President’s

Doctoral Scholarship to CS from the University of

Manchester. The funder had no role in study

design, data collection and analysis, decision to

publish, or preparation of the manuscript. We also

received some analytical advice from the Complex

Reviews Support Unit, which is funded by the

National Institute for Health Research (project

number 14/178/29).

 

 

Conclusions

This is the first network meta-analysis of the effects of support surfaces for pressure ulcer

prevention. Powered active air-surfaces probably reduce pressure ulcer incidence, but are

probably less comfortable than standard hospital surfaces. Most prevention evidence was

of low or very low certainty, and more research is required to reduce these uncertainties.

Introduction

Pressure ulcers are localised injuries to the skin and/or underlying tissue, which are also

known as pressure injuries, pressure sores, decubitus ulcers and bedsores [1]. Pressure ulcers

represent a serious heath burden with a point prevalence of approximately 3.1 per 10,000 in

the United Kingdom (UK) [2]. It has been estimated that the treatment of pressure ulcers costs

approximately 4% (between £1.4 and £2.1 billion) of the total health budget of the UK (1999/

2000 financial year) [3].

Pressure ulcers are caused by localised pressure and shear [1], thus intervention to alleviate

pressure and shear is an important part of pressure ulcer prevention. Support surfaces (e.g.

mattresses, overlays, integrated bed systems) are designed to work towards preventing pressure

ulcers primarily in this way [4]. Various types of support surfaces have been developed with

different mechanisms for pressure and shear relief including (1) redistributing the weight over

the maximum body surface area; (2) mechanically alternating the pressure beneath body to

reduce the duration of the applied pressure [5]; or (3) redistributing pressure by a combination

of the above, allowing health care professionals to change the mode according to a person’s

needs [6]. Support surfaces are made from a variety of construction materials (e.g. foam) and

have different functional features (e.g. low-air-loss) [4]. Identification of the optimum support

surface from the diverse options available requires evidence on their relative effectiveness in

terms of how well they prevent the incidence of new pressure ulcers [2].

Currently, seven systematic reviews containing meta-analyses have summarised rando-

mised controlled trial (RCT) and quasi-randomised trial evidence to inform choice of support

surface [7–13]. Of these reviews, one high-quality Cochrane review includes all studies covered

by the remaining six reviews and offers the most comprehensive summary of current evidence

[9]. However, all these reviews (including the Cochrane review [9]) use an outdated support

surface classification systems [5] now superseded by the recent internationally agreed NPUAP

Support Surface Standards Initiative (S3I) classification system [4]. Additionally, the reviews

all use pairwise meta-analysis to synthesise evidence for head-to-head comparisons of support

surfaces. There remains a lack of evidence on the relative effects of different support surfaces,

in part due to a lack of head-to-head RCT data across the plethora of treatment options

available.

To tackle this problem, an advanced meta-analysis technique, network meta-analysis, can

be employed. The approach can simultaneously compare multiple competing interventions in

a single statistical model whilst maintaining randomisation as with standard meta-analysis

[14–16]. The network meta-analysis has the following advantages. Firstly network meta-analy-

sis can produce “indirect evidence” for a potential comparison where a head-to-head compari-

son is unavailable. A network can be developed to link the direct evidence of, say, A vs. B and

B vs. C (i.e. evidence from studies with A vs. B and B vs. C as head-to-head comparisons), via a

common comparator (i.e. B in this example) to derive an indirect estimate of A vs. C. Sec-

ondly, both indirect and direct evidence can be used together which then improves the

Support surfaces for pressure ulcer prevention

PLOS ONE | https://doi.org/10.1371/journal.pone.0192707 February 23, 2018 2 / 29

Competing interests: The authors have declared

that no competing interests exist.

 

 

precision of effect estimates. Thirdly, effect estimates from network meta-analysis can be

linked to probabilistic modelling to allow the ranking of treatments based on which is likely to

be the most effective for the outcome of interest, which is likely to be the second best and so

on. This is a valuable approach for considering the results of the network across multiple inter-

ventions in a single measure [14–16].

