Objective To characterise and compare the effectiveness of sacral dressings at alleviating the transfer of shear forces to the skin and therefore to lower the risk and prevention of pressure injury (PI) development in bed bound patients. Dressings were evaluated against a ratio of applied to transferred shear and peak shear force observed at the skin. Method The evaluation was undertaken using a custom benchtop in-vitro experimental setup replicating the skin-bedsheet interface. Forces were applied using an automated test rig within which a pair of load cells (ATI Nano-17) were embedded, tracking the applied normal and shear forces. Normal loading regimes of 11.1 N (6 kPa) and 14.8 N (8 kPa) were applied, to match clinically relevant sacral pressures expected. Pressures were applied with an error of 2.3% and 0.6%, respectively. No significant difference was found in the loading of dressings (P < 0.001).
Results The performance of five dressing designs were assessed, with six samples taken for each. All dressings were found to improve significantly (P < 0.001) in performance relative to the control dataset for the dynamic coefficient of friction (DCoF), peak shear at skin (F ̂ _τ) and shear ratio (τratio). The Allevyn Life (AllLi) achieved the lowest DCoF (0.372 ± 0.052) with a significant (P < 0.001) difference in other groupings. There was no significant difference between Mepilex Border (MepB) and Medline Optifoam Gentle SA Generation 4 lower specification (OfGen4-LT; P > 0.05; 0.442 ± 0.039), and Medline Optifoam Gentle SA Generation 3 (OfGen3) and OfGen4 higher specification (OfGen4-HT; P > 0.05; 0.512 ± 0.029). AllLi and OfGen4-LT achieved the lowest peak shear recorded at the skin (1.01 ± 0.07 N) with a significant difference (P < 0.001) to MepB, OfGen3 and OfGen4-HT (1.17 ± 0.14 N). At 8kPa OfGen3, AllLi and OfGen4-LT (1.57 ± 0.08 N) performed significantly lower (P < 0.001) than MepB and OfGen4-HT (1.67 ± 0.22 N). With no significant difference within groups. For the shear ratio, at 6 kPa, the OfGen4 (0.2 ± 0.007) pair exhibited superior performance (P < 0.001) to OfGen3 (0.216 ± 0.01). However, at 8 kPa, this was reversed, with OfGen3 (0.233 ± 0.009) performing significantly better (P < 0.05) than OfGen4 (0.245 ± 0.007). AllLi (0.233 ± 0.007 and 0.283 ± 0.013) and MepB (0.255 ± 0.011 and 0.275 ± 0.013) exhibited significantly (P < 0.001) higher ratios at both pressures.
Conclusion Although significant differences were identified between dressing type, DCoF was not indicative of dressing performance. All dressings reduced the shear observed at the skin with respect to the control. However, at higher pressures, the performance of dressings with a decoupled structure was reduced, as seen by the OfGen3 dressing exhibiting a significantly better performance at 8 kPa than its decoupled counterparts (MepB and OfGen4). Dressing compression, rather than thickness, was indicative of peak shear buffering. In conclusion, shear buffering is a complex process and performance is dependent on the compound response of the constituent dressing elements, rather than being dominated by a single component.
