Systemic review article

How to cite this article

Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM. Support surfaces for intraoperative

pressure injury prevention: systematic review with meta-analysis. Rev. Latino-Am. Enfermagem. 2021;29:e3493.

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. DOI: http://dx.doi.org/10.1590/1518-8345.5279.3493

* Paper extracted from doctoral dissertation “Support surfaces
for prevention for pressure ulcer in the intraoperative
period: systematic review with meta-analysis”, presented
to Universidade de São Paulo, Escola de Enfermagem de
Ribeirão Preto, PAHO/WHO Collaborating Centre for Nursing
Research Development, Ribeirão Preto, SP, Brazil.

1 Universidade de Uberaba, Ciências da Saúde, Uberaba,
MG, Brazil.

2 Universidade de São Paulo, Escola de Enfermagem de
Ribeirão Preto, PAHO/WHO Collaborating Centre for Nursing
Research Development, Ribeirão Preto, SP, Brazil.

3 Scholarship holder at the Conselho Nacional de
Desenvolvimento Científico e Tecnológico/Ministério da
Ciência, Tecnologia e Inovações, Brazil.

Support surfaces for intraoperative pressure injury prevention:
systematic review with meta-analysis*

Objective: to evaluate evidence on effectiveness support

surfaces for pressure injury prevention in the intraoperative

period. Method: systematic review. The search for primary

studies was conducted in seven databases. The sample

consisted of 10 studies. The synthesis of the results was carried

out descriptively and through meta-analysis. Results: when

comparing low-tech support surfaces with regular care (standard

surgical table mattress), the meta-analysis showed that there is

no statistically significant difference between the investigated

interventions (Relative Risk = 0.88; 95%CI: 0.30-2.39). The

Higgins inconsistency test indicated considerable heterogeneity

between studies (I2 = 83%). The assessment of the certainty

of the evidence was very low. When comparing high-tech and

low-tech support surfaces, the meta-analysis showed that there

is a statistically significant difference between the interventions

studied, with high-tech being the most effective (Relative Risk

= 0.17; 95%CI: 0.05-0.53). Heterogeneity can be classified

as not important (I2 = 0%). The assessment of certainty of

evidence was moderate. Conclusion: the use of high-tech

support surfaces is an effective measure to prevent pressure

injuries in the intraoperative period.

Descriptors: Perioperative Nursing; Pressure Ulcer; Systematic

Review; Meta-Analysis; Intraoperative Period; Equipment and

Supplies.

Review Article

Rev. Latino-Am. Enfermagem
2021;29:e3493
DOI: 10.1590/1518-8345.5279.3493
www.eerp.usp.br/rlae

Carolina Beatriz Cunha Prado1

https://orcid.org/0000-0002-4570-9502

Elaine Alves Silva Machado1

https://orcid.org/0000-0002-3683-6438

Karina Dal Sasso Mendes2

https://orcid.org/0000-0003-3349-2075

Renata Cristina de Campos Pereira Silveira2

https://orcid.org/0000-0002-2883-3640

Cristina Maria Galvão2,3

https://orcid.org/0000-0002-4141-7107

www.eerp.usp.br/rlae

2 Rev Latino-Am. Enfermagem 2021;29:e3493.

Introduction

Pressure injury (PI) is an adverse event that can

affect the surgical patient. In recently published clinical

guidelines, information based on research results

indicated that the incidence of this type of injury, directly

attributable to the surgical anesthetic procedure, can

range from 4% to 45%(1). This variability of data must

be interpreted with caution, since in the intraoperative

period skin changes due to the appearance of PI may

take a while to manifest, several hours or even three to

five days after surgery. This condition can generate an

underestimated number of this type of injury resulting

from the surgical anesthetic procedure; in addition, it

is commonly attributed to the postoperative period or

confused with burns(1).

In the intraoperative period, the appearance of PI

is related to different factors, which can be classified as

intrinsic to the patient (for example, age, Body Mass Index

and presence of chronic disease), extrinsic (for example,

exposure to pressure, especially in bone prominences,

friction, shear and altered microclimate) and related to

the surgical anesthetic procedure (duration of the surgical

anesthetic procedure, type of surgical position, among

others)(2-4).

