Bliss 1967.

Study characteristics
Methods	Study objective: to assess different mattresses for preventing pressure sores Study design: randomised controlled trial Study grouping: parallel group Duration of follow‐up: treatment for 14 days and follow‐up assessments on the 16th day Number of arms: 2 Single centre or multi‐site: single centre Study start date and end date: not described Setting: geriatric unit
Participants	Baseline characteristics Inclusion criteria: all new patients with a Norton score of 7 or more, and all inpatients with a score 7 or more and still rising, provided they had no, or only superficial, trunk sores at the time Exclusion criteria: patients with severe sores of the trunk Sex (M:F): overall 27:56; large‐celled ripple bed 10:32; control 17:24 Age (years): overall mean 81.2; large‐celled ripple bed 80.4; control 82.1 Baseline skin status: mean baseline Norton score 10.5; free of existing severe ulcers (43 with superficial sore) Group difference: no difference in variables except for sex distributions Total number of participants: n = 83 (70 analysed) Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Large‐celled ripple bed Description of interventions: alternating pressure mattress made of large cells (6 inches / 15 cm wide) giving a depth of 4 inches (10 cm) when inflated, consisting of transverse air cells. Consisting of 14 cells, leaving a gap of 12 inches (30 cm) to accommodate the pillow at the head of the bed. Inflated and deflated by an electrically driven pump so that the patient is supported on each series of cells in turn for about four to five minutes. NPUAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: standardised care Number of participants randomised: n = 42 Number of participants analysed: n = 35 Ordinary hospital mattress Description of interventions: ordinary hospital mattress NPUAP S3I classification: standard hospital surface Co‐interventions: standardised care Number of participants randomised: n = 41 Number of participants analysed: n = 35
Outcomes	Proportion of participants developing a new pressure ulcer Outcome type: binary Time points: 14 days Reporting: partially reported Measurement method (e.g. scale, self‐reporting): ulcer incidence graded by the Bliss (1966) method Definition (including ulcer stage): incidence of trunk ulcers Dropouts: 4 on the ripple bed and 6 in the control group died, and 3 participants were on ripple bed mattresses that had deficiencies (e.g. the failure of motors, leaks of air cells) Notes (e.g. other results reported): trunk ulcers; 3 of 15 patients without existing ulcers at baseline developed new ulcers in ripple bed; 7 of 18 in control. Incident ulcer data not available for those with existing ulcers at baseline. Heel sore data not extracted due to incomplete reporting of relevant data. Time to pressure ulcer development Not reported Support‐surface‐associated patient comfort Not reported All reported adverse events using allocated support surfaces Not reported Notes: 4 on the ripple bed and 6 in the control group died Health‐related quality of life (HRQOL) Not reported Cost‐effectiveness Not reported Outcomes that are not considered in this review but reported in trials: Deficiencies of the ripple bed machine (n = 3) Ulcer changes among those with existing ulcers at baseline
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "In order to ensure that the distribution of subjects among the various regimens was as random as possible the experimental and control treatments were arranged in a rota. As patients were admitted to the trial they were allocated to the next treatment on the rota in order" Comment: unclear risk of bias because the sequence generation process is not described
Allocation concealment (selection bias)	Unclear risk	Comment: no information provided
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Outcome group: ulcer incidence Comment: no information provided
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome group: ulcer incidence Quote: "The record forms were all evaluated in a single session by one observer, each being masked in such a way that it was not possible to know to which patient or to which experimental regimen it referred" Comment: low risk of bias because the blinding of assessment is stated
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Outcome group: ulcer incidence Comment: unclear risk of bias because 7 of 42 in ripple bed and 6 of 41 in control group were excluded from analysis
Selective reporting (reporting bias)	High 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. However, incidence outcome data among those with existing ulcers are not available.
Other bias	Low risk	Comment: the study appears to be free of other sources of bias