The aim of this work was to synthesise the available evidence from RCTs in a network

meta-analysis to: (1) assess the relative effects of different classes of support surfaces for reduc-

ing pressure ulcer incidence in adults in any setting; (2) to assess the relative effects of different

classes of support surface in terms of reported comfort; and (3) to rank all classes of support

surface in order of effectiveness regarding pressure ulcer prevention.

Methods

This review was preceded by a protocol and registered prospectively in PROSPERO

(CRD42016042154). This report complies with the relevant PRISMA extension statement [17]

(see S1 File).

Search strategy

As the most comprehensive summary of available evidence in the topic of our review, the cur-

rent Cochrane review had identified and included 59 RCTs and quasi-randomised trials com-

paring support surfaces for pressure ulcer prevention, with a database search up to April 2015

[9].

We performed an update search of the following databases for the current Cochrane review:

the Cochrane Wounds Specialised Register (10 August 2016); the Cochrane Central Register

of Controlled Trials (CENTRAL) (2016, Issue 7); Ovid MEDLINE (1946 to 10 August 2016);

Ovid EMBASE (1974 to 10 August 2016); EBSCO CINAHL Plus (1937 to 10 August 2016).

Additionally, we searched the Chinese Biomedical Literature Database (1978 to 30 November

2016). There was no restriction on the basis of language or publication status (see S2 File for

Ovid MEDLINE Search Strategy).

We also searched other resources: ClinicalTrials.gov and WHO International Clinical Trials

Registry Platform (ICTRP) (24 August 2016), the Journal of Tissue Viability via hand-search-

ing (1991 to November 2016), and the reference lists of seven previously published systematic

reviews [7–13].

Eligibility criteria

We included published and unpublished RCTs, comparing pressure-redistribution support

surfaces—mattresses, overlays, and integrated bed systems—in adults at risk of pressure ulcer

development, in any setting. We excluded studies of seating and cushions, limb protectors,

turning beds, traditional Chinese medicine-related surfaces and home-made support surfaces.

Recent concern about the validity of RCTs from China led us to only consider those with

full descriptions of robust randomisation methods (e.g. random number tables) as eligible

[18, 19].

Our primary outcome was pressure ulcer incidence. We considered this outcome as either

the proportion of participants developing a new ulcer at the latest trial follow-up point (or the

pre-specified time point of primary focus if this was different to the longest follow-up point)

or time-to-pressure ulcer incidence. The secondary outcome was patient-reported comfort on

support surface (measured as the proportion of patients reporting comfort).

Support surfaces for pressure ulcer prevention

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Selection of studies

Two reviewers independently assessed the titles and abstracts of the search results for relevance

and then independently inspected the full text of all potentially eligible studies. Because the

non-Chinese database search was an updated search of the Cochrane review published by

McInnes and colleagues [9], all studies included by the Cochrane review were checked again

for relevance. Disagreements were resolved by discussion between the two reviewers and

involvement of a third reviewer if necessary.

Data extraction

Where eligible studies had been previously included in McInnes et al [9], one reviewer checked the original data extraction of these studies and extracted additional data where necessary, and

another reviewer checked all data. Two reviewers independently extracted data for new

included studies. Any disagreements were resolved by discussion and, if necessary, with the

involvement of a third reviewer. Where necessary, the authors of included studies were con-

tacted to collect and/or clarify data.

The following data were extracted using a pre-prepared data extraction form: basic charac-

teristics of studies (e.g. country, setting, and funding sources); characteristics of participants

(including eligibility criteria, average age, proportions of participants by gender, and partici-

pants’ baseline skin status); description of support surfaces and details on any co-interven-

tions; number randomised, follow-up durations; drop-outs; primary and secondary outcome

data.

In order to assign support surfaces to intervention groups, we extracted full descriptions

from included studies where possible. However, when necessary we supplemented the infor-

mation provided with that from external sources such as other publications about the same

support surface, manufacturers’ and/or product websites and expert clinical opinion [20].