In the literature there is evidence of the importance

of using support surfaces for the prevention of PI in the

intraoperative period. These devices can be mattresses,

overlays or specific pads for different parts of the human

body, and they can be made of foam, gel, viscoelastic

polymer, air or fluids(1,5-6). Support surfaces can be

classified into high tech and low tech. The first one is

dynamic, capable of changing the pressure distribution

with or without load applied and powered by an energy

source (for example: alternating pressure overlay). On

the other hand, the low-tech surface is not powered

by electricity and adapts to the shape of the body,

distributing body weight over a large area (for example:

dry viscoelastic overlay)(7). On the other hand, there are

knowledge gaps, which are the most effective support

surfaces for use in the operating room(7-8).

The perioperative nurse has a fundamental role in the

assessment of the patient before the surgical anesthetic

procedure and in the identification of predisposing factors

for the occurrence of skin lesions, including PI. In the

intraoperative period, the planning and implementation of

care for the prevention of PI are crucial for the reduction

of complications associated with this type of injury, such

as: intense pain in the postoperative period, not related

to the surgical site; patient dissatisfaction; the extension

of the length of stay; the increase in the expenses of the

public/private health system(9).

This systematic review was conducted in an attempt

to contribute to the advancement of knowledge about the

problem in question. In addition to providing support for

nurses’ decision-making in clinical practice, with a view

to increasing the quality of care provided and reducing

costs, mainly related to the treatment of PI and the use

of appropriate technology in the operating room. Thus,

the delimited objective was to evaluate the evidence

on effectiveness support surfaces for the prevention of

pressure injuries in the intraoperative period.

Method

Type of study

This is a systematic review of health interventions

and was conducted based on the recommendations of the

Cochrane Collaboration. The following steps were taken:

1) elaboration and registration of the review protocol;

2) delimitation of the review question; 3) definition of

eligibility criteria; 4) search and selection of studies;

5) data collection; 6) synthesis and presentation of

the results of the systematic review(10). The Preferred

Reporting Items for Systematic Review and Meta-Analyses

(PRISMA) checklist guidelines were also adopted to report

the systematic review(11).

The review protocol was registered in the International

Prospective Register of Systematic Reviews (PROSPERO).

The registration number is CRD42019131271 and the

protocol can be accessed at the website (https://www.

crd.york.ac.uk/prospero/display_record.php).

Setting

The systematic review was conducted in the city of

Ribeirão Preto, state of São Paulo, Brazil.

Period

The systematic review took place from January to

November 2020.

Population

The delimited review question was: “what are the

effective support surfaces for the prevention of pressure

injuries in patients during the intraoperative period?”. The

question followed the components of the acronym PICOT

(population, intervention, comparison, outcome and time),

being P = surgical patient; I = tested support surface; C

= standard care (non-use of support surface) or support

surface different from the one tested; O = pressure injury

prevention; T = intraoperative period.

www.eerp.usp.br/rlae

3Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM.

Selection criteria

In the systematic review, primary studies that met

the components of the PICOT strategy were included, and

those in which the population consisted of patients under

18 years old or volunteers were excluded. Systematic

reviews of the effectiveness of health interventions

advocated by the Cochrane Collaboration traditionally

focus on the inclusion of randomized controlled trials.

However, this organization also discusses the inclusion,

in this type of review, of non-randomized studies of

interventions(10). Given the above and the diversity of

non-randomized study designs, the reviewers delimited

the inclusion of randomized controlled trials and non-

randomized studies, whose authors investigated the

effectiveness of support surfaces in preventing pressure

injuries in the intraoperative period. With regard to non-

randomized studies, studies that in the design presented

at least two comparative groups (for example, a control

group and an intervention group) were selected. It is

also noteworthy that for the selection of primary studies,

limitations of language or period of publication were not

established.

Sample definition

The databases selected for the search of primary

studies were PubMed, Cumulative Index to Nursing and

Allied Health Literature (CINAHL), Cochrane Central

Register of Controlled Trials (CENTRAL), EMBASE,

Scopus, Web of Science, and Latin American and Latin

American Literature Caribbean in Health Sciences

(LILACS).

Before performing the final searches of the

primary studies in the selected databases, several

combinations were performed using the controlled

descriptors, keywords and the Boolean operators AND

and OR, this was done in order to identify the largest

possible number of publications. For this step, the

combinations adopted the five components of the PICOT

strategy. However, it was observed that the removal of

P and C elements allowed the increase of the search

amplitude. Thus, the combination I AND O AND T was

used, and in four databases, PubMed, CENTRAL, Web

of Science and Scopus, the controlled descriptors were

delimited from the Medical Subject Headings (MeSH)

and the search strategies adopted were: I – “Equipment

and Supplies”[Mesh] OR “Supplies and Equipment”

