Park 2017.

Study characteristics
Methods	Study objective: to compare a viscoelastic foam overlay (VEFO) to a standard hospital mattress for pressure injury (PI) prevention Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: 2 weeks Number of arms: 2 Single centre or multi‐sites: single centre Study start date and end date: data collected from October 2013 to November 2014 Setting: hospital (Samsung Medical Center)
Participants	Baseline characteristics Inclusion criteria: adults 19 years or older with intact skin (no stage 1 or other PIs or incontinence‐associated dermatitis (IAD)), a Braden Scale score of 16 or less (this cutoff point was selected because it indicates moderate PI risk and the need for more aggressive PI preventive interventions than those used for any inpatient), and body weight less than 100 kg according to the policy of the manufacturer of the VEFO tested in this study. Exclusion criteria: not reported Sex (M:F): 65:45 overall; 31:24 in VEFO and 34:21 in control Age (years): mean 69.56 (SD 14.26) in VEFO, 64.15 (18.38) in control Baseline skin status: mean Braden score 14.71 (SD 1.60) in VEFO and 14.33 (2.01) in control; all at risk, no existing ulcers Group difference: no difference Total number of participants: n = 122; 110 analysed Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Viscoelastic foam overlay (VEFO) Description of interventions: viscoelastic polyurethane polyester foam overlay (Viscosafe Overlay Yellow/Pink 111‐45; Safe4Care ApS, Soro, Denmark), placed on top of our standard hospital mattress ... its indentation hardness was 40%, its length was 191 cm, and its width was 90 cm. The core was an open‐cell foam with characteristic viscosity and elasticity of 3 cm, respectively. The outer cover of the VEFO is also made of an elastic polyester material designed to be waterproof, breathable and reduce friction. NPIAP S3I classification: non‐powered, reactive foam surface Co‐interventions: standard ulcer prevention care bundle including turning and repositioning Number of participants randomised: n = 59 Number of participants analysed: n = 55 Standard hospital mattress Description of interventions: had a height of 6 cm and a regenerated compressed sponge with a 4‐ to 5‐fold stronger compressive force than that of a general sponge; the mattress is covered with a polyvinyl chloride material NPIAP S3I classification: standard hospital surface Co‐interventions: standard ulcer prevention care bundle including turning and repositioning Number of participants randomised: n = 63 Number of participants analysed: n = 55
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: 2 weeks Reporting: partially reported Measurement method (e.g. scale, self‐reporting): determined using the staging system described in guidelines from the NPIAP, EPUAP, and PPPIA 2014 Definition (including ulcer stage): incidence of ulcers of any stages Dropouts: 4 of 59 in VEFO and 8 of 63 in control Notes (e.g. other results reported): 2 of 55 (3.6%) in VEFO (1 Stage 1 and 1 Stage 2) vs. 15 of 55 (27.3%) in control (7 Stage 1, 7 Stage 2 and 1 Stage 3); Chi2 11.75, P = 0.001 Time to pressure ulcer incidence Reporting: not reported Support‐surface‐associated patient comfort Reporting: not reported All reported adverse events using allocated support surfaces Reporting: not reported Health‐related quality of life (HRQOL) Reporting: not reported Cost‐effectiveness Reporting: not reported Outcomes that are not considered in this review but reported in trials: Interface pressure outcome
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Participants were randomly allocated to groups using a 1:1 allocation generated via a computer‐based program" Comment: low risk of bias because of the use of a proper randomisation method.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Comment: no information provided.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: no information provided.
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "We enrolled 122 subjects; 59 were randomly allocated to the experimental group and 63 to the control group ... the final sample comprised 110 subjects; 55 were allocated to the experimental group and 55 in the control group" Quote: "5 subjects transferred to different nursing units during data collection, 3 were found to have PI, IAD, or other skin diseases during the study ..." Comment: high risk of bias because even though the overall dropout rate (9.8%) is not high, some missed participants had incident pressure ulcers during the study.
Selective reporting (reporting bias)	Low risk	Comment: the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified.
Other bias	Low risk	Comment: the study appears to be free of other sources of bias.