Schultz 1999.

Study characteristics
Methods	Study objective: to evaluate a special operating room (OR) mattress overlay in preventing pressure ulcer development Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: 6 days after surgeries Number of arms: 2 Single centre or multi‐sites: single centre Study start date and end date: not described Setting: operating room (hospital)
Participants	Baseline characteristics Inclusion criteria: patients scheduled for inpatient care, 18 years of age or older, with surgery scheduled to last longer than 2 hours in the lithotomy or supine position Exclusion criteria: patients with an existing pressure ulcer, patients with severe chronic skin problems, or patients receiving only local anaesthesia Sex (M:F): 133:73 in experimental; 133:74 in control Age (years): mean 65.68 (SD 11.66) in experimental; 65.73 (12.87) in control Baseline skin status: mean Braden 22.15 (SD 1.98) in experimental; 22.41 (1.34) in control; free of existing ulcers Group difference: no difference Total number of participants: n = 413 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics New mattress overlay Description of interventions: the special mattress overlay, ... made of foam with a 25% indentation load deflection (ILD) of 30 pounds and a density of 1.3 NPIAP S3I classification: non‐powered, reactive foam surface; density 20.8 kg/m3, 25% ILD of 30 pounds Co‐interventions: all open heart surgery patients had gel pads placed under their buttocks Number of participants randomised: n = 206 Number of participants analysed: n = 206 Usual perioperative care/standard surgical care Description of interventions: patients in the control or "usual care" group were padded, based on the discretion of the individual nurse. Padding options included gel pads, foam egg crate mattresses, and foam donuts for the heels and elbows. NPIAP S3I classification: standard hospital surface Co‐interventions: all open heart surgery patients had gel pads placed under their buttocks Number of participants randomised: n = 207 Number of participants analysed: n = 207
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: 6 days Reporting: partially reported Measurement method (e.g. scale, self‐reporting): using the pressure ulcer classification system that is equivalent to NPIAP/EPUAP system Definition (including ulcer stage): the number of subjects developing ulcers of stage I or higher Dropouts: not described, probably no missing Notes (e.g. other results reported): 55 of 206 individuals having ulcers of stage I or higher in experimental (6 stage II and 49 stage I); 34 of 207 in control (3 stage II and 31 stage I) 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: Risk factors of ulcer development analysed but not extracted
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Again, using a random number table, patients were then assigned to the control or the experimental group by a principal investigator" Comment: low risk of bias due to 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	Outcome group: all outcome (primary outcome) Quote: "... the study group designation was blinded to all nursing personnel" Comment: unclear because no information provided on participants' blinding.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome group: all outcome (primary outcome) Quote: "Beginning on the day after surgery and continuing for six days, two research assistants, blinded to the study group of the patient, examined the skin over the bony prominences of each patient for any evidence of skin changes" Comment: low risk of bias because outcome assessors were blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcome group: all outcomes (primary outcome) Comment: no attrition.
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.