Classification of interventions. Support surfaces in included studies were classified using

the NPUAP system [4] and assigned to one of 14 intervention groups [21] (see S3 File for the

detailed steps and Table 1 for the 14 intervention groups).

Risk of bias assessment

We used Cochrane’s Risk of Bias tool to assess risk of bias of each included study [22]. For new

included studies, two reviewers independently assessed domain-specific risk of bias [22]. For

studies included by McInnes and colleagues [9], previous judgements were checked by two

reviewers independently and, where required, updated. Any discrepancy between two review-

ers was resolved by discussion and a third reviewer where necessary.

We then followed GRADE principles to summarise the overall risk of bias across domains

for each included study [23]. After this, we applied the approach proposed by Salanti and col-

leagues [24] to judge the overall risk of bias (referred to hereon as “study limitations”) for

direct evidence (i.e. pairwise meta-analysis), network contrasts, and the entire network. Three

categories were used to qualitatively rate study limitations: no serious limitations; serious limi-

tations; and very serious limitation.

Data synthesis and analyses

We conducted all meta-analyses based on a frequentist framework with a random effects

model [25]. All estimates are presented as risk ratios (RR) with 95% confidence intervals (CIs).

When presenting summaries of findings, we also calculated the absolute risk of an event for a

specific intervention group compared with that for a standard hospital surface. The baseline

Support surfaces for pressure ulcer prevention

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risk used was the outcome on standard hospital surfaces (the median risk across studies that

provided data for the outcome).

We performed pairwise meta-analyses in RevMan, calculated I-squared (I2) measures and

visually inspected the forest plots to assess statistical heterogeneity [26]. We then conducted

network meta-analysis in STATA1 (StataCorp. 2013) using published network commands

Table 1. 14 intervention groups, explanations and selected examples from included studies.

Intervention groups Reviewers’ explanations Selected examples (with support surface brands if possible)

Powered/non-powered reactive

air surfaces

A group of support surfaces constructed of air-cells, which

redistribute body weight over a maximum surface area (i.e. has

reactive pressure redistribution mode), with or without the

requirement for electrical power

Static air mattress overlay, dry flotation mattress (e.g., Roho,

Sofflex), static air mattress (e.g., EHOB), and static mode of Duo 2

mattress

Powered/non-powered reactive

low-air-loss air surfaces

A group of support surfaces made of air-cells, which have reactive

pressure redistribution modes and a low-air-loss function, with

or without the requirement for electrical power

Low-air-loss Hydrotherapy

Powered reactive air-fluidised

surfaces

A group of support surfaces made of air-cells, which have reactive

pressure redistribution modes and an air-fluidised function, with

the requirement for electrical power

Air-fluidised bed (e.g., Clinitron)

Non-powered reactive foam

surfaces

A group of support surfaces made of foam materials, which have

a reactive pressure redistribution function, without the

requirement for electrical power

Convoluted foam overlay (or pad), elastic foam overlay (e.g.,

Aiartex, microfluid static overlay), polyether foam pad, foam

mattress replacement (e.g. MAXIFLOAT), solid foam overlay,

viscoelastic foam mattress/overlay (e.g., Tempur, CONFOR-Med,

Akton, Thermo)

Non-powered reactive fibre

surfaces

A group of support surfaces made of fibre materials, which have a

reactive pressure redistribution function, without the

requirement for electrical power

Silicore (e.g., Spenco) overlay/pad

Non-powered reactive gel

surfaces

A group of support surfaces made of gel materials, which have a

reactive pressure redistribution function, without the

requirement for electrical power

Gel mattress, gel pad used in operating theatre

Non-powered reactive

sheepskin surfaces

A group of support surfaces made of sheepskin, which have a

reactive pressure redistribution function, without the

requirement for electrical power

Australian Medical Sheepskins overlay

Non-powered reactive water

surfaces

A group of support surfaces based on water, which has the

capability of a reactive pressure redistribution function, without

the requirement for electrical power

Water mattress

Powered active air surfaces A group of support surfaces made of air-cells, which

mechanically alternate the pressure beneath the body to reduce

the duration of the applied pressure (mainly via inflating and

deflating to alternately change the contact area between support

surfaces and the body) (i.e. alternating pressure (or active)

mode), with the requirement for electrical power

Alternating pressure-relieving air mattress (e.g., Nimbus II,

Cairwave, Airwave, MicroPulse), large-celled ripple

Powered active air surfaces and

non-powered reactive foam

surfaces

A group of support surfaces which use powered active air surfaces

and non-powered reactive foam surfaces in combination

Alternating pressure-relieving air mattress in combination with

viscoelastic foam mattress/overlay (e.g., Nimbus plus Tempur)

