Grindley 1996.

Study characteristics
Methods	Study objective: to compare the performance of the Nimbus II and the Pegasus Airwave mattresses in a hospice setting Study design: randomised controlled trial Study grouping: cross‐over design Duration of follow‐up: 3 days (the first stage of the cross‐over trial) Number of arms: 2 Single centre or multi‐site: single centre Study start date and end date: not described Setting: hospice
Participants	Baseline characteristics Inclusion criteria: patients with existing pressure sores grade 2* or above or patients without existing pressure sores but at high or very high risk of developing pressure sores (Waterlow risk assessment score of 15 or above); minimum anticipated hospice stay of 7 days; patients spending more than 6 hours in a 24‐hour period on the mattress; patients must give consent Exclusion criteria: mental frailty; existing inpatients already on either of the study mattresses; gross obesity (greater than 30 stones, 190 kg); extreme emaciation (less than 6 stones, 38 kg); unstable spinal metastases Sex (M:F): overall 8:12 Age (years): overall mean 69.05 (SD 14.32) Baseline skin status: overall median Waterlow 22.5 (range 15 to 30) mean 22.65 (SD 4.43); 8 with existing ulcers Group difference: not given Total number of participants: n = 20 Unit of analysis: individuals Unit of randomisation (per patient): individuals
Interventions	Intervention characteristics Nimbus II mattress Description of interventions: Nimbus II (Huntleigh Healthcare, Luton, Beds) is an alternating air pressure mattress replacement, comprising 2 banks of cells which alternately inflate and deflate over a 10‐minute cycle NPUAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: not described Number of participants randomised: n = 10 Number of participants analysed: the first‐stage data not available Pegasus Airwave Description of interventions: Pegasus Airwave (Pegasus Airwave, Waterlooville, Hants) is an alternating air pressure mattress replacement, with a 3‐cell alternating cycle lasting 7.5 minutes. It consists of a double layer of cells which work together as one. NPUAP S3I classification: powered, alternating pressure (active) air surface Co‐interventions: not described Number of participants randomised: n = 10 Number of participants analysed: the first‐stage data not available
Outcomes	Proportion of participants developing a new pressure ulcer Not reported Time to pressure ulcer development Not reported Support‐surface‐associated patient comfort Outcome type: Time points: Reporting: partially reported Measurement method (e.g. scale, self‐reporting): self‐rated using a questionnaire including the question: how would you describe the mattress with respect to comfort? (1 = extremely comfortable; 2 = very comfortable; 3 = comfortable; 4 = fairly comfortable; 5 = uncomfortable; 6 = very uncomfortable; 7 = extremely uncomfortable) Definition: comfort of using mattress Dropouts: mattress preference questionnaire completed by 16 patients Notes: 10 responded Nimbus II is more comfortable and 2 responded Pegasus Airwave is more comfortable. 4 responded No preference [these are the second‐phase data]. All reported adverse events using allocated support surfaces Not reported Health‐related quality of life (HRQOL) Not reported Cost‐effectiveness Not reported Outcomes that are not considered in this review but reported in trials: Sleeping quality
Notes	Challenging to contact the study authors to request data at the first stage of this cross‐over trial.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomization was performed using a random numbers table" Comment: low risk of bias because the sequence generation process is proper.
Allocation concealment (selection bias)	Low risk	Quote: "To avoid bias, the order in which the mattresses were allocated was randomised and selected by the investigator from sealed opaque envelopes in sequential order." Comment: low risk of bias because it is likely to conceal allocation properly.
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	Outcome group: comfort Quote: "mattress preference questionnaire completed by 16 patients" Comment: unclear risk of bias because no information given on which group the missing are from.
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.