Van Leen 2011.

Study characteristics
Methods	Study objective: to evaluate the clinical efficacy of combining a standard 15 cm cold foam mattress with a static air overlay mattress versus a cold foam mattress alone in preventing pressure ulcers Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: 6 months Number of arms: 2 Single centre or multi‐sites: single centre Study start date and end date: March 2002 and October 2004 Setting: nursing home
Participants	Baseline characteristics Inclusion criteria: age > 65, a Norton score between 5 and 12 and informed consent of the patients or their representatives in case of mental disorders Exclusion criteria: a pressure ulcer in the previous 6 months Sex (M:F): 9:33 in static air; 7:34 in cold foam Age (years): mean 81.1 (SD 8.37) in static air; 83.1 (7.86) in cold foam Baseline skin status: Norton score presented by subgroups; Norton scale score lower than 12 (lower than 14 = at risk for pressure ulcers) and no existing ulcers Group difference: more patients in static air having a very low Norton score (i.e. more pressure ulcer‐prone patients) Total number of participants: n = 83 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Cold foam mattress Description of interventions: standard 15 cm cold foam mattress NPIAP S3I classification: non‐powered, reactive foam surface Co‐interventions: standardised the pressure reduction in sitting position by using a static air cushion Number of participants randomised: n = 42 Number of participants analysed: n = 42 Static air overlay Description of interventions: a combination of standard 15 cm cold foam mattress with static air overlay NPIAP S3I classification: non‐powered, reactive air surface Co‐interventions: standardised the pressure reduction in sitting position by using a static air cushion Number of participants randomised: n = 41 Number of participants analysed: n = 41
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: not specified Reporting: partially reported Measurement method (e.g. scale, self‐reporting): pressure ulcers classified by using EPUAP system Definition (including ulcer stage): the number of individuals developing a pressure ulcer grade 2, 3 and 4 at the heel or in the sacral/hip region Dropouts: not described Notes (e.g. other results reported): 2 of 41 in static air mattress (1 Grade 2 and 1 Grade 3); 7 of 42 in cold foam mattress (2 Grade 2; and 5 Grade 3) 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: Treatment data on the new ulcers reported but not extracted
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Randomization into two groups was performed after informed consent using numbered envelopes" Comment: unclear risk of bias because the randomisation method used is not sufficiently clear.
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Outcome group: all outcomes (primary outcome) Comment: no information provided.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome group: all outcomes (primary outcome) Quote: "A weekly inspection of the skin to assess the possible occurrence of a skin lesion was done by an independent nurse" Comment: low risk of bias because the attempt was made to blind outcome assessment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcome group: all outcomes (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	Low risk	Comment: the study appears to be free of other sources of bias.