OR “Apparatus and Instruments” OR “Instruments

and Apparatus” OR “Supplies” OR “Inventories” OR

“Inventory” OR “Medical Devices” OR “Medical Device”

OR “Device, Medical” OR “Devices, Medical” OR “Devices”

OR “Device” OR “Equipment” OR “support surface” OR

“foam mattress” OR “gel mattress” OR “visco-elastic

polyether foam mattress” OR “visco-elastic polyurethane

mattress” OR “polymers” OR “mattress” OR “foam”

OR “viscoelastic” OR “pillows polyurethane foam” OR

“rubber foam” OR “pillows” OR “cushion” OR “overlay”

OR “pad” OR “Dry viscoelastic Polymer”; O – “Pressure

Ulcer”[Mesh] OR “Pressure Ulcers” OR “Ulcer, Pressure”

OR “Ulcers, Pressure” OR “Bedsore” OR “Bedsores” OR

“Pressure Sore” OR “Pressure Sores” OR “Sore, Pressure”

OR “Sores, Pressure” OR “Bed Sores” OR “Bed Sore” OR

“Sore, Bed” OR “Sores, Bed” OR “Decubitus Ulcer” OR

“Decubitus Ulcers” OR “Ulcer, Decubitus” OR “Ulcers,

Decubitus” OR “Interface pressure” OR “Pressure ulcer

Prevention and control” OR “intraoperative pressure

injuries” OR “intraoperatively acquired pressure ulcer”

OR “Wounds and Injuries”[Mesh] and T – “Intraoperative

Period”[Mesh] OR “Intraoperative Periods” OR “Period,

Intraoperative” OR “Periods, Intraoperative”. In the other

databases, CINAHL, EMBASE and LILACS, the search

strategies used were similar, however the controlled

descriptors used were in accordance with the base

vocabulary, namely: CINAHL Headings, Emtree and

Descriptors in Health Sciences (DeCS).

At the end of the search for primary studies in all

selected databases, the results were exported to EndNote

Basic (desktop version) for the removal of duplicates(12).

Then, all citations from the reference manager were

imported into the Rayyan technology platform of the Qatar

Computing Research Institute (QCRI), specifically aimed

at the study selection phase among reviewers. Thus,

allowing the blinding between these and the monitoring

of the selection process by the main researcher. This

platform can be accessed through an electronic address

(https://rayyan.qcri.org/welcome) or as an application

for smartphones(13).

Titles and abstracts of primary studies identified

in the databases and imported from EndNote Basic

to the Rayyan platform were independently assessed

by two reviewers to determine which studies met the

aforementioned eligibility criteria. The reading of the

primary studies, in full, was also carried out independently

by two reviewers. In those cases where there was

disagreement between reviewers, a third reviewer was

consulted to solve the question.

The search and selection of primary studies that were

included in the review sample took place from February to

April 2020. Through a manual search, the main reviewer

tried to identify, in the reference list of each study included

in the review, other studies that could answer the guiding

question. However, no study was selected.

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4 Rev Latino-Am. Enfermagem 2021;29:e3493.

Data collection

A standard form was developed to collect data from

the studies included in the systematic review. The script

items were: authors; study title; year of publication;

journal name; goal; sample; inclusion and exclusion

criteria for the investigated population; randomization;

blinding; type of anesthesia and duration; type of

surgery and duration; intervention/experimental group;

group control; number of patients who had pressure

injury at the end of the study; statistical analysis; main

results; conclusion. Data collection was again carried

out by two reviewers, independently, in May and June

2020. To solve items and/or information that presented

divergences, meetings were scheduled between

reviewers for discussion and resolution of divergent

aspects until consensus.

Data analysis

To analyze the risk of bias of the randomized

controlled trials included in the review (n=6), the

free tool named Revised Cochrane risk-of-bias tool

for randomized trials (RoB 2), which is proposed by

the Cochrane Collaboration(10) was adopted. This tool

has five domains, namely: bias resulting from the

randomization process; bias due to deviations from

intended interventions; bias from missing outcome data;

bias from the measurement of the outcome; bias from

the selection of the reported result. Such analysis was

performed by two reviewers, independently. Through

meetings, the results of each evaluated study and the

doubts were discussed until the reviewers reached

consensus.

