Laurent 1998.

Study characteristics
Methods	Study objective: to assess the effectiveness of 3 prevention strategies and compare them to the standard mattress Study design: randomised controlled trial Study grouping: factorial design Duration of follow‐up: mean length of stay 15.04 (SD 7.10) Number of arms: 4 Single centre or multi‐site: single centre Study start date and end date: not described Setting: hospital
Participants	Baseline characteristics Inclusion criteria: adults over 15 years of age, admitted for major cardiovascular surgery, hospital stay likely to be at least 5 days, with a period on the intensive care unit (ICU) Exclusion criteria: not reported Sex (M:F): 214:98 across 4 groups Age (years): mean 64.0 (SD 11.88) across 4 groups Baseline skin status: not described Group difference: no difference Total number of participants: n = 312 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Standard group Description of interventions: standard mattress in ICU; standard mattress postoperatively NPIAP S3I classification: standard hospital surface (ICU); standard hospital surface (postoperation) Co‐interventions: not described Number of participants randomised: n = 80 Number of participants analysed: n = 80 Alternating mattress in ICU Description of interventions: Nimbus (AP) in ICU; standard mattress postoperatively NPIAP S3I classification: powered, alternating pressure (active) air surface (ICU); standard hospital surface (postoperation) Co‐interventions: not described Number of participants randomised: n = 80 Number of participants analysed: n = 80 Constant low‐pressure mattress in postoperative hospitalisation Description of interventions: standard mattress in ICU; Tempur (CLP) postoperatively (Laurent 1998). Additional source of information: "a visco‐elastic polyethylene urethane foam mattress (Tempur®, Tempur‐World Inc., USA)" (Vanderwee 2005). NPIAP S3I classification: standard hospital surface (ICU); non‐powered reactive foam surface; high specification viscoelastic foam (postoperation) Co‐interventions: not described Number of participants randomised: n = 75 Number of participants analysed: n = 75 Both mattresses Description of interventions: Nimbus in ICU and Tempur (CLP) postoperatively NPIAP S3I classification: powered, alternating pressure (active) air surface (ICU); non‐powered, reactive foam surface; high specification viscoelastic foam (postoperation) Co‐interventions: not described Number of participants randomised: n = 77 Number of participants analysed: n = 77
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: not described Reporting: partially reported Measurement method (e.g. scale, self‐reporting): assessed by specially trained nurses and classified as stage 0 (normal skin), stage 1 (non‐blanchable erythema), and stage 2 (partial or full thickness skin loss) Definition (including ulcer stage): cumulative incidence of pressure sores of stage 2 (the lower the rate, the better the mattress effectiveness) Drop outs: not described Notes (e.g. other results reported): 45 of 312 (14.4%) having pressure sores; 14 of 80 in standard; 10 of 80 in alternating mattress in ICU; 11 of 75 in constant low pressure mattress; 10 of 77 in both mattresses Time to pressure ulcer development 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
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomised by blocks" Comment: unclear risk of bias because the randomisation method was not stated.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided
Blinding of participants and personnel (performance bias) All outcomes	High risk	Outcome group: primary outcome Quote: "Given the kind of material tested, blinding was not possible" Comment: high risk of bias as the above statement suggests.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcome group: primary outcome Quote: "Given the kind of material tested, blinding was not possible" Comment: high risk of bias as the above statement suggests.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcome group: primary outcome Comment: no attrition identified.
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	High risk	Comment: the study appears not to consider the interaction between the effects of the different interventions that results from the factorial design used.