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. 2021 May 10;2021(5):CD013620. doi: 10.1002/14651858.CD013620.pub2

Nixon 2006.

Study characteristics
Methods Study objective: to compare whether differences exist between alternating pressure overlays and alternating pressure mattresses in the development of new pressure ulcers, healing of existing pressure ulcers, and patient acceptability.
Study design: randomised controlled trial with cost‐effectiveness analysis
Study grouping: parallel group
Duration of follow‐up: 30 days; 60 days
Number of arms: 2
Single centre or multi‐site: multi‐site
Study start date and end date: not described
Setting: NHS hospitals
Participants Baseline characteristics
Inclusion criteria: participants aged at least 55 years who had been admitted to vascular, orthopaedic, medical, or care of elderly people wards, either as acute or elective admissions, in the previous 24 hours; expected length of stay of at least 7 days and either limitation of activity and mobility (Braden scale activity and mobility scores of 1 or 2; box 25) or an existing pressure ulcer of grade 2 (using the skin grading tool from Nixon et al, 3 box 1); elective surgical patients without limitation of activity and mobility or an existing pressure ulcer
Exclusion criteria: those who had a pressure ulcer on admission of grade 3 or worse, had a planned admission to an intensive care unit after surgery, were admitted to hospital more than 4 days before surgery, slept at night in a chair, or weighed more than 140 kg or less than 45 kg
Sex (M:F): 346:636 in mattress; 365: 624 in overlay
Age (years): mean 75.0 (SD 9.2) in mattress; 75.4 (SD 9.7) in overlay
Baseline skin status: total Braden scores not reported; 1558 (79%) of patients bedfast and 1342 (68.1%) patients very limited mobility and 362 completely immobile
Group difference: no difference
Total number of participants: 1972
Unit of analysis: individuals
Unit of randomisation (per patient): individuals
Interventions Intervention characteristics
Alternating pressure mattress
  • Description of interventions: consist of air‐filled sacs that sequentially inflate and deflate to relieve pressure for short periods; provided as a full size replacement mattress; with 7.5– to 30‐minute cycle

  • NPIAP S3I classification: powered, alternating pressure (active) air surface

  • Co‐interventions: not described

  • Number of participants randomised: n = 982

  • Number of participants analysed: n = 982


Alternating pressure overlay
  • Description of interventions: consist of air‐filled sacs that sequentially inflate and deflate to relieve pressure for short periods; provided as a shallower overlay that is placed on top of a mattress; with 7.5– to 30‐minute cycle

  • NPIAP S3I classification: powered, alternating pressure (active) air surface

  • Co‐interventions: not described

  • Number of participants randomised: n = 990

  • Number of participants analysed: n = 989

Outcomes Proportion of participants developing a new pressure ulcer
  • Outcome type: binary

  • Time points: 60 days

  • Reporting: fully reported

  • Measurement method (e.g. scale, self‐reporting): staff nurses rated and validated by researchers; using the ulcer classification system evaluated in Nixon 2006 (see the seventh reference of Nixon 2006 for the detail of the system).

  • Definition (including ulcer stage): the proportion of participants developing 1 or more new pressure ulcers of grade 2 or worse; proportions of participants developing a new ulcer within 30 days

  • Dropouts: 1 excluded

  • Notes (e.g. other results reported): 60 days: 101 of 982 in mattress (5 grade 3; probably the rest all grade 2); 106 of 989 in overlay (3 grade 3; probably the rest all grade 2); 30 days: 91 (9.3%) in mattress and 99 (10.0%) in overlay (Chi2, P = 0.58).


Time to pressure ulcer development
  • Outcome type: time‐to‐event

  • Time points: 60 days

  • Reporting: fully reported

  • Measurement method (e.g. scale, self‐reporting): see above

  • Definition (including ulcer stage): time to development of new pressure ulcers

  • Dropouts: 1 excluded

  • Notes: figure 5 (a,b) presented Kaplan‐Meier curves of the time to develop a new pressure ulcer for ITT and per protocol populations in the primary reference of Nixon 2006; for ITT, log‐rank test P value = 0.759; HR 0.96 (95% CI 0.73 to 1.26) estimated by the review authors using the methods in Tierney 2007.


Support‐surface‐associated patient comfort
  • Outcome type: binary

  • Time points: 60 days

  • Reporting: partially reported

  • Measurement method (e.g. scale, self‐reporting): self‐reported

  • Definition: patient acceptability assessed indirectly from the number of people requesting a change because they were dissatisfied with the assigned surface

  • Dropouts: 1 excluded

  • Notes: 186 of 982 (18.9%) in mattress; 230 of 989 (23.3%) people in overlay


All reported adverse events using allocated support surfaces
  • Outcome type: binary

  • Time points: 60 days

  • Reporting: partially reported

  • Measurement method (e.g. scale, self‐reporting): clinical research nurse‐rated (gained information from ward staff and healthcare records)

  • Definition: adverse events due to support surfaces allocated

  • Dropouts: not relevant

  • Notes: 377 adverse events reported for 308 patients that were not reported by study groups; 10 patients with mattress‐related events in mattress and 4 in overlay; ‘not mattress related’ adverse events also reported, but not extracted (see the primary reference of Nixon 2006).