To assess the methodological quality of the non-

randomized studies (n=4), the quasi-experimental study

tool proposed by the Joanna Briggs Institute (JBI) was

used. The tool is called JBI Critical Appraisal Checklist

for Quasi-Experimental Studies, and is composed of

nine questions. For each question, the reviewer answers

yes, no, unclear or not applicable. The questions are

aimed at assessing the study’s internal validity and

risk of bias (selection of participants, conduction and

analysis of results)(14). In this analysis, two reviewers

also independently assessed the four studies. Then, a

meeting was held to discuss doubts and final evaluation

of the research. The adopted tool does not have a scoring

system for the general evaluation of the study.

The summary of the review results was carried

out in descriptive form and through meta-analysis.

To perform the meta-analysis, randomized controlled

trials were grouped according to the support surfaces

investigated by the researchers. The delimited meta-

analysis analysis model was the random effect, using

the software Review Manager (RevMan) version 5.3 of

the Cochrane Collaboration.

The assessment of the certainty of the evidence

was performed using the Grading of Recommendations

Assessment, Development and Evaluation (GRADE). This

assessment is performed for each outcome analyzed. In

this review, the outcome is the development of pressure

injury related to the use of support surfaces using the

evidence available in the literature. The certainty of the

evidence can be assessed as high (strong confidence

that the true effect is close to that estimated), moderate

(moderate confidence in the estimated effect), low (limited

confidence in the effect estimate) and very low (very

limited confidence in the estimate of the effect)(15). The

assessment of the certainty of the evidence was performed

using the GRADEpro software (https://www.gradepro.org).

Results

In Figure 1, the detailed flowchart of the selection

process of the primary studies included in the systematic

review is presented. Thus, the review sample consisted

of 10 studies, with six randomized controlled trials and

four non-randomized studies.

In Figure 2, the descriptive synthesis of the primary

studies was presented. The following data were indicated:

authors and year of publication of the research; sample;

support surfaces tested in the intervention and control

groups; number of PI in each group; the incidences of

the analyzed outcome. Missing data were not described

by the authors of the included studies.

www.eerp.usp.br/rlae

5Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM.

Source: Moher, et al.(11)

*CENTRAL = Cochrane Central Register of Controlled Trials; †LILACS = Latin American and Caribbean Literature in Health Sciences; ‡CINAHL = Cumulative
Index to Nursing and Allied Health Literature; §PI = Pressure injury

Figure 1 – Flowchart of the selection process of primary studies included in the systematic review adapted from Preferred

Reporting Items for Systematic Review and Meta-Analyses (PRISMA). Ribeirão Preto, SP, Brazil, 2020

Study Sample IG*/support surface/Technology type CG†/support surface/technology type PI‡

IG*
PI‡

CG†

Nixon, et al.
(1998)(16) n=416 n=205/dry viscoelastic polymer pad/

low tech
n=211/standard surgical table mattress/regular
care

22
I§=11%

(22/205)

43
I§=20%
(43/211)

Aronovitch, et
al. (1999)(17) n=217 n=112/alternating pressure system/

high technology n=105/dry viscoelastic polymer overlay/low tech 0
7

I§=8.75%
(7/105)

Schultz, et al.
(1999)(18) n=413 n=206/ special foam cover for

operating room/low tech mattress
n=207/gel pads, egg box foam mattress and
“foam donuts”/low tech

55
I§=26.6%
(55/206)

34
I§=16.4%
(34/207)

Russell;
Lichtenstein
(2000)(19)

n=198 n=98/multi-cell pulsatile dynamic
mattress system/high-tech n=100/dry viscoelastic polymer pad/low tech

2
I§=2.2%
(2/98)

7
I§=7.7%
(7/100)

Feuchtinger, et
al. (2006)(20)

n=175
I§=14.3%

n=85/4 cm thermoactivated
viscoelastic foam cover/low tech

n=90/standard surgical table mattress/regular
care

15
I§=17.6%
(15/85)

10
I§=11.1%
(10/90)

(continues on the next page…)

www.eerp.usp.br/rlae

6 Rev Latino-Am. Enfermagem 2021;29:e3493.

Study Sample IG*/support surface/Technology type CG†/support surface/technology type PI‡

IG*
PI‡

CG†

Huang, et al.
(2018)(21)

n=120

I§=8.3%

n=60/alternating air cushion positioned
under the head/high tech n=60/gel pad positioned under the head/low tech

1
I§=1.7%
(1/60)

9
I§=15%
(9/60)

Non-
randomized
study

Hoshowsky;
Schramm
(1994)(22)

n=505

n=85/PI‡

I§=16.8%

Group 1: SFM|| versus FGM¶ (n=91)
Group 2: VEO** above de SFM|| versus
FGM (n=92)
Group 3: SFM|| versus VEO** above
FGM (n=62)
Group 4: VEO** above SFM|| versus
VEO** above FGM¶ (n=113)
Group 5- SFM|| versus VEO** above
SFM (n = 73)
Group 6- FGM¶ versus VEO** above
FGM¶ (n = 74)

