| Methods |
RCT with 8‐day follow‐up. Telephone randomisation (i.e. full allocation concealment) stratified by centre, and age. |
| Participants |
Patients aged ≥ 55 y, admitted for elective major general, gynaecological or vascular surgery in supine or lithotomy position and free of preoperative pressure damage greater than grade 1.
Groups well matched at baseline for age, sex, Braden score, type of surgery, duration of surgery, length of preoperative stay, proportion of time hypotensive during surgery. |
| Interventions |
1. Dry visco‐elastic polymer pad on operating table (n = 222).
2. Standard operating theatre table mattress plus Gamgee heel support (n = 224). |
| Outcomes |
Incidence and severity of pressure ulcers:
Overall incidence of pressure ulcers of 16% (65/416):
1. Dry visco‐elastic polymer pad on operating table: 11% (22/205);
2. Standard mattress: 20% (43/211); P value 0.01, OR = 0.46; 95% CI 0.26‐0.82.
56/65 episodes of skin damage were conversions from grade 0 to grade 1 ulcers.
4/65 grade 0 to grade 2A conversions.
5/65 grade 0 to grade 2B conversions. These data were not broken down by group. |
| Notes |
A priori sample size calculation. 133 paired assessments by 94 nurses for pre‐study inter‐rater reliability assessments undertaken. Disagreement in only 2.2% assessments, and only 2 disagreements related to differentiating between grade 1 and grade 2a ulcers (the remainder were grade 0 and grade 1). The majority were associated with heel assessments. For the recovery and ward area assessments, there were discrepant assessments in only 8.5% cases. Sensitivity analysis assessing the impact of this level of misclassification on the overall result determined that the overall difference between the mattresses remained.
Main endpoint data reported for 416 patients; incomplete data for 30 patients (lost forms 3; incomplete postoperative skin assessment 27). The patients with incomplete data were not reported by group. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Stratified randomisation by centre and age: "a telephone randomisation schedule was developed within random permuted blocks of 6, with a run‐in of 8"; age as 55‐69 and 70 or over. |
| Allocation concealment (selection bias) |
Low risk |
Randomisation managed by the Northern and Yorkshire Clinical Trials and Research Unit. |
| Blinding (performance bias and detection bias)
Pressure ulcer incidence |
Low risk |
The Data Monitoring Committee and statistician were blind to treatment allocation; “the record pertaining to the intra‐operative randomised mattress allocation remained separate from the main data collection pro forma to maintain the blind” . |
| Incomplete outcome data (attrition bias)
All outcomes |
Low risk |
ITT analyses conducted. |
| Selective reporting (reporting bias) |
Low risk |
All pre‐specified outcomes reported. |
| Free of other bias ‐ were groups similar at baseline regarding the most important prognostic indicators? |
High risk |
Standard mattress group: longer length of operation, longer pre‐operative stay, more time in hypotensive state than dry polymer pad group. |
| Free of other bias ‐ was the timing of the outcome assessment similar in all groups? |
Low risk |
No other concerns. |
