Bliss 1995a.

Study characteristics
Methods	Study objective: to identify inexpensive and, if possible, non‐mechanical constant low pressure overlays effective for patients at long‐term risk in continuing‐care wards for elderly people Study design: randomised controlled trial (a poorly designed multi‐arm multi‐stage trial, with re‐randomisation) Study grouping: parallel group Duration of follow‐up: not given; assessment with a mean of 17.7 days Number of arms: 7 (the trial had a Vaperm as control arm but its participants were not randomised. Vaperm data were not extracted for this review) Single centre or multi‐sites: not specified Study start date and end date: not described Setting: hospital
Participants	Baseline characteristics Inclusion criteria: patients liable to pressure sores; including those who already had superficial breaks in the skin of the pressure areas Exclusion criteria: patients with superficial sores > 5 cm and discoloured areas > 2 cm diameter Sex (M:F): overall 62:296 (treatment sessions rather than individuals) Age (years): mean 84.4 (range 67 to 97) Large cell Ripple bed (n = 71 treatment sessions of 34 patients); 85.2 (67 to 97) Preventix (n = 25 sessions of 20 patients); 85.6 (68 to 98) Groove (n = 66 sessions of 36 patients); 86.1 (68 to 98) Modular Propad (n = 60 sessions of 39 patients); 84.4 (68 to 93) Ardo Watersoft (n = 32 sessions of 22 patients); 85.6 (68 to 94) Spenco (n = 63 sessions of 35 patients); 84.3 (67 to 97) Surgicgoods Hollowcore (n = 41 sessions of 30 patients) Baseline skin status: not given; allowed inclusion of those with superficial ulcers Group difference: not given Total number of participants: n = 358 sessions of 216 patients Unit of analysis: treatment sessions of patients Unit of randomisation (per patient): treatment sessions of patients
Interventions	Intervention characteristics Groove Description of interventions: a contoured 10 cm thick foam overlay NPIAP S3I classification: non‐powered, reactive foam surface; lack of information for specifying foam characteristics Co‐interventions: not described Number of participants randomised: n = 66 sessions of 36 patients Number of participants analysed: n = 66 sessions of 36 patients Spenco Description of interventions: 1‐piece cotton hollow‐core fibrefill NPIAP S3I classification: non‐powered, reactive fibre surface Co‐interventions: not described Number of participants randomised: n = 63 sessions of 35 patients Number of participants analysed: n = 63 sessions of 35 patients Propad Description of interventions: Modular Propad was an 8.5 cm thick foam pad with the upper surface moulded into air‐ducted, rounded horizontal blocks NPIAP S3I classification: non‐powered, reactive foam surface; lack of information for specifying foam characteristics Co‐interventions: not described Number of participants randomised: n = 60 sessions of 39 patients Number of participants analysed: n = 60 sessions of 39 patients Preventix Description of interventions: a 16 cm thick mat of 8 cm square foam modules of different densities inserted into a flexible PVC frame ... providing a variably soft, contoured, slit surface to optimize pressure distribution NPIAP S3I classification: non‐powered, reactive foam surface; lack of information for specifying foam characteristics Co‐interventions: not described Number of participants randomised: n = 25 sessions of 20 patients Number of participants analysed: n = 25 sessions of 20 patients Surgicgoods Description of interventions: Surgicgoods Hollowcore Mattress pad was a 1‐piece fibrefill NPIAP S3I classification: non‐powered, reactive fibre‐filled surface Co‐interventions: not described Number of participants randomised: n = 41 sessions of 30 patients Number of participants analysed: n = 41 sessions of 30 patients Watersoft Description of interventions: Ardo Watersoft consisting of three 4 cm deep, partly‐filled water cushions with stabilising baffles NPIAP S3I classification: non‐powered, reactive water‐filled surface Co‐interventions: not described Number of participants randomised: n = 32 sessions of 22 patients Number of participants analysed: n = 39 sessions of 22 patients Large cell Ripple bed Description of interventions: consisting of 14 horizontal cells 10 cm in diameter in the centre, connected in 2 alternating series powered by a small pump which caused them to inflate and deflated reciprocally underneath the patient every 10 minutes, thus continually changing the supporting points of pressure NPIAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: not described Number of participants randomised: n = 71 sessions of 34 patients Number of participants analysed: n = 71 sessions of 34 patients
Outcomes	Proportion of participants developing a new pressure ulcer Not reported Notes (e.g. other results reported): numbers of trials in which sores developed or worsened: 11 of 71 Ripple bed; 9 of 25 Preventix; 27 of 66 Groove; 26 of 60 Propad; 19 of 32 Watersoft; 38 of 63 Spenco; 26 of 41 Surgicgoods Time to pressure ulcer incidence Not reported Support‐surface‐associated patient comfort Not reported All reported adverse events using allocated support surfaces Not reported Health‐related quality of life (HRQOL) Not reported Cost‐effectiveness Not reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "the patient was randomly allocated to an experimental overlay by the researcher writing the names of all those available at the time on slips of paper which were folded and offered to the nurse to choose one blind" Comment: low risk of bias because drawing of lots is applied to generate random sequence.
Allocation concealment (selection bias)	High risk	Quote: "the patient was randomly allocated to an experimental overlay by the researcher writing the names of all those available at the time on slips of paper which were folded and offered to the nurse to choose one blind. The designated overlay was then placed on the bed" Comment: high risk of bias because it appears difficult to conceal the allocation process as the authors. described. The nurse would have knowledge of which overlays were available at the time of consent.
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	Unclear risk	Comment: no information provided.
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: high risk of bias because some individuals may be repeatedly observed and included in analysis (i.e. correlation issue in analysis). For example, Bliss stated "there were no written criteria determining the decision to stop a trial [i.e. using an overlay as the experimental intervention]. This depended mainly on these experienced nurses' unwillingness to allow it to continue because of enlargement of an existing sore, a new blister, discolouration, oedema ... Patients who developed pressure damage between assessments might also be taken off their overlay ... if they later improved ... they were re‐randomized for another trial period [i.e. comparisons of new overlays]". Additionally, overlays were observed for unequal periods of time. Treatments were discontinued or introduced without pre‐specified stopping rules. Some comparisons are not parallel.