_ _ _

Wu, et al.
(2011)(23)

n=30

I§=7.5%
n=30/high density foam pad/low tech n=30/viscoelastic polymer pad/low tech

6
I§=10%
(6/30)

2
I§=5%
(2/30)

Joseph, et al.
(2019)(24) n=392 n=100/low profile alternating pressure

overlay/high tech
n=292/standard surgical table mattress/regular
care

0
I§=0%
(0/100)

18
I§=6%

(18/292)

Ezeamuzie, et
al. (2019)(25) n=212 n=104/low profile alternating pressure

overlay/high tech n=108/standard gel polymer mattress/low-tech
1

I§=0.96%
(1/104)

7
I§=6.5%
(7/108)

*IG = Intervention group; †CG = Control group; ‡PI = Pressure injury; §I = Incidence; ||SFM = Standard surgical table mattress (regular care); ¶FGM = Two-
inch thick foam and surgical table gel mattress coated with nylon fabric (low tech); **VEO = Dry viscoelastic polymer overlay (low tech)

Figure 2 – Characterization of primary studies included in the systematic review. Ribeirão Preto, SP, Brazil, 2020

Figure 3 shows the result of the risk of bias assessment using the RoB 2 tool, which was presented for each of

the six randomized controlled trials included in the systematic review.

Study R
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at

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pr
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s

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tio

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fr

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ea

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rt
ed

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t

O
ve

ra
ll

B
ia

s

Nixon, et al. (1998)(16) Low risk

Aronovitch, et al. (1999)(17) Some concerns

Schultz, et al. (1999)(18) High risk

Russell; Lichtenstein (2000)(19)

Feuchtinger, et al. (2006)(20)

Huang, et al. (2018)(21)

+

+

+

+

+

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+

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+

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Figure 3 – Risk of bias assessment of randomized controlled trials in each domain of the Revised Cochrane risk-of-bias

tool for randomized trials (RoB 2). Ribeirão Preto, SP, Brazil, 2020

www.eerp.usp.br/rlae

7Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM.

Of the six randomized controlled trials, 66.7% (n=4)

were considered to be at low risk of bias and 33.3%

(n=2) were considered to be at high risk of bias. In two

studies(17,19) the bias domain in the measurement of results

was evaluated as being of high risk, since there was no

information about blinding of the result evaluators, that

is, the evaluator could know which was the participant’s

group and perform less rigorous evaluation for patients

in the experimental group regarding the outcome, in

this case, the development of PI. In one study(19) the

bias domain in the selection of reported outcome was

also assessed as high risk, that is, researchers reported

outcome measures selectively favorable to the intervention

of the experimental group.

The assessment of the methodological quality of the

non-randomized studies (n=4) was performed using the

JBI Critical Appraisal Checklist for Quasi-Experimental

Studies, as already mentioned, this tool does not have

a scoring system. Thus, of the nine questions that make

up the checklist, in two studies(24-25), eight questions

received the answer “yes” in the assessment carried

out by the reviewers; in one study(22), seven questions

received “yes”; and in the other research(23), five

questions received “yes”, and in the evaluation, three

questions received the answer “not applicable”, since

the questions were related to follow-up and comparison

between the control and experimental groups. In this

study, the support surfaces were tested on the same

patient, and the high-density foam pad was tested under

the right chest and the right iliac crest (experimental

intervention), and the viscoelastic polymer pad was

tested under the left chest and the left iliac crest (control

intervention).

In the meta-analysis, only randomized controlled

trials with similar characteristics regarding the surfaces

tested in the intervention and control groups were

included. As already mentioned, the outcome considered

to assess the effectiveness of the support surfaces was

the development of pressure injury in the intervention

and control groups. In Figure 4, two meta-analyses were

presented. The first considers clinical trials in which the

authors tested low-tech support surfaces in comparison

with usual care (standard surgical table mattress) (Figure

4 A.1). In the second meta-analysis, the clinical trials in

which researchers investigated high-tech support surfaces

compared to low-tech support surfaces are considered

(Figure 4 A.2). The Relative Risk (RR) was indicated in

the last column of the forest plots.