Powered active low-air-loss air

surfaces

A group of support surfaces made of air-cells, which have the

capability of alternating pressure redistribution as well as low-air-

loss for drying local skin, with the requirement for electrical

power

Alternating pressure low-air-loss air mattress

Powered hybrid system air

surfaces

A group of support surfaces made of air-cells, which offer both

reactive and active pressure redistribution modes, with the

requirement for electrical power

Foam mattress with dynamic and static modes (e.g. Softform

Premier Active)

Powered hybrid system low-

air-loss air surfaces

A group of support surfaces made of air-cells, which offer both

reactive and active pressure redistribution modes as well as a low-

air-loss function, with the requirement for electrical power

Stand-alone bed unit with alternating pressure, static modes and

low air-loss (e.g., TheraPulse)

Standard hospital surfaces A group of support surfaces made of any materials, used as usual

in a hospital and without reactive nor active pressure

redistribution capabilities, nor any other functions (e.g. low-air-

loss, or air-fluidised).

Standard hospital (foam) mattress, NHS Contract hospital

mattress, standard operating theatre surface configuration,

standard bed unit and usual care

https://doi.org/10.1371/journal.pone.0192707.t001

Support surfaces for pressure ulcer prevention

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and network graph packages [27, 28] (see S4 File for STATA commands used in the review). A

consistency model was fitted to estimate relative effects [29]. Following this, we calculated the

relative rankings of intervention groups and presented the surface under the cumulative rank-

ing curve (SUCRA) percentages [27]. For any outcome, we performed network meta-analysis

only if intervention groups could be connected to form a network; however, we did not

exclude comparisons of support surfaces assigned to the same group from the overall system-

atic review. The full dataset is available on request.

We assessed the transitivity assumption for each network by comparing the similarities of

study-level characteristics across direct comparisons within the network [30]. When data were

insufficient for this assessment, we assumed that the transitivity assumption was met. Inconsis-

tency between direct and indirect evidence was examined globally by running the design-by-

treatment interaction model and locally by using the node-splitting method and inconsistency

plot test [28, 31–33]. We also explored the sensitivity of the global inconsistency finding to

alternative modelling approaches by running a post hoc sensitivity analysis using the model of

Lu and Ades [34]. It is worth noting that because the model of Lu and Ades [34] depends on

the ordering of treatments in the presence of multi-arm studies [28] the design-by-treatment

interaction model was used in the main analysis. We then evaluated the common network het-

erogeneity using the tau-squared (tau2) and the I2 measure and the 95% CIs of I2, and decom-

posed the common network heterogeneity to inconsistency and within-study heterogeneity in

R to locate the source of heterogeneity [35]. The heterogeneity was considered as low, moder-

ate, or high if I2 = 25%, 50%, or 75%, respectively [36].

When important inconsistency and/or heterogeneity occurred, we followed steps proposed

by Cipriani and colleagues [37] to investigate further. Of these steps, we performed pre-speci-

fied subgroup analyses for funding sources [38] and risk of bias [39]; as well as four exploratory

sub-group analyses: setting, considering operating theatre as setting or not, baseline skin sta-

tus, and follow-up duration. Additionally, we performed one sensitivity analysis to assess the

impact of missing data (i.e. a complete case analysis for the main analysis, followed by a

repeated analysis with missing data added to the denominator but not the numerator) and

another one for the impact of unpublished studies by removing them from the analysis.

Assessing the certainty of evidence

We assessed the potential for publication bias by considering the completeness of the literature