Health‐related quality of life (HRQOL)
  • Reporting: partially reported

  • Definition: how patients, after discharged, perceive and describe their health and quality of life, their experiences of developing a pressure ulcer and their experiences of pressure area care.

  • Notes: HRQOL measured and reported as qualitative analysis results. Participants of the qualitative interviews were 23 people with experience of having a pressure ulcer, but not limited to those eligible for this trial. From patients' perspectives, the development of a pressure ulcer has physical, emotional, mental and social impacts. The development of a pressure ulcer can be pivotal in the patient’s trajectory from illness to recovery, with the development of an ulcer preventing them from making a full recovery and causing varied impacts on their quality of life.


Cost‐effectiveness
  • Outcome type: continuous

  • Reporting: fully reported in the primary reference of Nixon 2006

  • Measurement method (e.g. scale, self‐reporting): health benefit measures using Kaplan Meier estimates of restricted mean time to development of pressure ulcers. Overall costs at pricing year of 2002‐3 included hospital treatment costs per day based on estimates from the Chartered Institute of Public Finance and Accountancy; unit purchasing and rental costs of each surface based on UK retail prices provided by the manufacturers. Hopsital costs analysed by using generalised linear model. Economic analysis from the perspective of the UK NHS and Personal Social Service; no cost or benefit discounting due to time horizon shorter than 1 year; non‐parametric bootstrapping techniques applied; sampling uncertainty explored in an incremental cost effectiveness plane; sensitivity analysis conducted for 3 different scenarios.

  • Definition: incremental cost‐effectiveness ratio (ICER), the ratio of the difference in costs relative to the difference in health benefit associated with the technology under evaluation.

  • Notes: because dominance was identified, an incremental analysis is not justified and the estimates of differential costs and health benefits were not combined in an ICER. Base case analysis results: mean overall hospital costs 6793.33 (SD 8196.52) in overlay group and 6509.73 (7347.56) in mattress group and mean difference in total hospital cost of £283.60 (95% confidence interval £377.59 to £976.79, P = 0.418). Difference in the Kaplan Meier restricted estimates of the mean time to development of pressure ulcers ‐ 10.64 days (95% bias corrected confidence interval 24.40 to 3.09 days; overlay versus mattress). The mattresses are a dominant strategy when compared with the overlays; they are associated with a delay in the development of pressure ulcers and lower hospital costs. Cost‐effectiveness acceptability curve indicated that on average alternating pressure mattresses compared with alternating pressure overlays were associated with an 80% probability of being cost saving.


Outcomes that are not considered in this review but reported in trials:
  • Time to healing and grade of ulcer at trial completion.

  • Healing of existing pressure ulcers.

Notes  
Risk of bias
Bias Authors' judgement Support for judgement
Random sequence generation (selection bias) Low risk Quote: "Randomisation was through an independent, secure, 24 hour randomisation automated telephone system, ensuring allocation concealment. We used minimisation so that groups were comparable. We minimised on centre, existing pressure ulcer ... specialty ... and type of admission"
Comment: low risk of bias due to the use of a proper randomisation method.
Allocation concealment (selection bias) Low risk Quote: "Randomisation was through an independent, secure, 24 hour randomisation automated telephone system, ensuring allocation concealment. We used minimisation so that groups were comparable. We minimised on centre, existing pressure ulcer ... specialty ... and type of admission"
Comment: low risk of bias due to proper concealment.
Blinding of participants and personnel (performance bias)
All outcomes High risk Outcome group: all outcomes
Quote: "This was an open trial. Owing to the nature of the mattresses under investigation, it was not possible to mask the randomised intervention to the patients participating in the trial, ward nursing staff or the CRNs conducting the skin assessments"
Quote: "The PRESSURE Trial CRNs worked closely with ward staff and informed ward staff of the randomised mattress allocation"
Comment: high risk of bias because it was impossible to blind participants and personnel but some efforts were made to improve the compliance of using the allocated interventions.
Blinding of outcome assessment (detection bias)
All outcomes Unclear risk Outcome group: primary outcome
Quote: "This was an open trial. Owing to the nature of the mattresses under investigation, it was not possible to mask the randomised intervention to the patients participating in the trial, ward nursing staff or the CRNs conducting the skin assessments ... To minimise the potential for bias it was planned that qualified ward‐based nursing staff (WNs) would record daily skin assessments and CRNs would undertake assessments twice weekly to validate ward staff records, ward staff remaining blind to the CRN record" (HTA report).
Comment: unclear risk of bias because of the efforts to reduce detection bias.
Outcome group: adverse event
Quote: "Adverse events were reviewed by the clinical coordinator, TMG and TSC, who were blind to allocation"
Comment: low risk of bias for adverse event outcome.
Incomplete outcome data (attrition bias)
All outcomes Low risk Outcome group: All outcomes
Quote: "The analysis was by intention to treat, with participants being analysed according to the group to which they were randomised ..."
Quote: "... 1972 were randomised ... One patient was randomised twice and therefore excluded, providing an intention to treat population of 1971 people ..."
Comment: low risk of bias because intention‐to‐treat analysis was done.
Selective reporting (reporting bias) Low risk Comment: the study protocol is available and all of the study’s pre‐specified (primary and secondary) outcomes that are of interest in the review have been reported in the pre‐specified way.
Other bias Low risk Comment: the study appears to be free of other sources of bias.