Figure 4 – Forest plots from meta-analyses addressing pressure injury prevention interventions. Ribeirão Preto, SP,

Brazil, 2020

In Figure 4 A.1, when comparing low-tech support

surfaces with usual care (standard surgical table

mattress), the interpretation of the meta-analysis

indicates that there is no statistically significant

difference between the investigated interventions (RR

= 0, 88; 95%CI: 0.30-2.39). On the other hand, in

Figure 4 A.2, when comparing high-tech and low-tech

support surfaces, the interpretation of the meta-analysis

shows that there is a statistically significant difference

between the investigated interventions, with the high-

tech ones being the most effective (RR = 0.17; 95%CI:

0.05-0.53).

(A.1) Low Tech versus Usual Care (Standard Surgical Table Mattress)

(A.2) High Tech versus Low Tech

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8 Rev Latino-Am. Enfermagem 2021;29:e3493.

In Figure 4 A.1, the Higgins inconsistency statistical

test (I2) indicated considerable heterogeneity between

studies (I2 = 83%). On the other hand, on Figure 4

(A.2), heterogeneity can be classified as unimportant

(I2 = 0%).

In Table 1, the assessment of certainty of evidence

by the GRADE system was presented. As explained above,

this assessment is performed for each outcome, in the

case of this review, the development of pressure injury.

Thus, when comparing low-tech support surfaces with

usual care, the certainty of the evidence was very low

(very limited confidence in the estimation of the effect),

as it presented very serious inconsistency, that is,

considerable heterogeneity (I2 = 83%). Furthermore, the

imprecision was also rated as very severe due to variation

in the effect estimate. When comparing high-tech and low-

tech support surfaces, the certainty of the evidence was

moderate (moderate confidence in the estimated effect),

since two randomized controlled trials were evaluated at

high risk of bias.

Table 1 – Synthesis of the assessment of the certainty of evidence, according to the Grading of Recommendations

Assessment, Development and Evaluation (GRADE). Ribeirão Preto, SP, Brazil, 2020

Certainty of evidence Number of
patients Effect

Number
of study

Type of
study

Risk of
bias Inconsistency Indirect

evidence Imprecision Other
considerations I* C† Relative

(95% CI‡)

Absolute
(95%
CI‡)

Certainty

Incidence of Pressure Injury/Low Technology versus Standard Surgical Table Mattress

2 RCT§ not
serious very serious|| not

serious
very

serious¶| none 37/290
(12.8%)

53/301
(17.6%)

not
estimable

20 plus
per

1,000
(from
140

minus
to 180
plus)

⃝⃝⃝
Very low

Incidence of Pressure Injury/High Tech versus Low Tech

3 RCT§ serious** not serious not
serious not serious none 3/270

(1.1%)
23/265
(8.7%)

RR†† =
0.17

(0.05 to
0.53)

72 minus
per

1,000
(from 82
minus
to 41

minus)

⃝
Moderate

*I = Intervention; †C = Control; ‡CI = Confidence interval; §RCT = Randomized controlled trial; ||The justification for the assessment is that the Higgins
inconsistency test (I2=83%) indicated considerable heterogeneity between studies; ¶|The justification for the assessment is that the effect estimate varies
greatly; **The justification for the assessment is that two randomized controlled trials were considered to be at high risk of bias; ††RR = Relative risk

Discussion

To make the discussion of the evidenced results

easier, three categories were defined (the first one

comparing low-tech support surfaces with regular care,

that is, standard surgical table mattress), in addition,

two randomized controlled trials were grouped(16,20). In a

study(20) the results led to the interruption of the research,

since the patients in the intervention group (overlay of

thermoactive viscoelastic foam of 4 cm) had a higher

number of PI, although the difference between the groups

was not statistically significant. In another study(16), the

results showed that the use of a dry viscoelastic polymer

pad was more effective in preventing PI compared to

regular care (OR=0.46; 95%CI: 0.26-0.82; p=0.01).

In a quasi-experimental study carried out in Brazil,

the authors evaluated the interface pressure of support

surfaces in bony prominences, at specific points (occipital,

subscapular, sacral and calcaneal regions) in 20 healthy

volunteers in supine position on a surgical table. Seven

different combinations were evaluated, namely: standard

surgical table mattress without overlaying; the viscoelastic

polymer overlay; three overlays of 5 cm thick sealed foam

at densities 28, 33 and 45 kg/m3; two overlays of soft

foam 5 cm thick and densities 28 and 18 kg/m3. The mean

interface pressure of the viscoelastic polymer overlay was

higher compared to the other surfaces tested, including

the standard surgical table mattress (p<0.001)(5).

The second category (high-tech support surfaces

versus low-tech surfaces) included three randomized

controlled trials(17,19,21) and two non-randomized

studies(24-25). In all studies, the high-tech surfaces

tested were alternating pressure devices from different

manufacturers. In two randomized controlled trials(17,19),

the MicroPulse® System alternating air overlay

(MicroPulse, Inc., Portage, Michigan, USA) was tested.

www.eerp.usp.br/rlae

9Prado CBC, Machado EAS, Mendes KDS, Silveira RCCP, Galvão CM.

In non-randomized studies(24-25), low-profile alternating

pressure overlap was investigated (Dabir Micropressure

Operating Table Surface®, Dabir Surfaces, Chicago, Illinois,

USA). In a randomized controlled trial(21), the surface

tested was an alternating air cushion from the Chinese

manufacturer WeXuan Co.

In four studies, the results showed the superiority

of a high-tech support surface in relation to low-tech

surfaces in the prevention of PI in the intraoperative

period(17,21,24-25). In a randomized controlled trial(19), the

experimental group (high-tech support surface) had

a lower incidence of PI (2/98) than the control group

(7/100), however, there was no statistically significant

difference between the groups (p=0.172).

In conducting the two non-randomized studies

included in the review, there are similarities in terms

of research design, population and tested support

surfaces(24-25). In both, in the experimental group, low-

profile alternating pressure overlay was tested. This

overlay incorporates hundreds of supporting nodules

arranged in rows that periodically inflate with air, so the

patient’s weight is distributed over small nodal points of

alternating contact. Alternate rows are interconnected

so that the overlay has two areas that are alternately

inflated. Inflation/deflation of the rows is computer

controlled and provides temporary localized relief of

micropressure in areas of the body lying above deflated

nodules. The overlay was placed on top of the standard

operating table mattress, before starting the surgery.

The operating room is considered as a place of risk

for the development of PI, due to strict restrictions specific

to the environment, namely: the inability to reposition

the patient during the anesthetic surgical procedure for

pressure relief and the need of permanence on a stable

support surface, generally implying the use of a relatively

rigid padding material, resulting in the exposure of the

body to tissue deformation conditions. In this context, low-

profile alternating pressure overlay was designed for use

in surgery, which brought technological advances in a field

in which contemporary technology is generally poor(26).

In the last category (comparison between low-tech

support surfaces) two non-randomized studies(22-23) and

one randomized controlled trial were included(18). In a

non-randomized study(22), two operating table mattresses

and an overlay of dry viscoelastic combined in different

ways were tested with the participation of 505 patients

(divided into six groups). Regarding PI development, dry

viscoelastic polymer overlay was more effective than foam

and gel or standard mattresses.

In the other non-randomized study(23), two support

surfaces were tested on the same patient, and on the

right side a high-density foam pad (32 kg/m3), 50%

resilience and 10 cm thickness was applied (chest and iliac

crest) and on the left side the viscoelastic polymer pillow

(Action®, model 40700; Action, Hagerstown, Maryland,

USA), two-cm-thick, also on the chest and iliac crest.

Mean pressures and peak pressures were significantly

lower at the points evaluated with the viscoelastic polymer

pad, compared to the points tested with the high-density

foam pad. However, the results did not show a statistically

significant difference in the incidence of pressure injury

between the two support surfaces tested (OR=0.47, 95%

CI, 0.11-1.99).

In the randomized controlled trial(18), also included in

this category, patients in the control group used devices

according to the criteria of each nurse. Options included

gel pads, egg box foam mattress and “foam donuts”

for heels and elbows. The patients in the intervention

group were placed on a special foam cover with a 25%

indentation force (IF) of 30 pounds and a density of

1.3 (specification considered ideal). The number of

participants in the experimental group (55/206) showed

significantly higher occurrence of PI than those in the

control group (34/207) (p=0.0111), indicating that the

special foam surface that was tested was not effective in

preventing this type of injury.

The standard surgical table mattress is usually made

of two-inch (5.08 cm) elastic foam and covered with black

vinyl fabric. Despite its excellent stability, there is evidence

that this type of surface contributes to the development

of PI. On the other hand, mattresses made with high-

specification foam can reduce the development of this

type of injury. Thus, the multi-layer smooth surfaces

allow the patient to sink into the underlayer and wrap

around the body to increase the contact area by up to

60%. Such properties help to distribute pressure over

a larger area. Bi-elastic layers also reduce skin creases

and shear forces(27).

The support surface must have the best

characteristics to provide effective pressure redistribution,

which are: lowest mean interface pressure, lowest peak

interface pressure and highest skin contact area. Based on

these assumptions, researchers conducted a comparative

descriptive study with volunteers to investigate four types

of support surfaces, with the aim of identifying the most

effective surface for pressure redistribution in prolonged

surgical procedures. The surfaces tested were: a) standard

surgical table surface, made of three-layer viscoelastic

foam; b) static air-inflated seat cushion that was used

under the sacral area and placed on the standard surgical

table surface; c) two-layer surgical table surface, with

the upper layer of gel and the lower layer of high-density

foam; d) surgical surface for simulating fluid immersion.

The results indicated that, although all surfaces had similar

mean interface pressures, the air-inflated static seat

cushion had the best pressure redistribution properties

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10 Rev Latino-Am. Enfermagem 2021;29:e3493.

in the sacral region, compared to the other surfaces

tested(28).

The results of the systematic review showed that

high-tech support surfaces are more effective than

low-tech ones (evidence through meta-analysis) in the

intraoperative period. These results have implications

for clinical practice, since the implementation of this

technology requires a high financial investment from

the health service, that is, a reality that is probably

distant in developing countries. On the other hand, when

comparing low-tech support surfaces with regular care,

the assessment of the certainty of the evidence was very

low, indicating that conducting further research is likely

to change the estimate of the effect. In short, conducting

well-designed randomized controlled trials, testing low-

tech support surfaces, may contribute to decision-making

by perioperative nurses in clinical practice, especially

in developing countries. The evidence generated may

help this professional in planning and implementing

effective support surfaces for the prevention of PI in the

intraoperative period.

Despite the extensive search carried out in seven

databases, as well as the absence of time and language

limitations, the identification of a small number of

randomized controlled trials can be considered a

limitation, since this type of study is the most suitable

for investigating the effectiveness of health interventions.

In addition to this aspect, the researchers delimited the

inclusion of primary studies indexed in the selected

databases, that is, the non-inclusion of gray literature;

this was due to the difficulty of accessing and handling

this type of material. This decision can also be considered

as a limitation.

Conclusion

The results of the meta-analysis conducted indicated

that when comparing low-tech support surfaces with

regular care, there was no statistically significant

difference. Furthermore, the considerable heterogeneity

between the studies and the very low certainty of the

evidence is highlighted, indicating that the conduct of other

researches is likely to change the estimate of the effect.

When comparing high-tech and low-tech support

surfaces, there was a statistically significant difference

between the investigated interventions, with high-tech

being the most effective. Furthermore, it is noteworthy

that heterogeneity can be classified as not important

and the assessment of the certainty of the evidence was

moderate.

Based on the above, it is recommended to conduct

well-designed randomized controlled trials to investigate

support surfaces for the prevention of pressure injuries

in the intraoperative period, considering the cost-

effectiveness of the technology.

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Authors’ Contribution:

Study concept and design: Carolina Beatriz Cunha

Prado, Cristina Maria Galvão. Obtaining data: Carolina

Beatriz Cunha Prado, Elaine Alves Silva Machado, Karina

Dal Sasso Mendes, Cristina Maria Galvão. Data analysis

and interpretation: Carolina Beatriz Cunha Prado,

Elaine Alves Silva Machado, Karina Dal Sasso Mendes,

Renata Cristina de Campos Pereira Silveira, Cristina

Maria Galvão. Statistical analysis: Carolina Beatriz

Cunha Prado, Renata Cristina de Campos Pereira Silveira,

Cristina Maria Galvão. Drafting the manuscript: Carolina

Beatriz Cunha Prado, Elaine Alves Silva Machado, Karina

www.eerp.usp.br/rlae

12 Rev Latino-Am. Enfermagem 2021;29:e3493.

Received: Mar 7th 2021
Accepted: Jul 10th 2021

Copyright © 2021 Revista Latino-Americana de Enfermagem
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Corresponding author:
Cristina Maria Galvão
E-mail: [email protected]

https://orcid.org/0000-0002-4141-7107

Associate Editor:
Maria Lúcia Zanetti

Dal Sasso Mendes, Renata Cristina de Campos Pereira

Silveira, Cristina Maria Galvão. Critical review of the

manuscript as to its relevant intellectual content:

Carolina Beatriz Cunha Prado, Elaine Alves Silva Machado,

Karina Dal Sasso Mendes, Renata Cristina de Campos

Pereira Silveira, Cristina Maria Galvão.

All authors approved the final version of the text.

Conflict of interest: the authors have declared that

there is no conflict of interest.

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