Establishing an Appropriate Pressure for the Transparent Disc Method to Distinguish Early Pressure Injury and Blanchable Erythema

Background: Non-blanchable erythema is used as a diagnostic indicator for stage 1 pressure injury (early PI); it is distinguished from blanchable erythema (BE) by the application of “light pressing”. Considering the low of the accuracy of the degree of pressure applied, it is difficult to use this method in clinical settings. Methods: We constructed models of BE and early PI in order to determine the most appropriate pressure values using the transparent disc method. We observed erythema by using a Dermo-camera to quantify the gray and a* values of the wound area along with a spectrophotometer. Results: BE started to fade at 50 mmHg, while the gray values became statistically significant when the pressure was increased to 100 mmHg (p < 0.05). However, erythema remained even when the pressure was increased to 150 mmHg soon after decompression. By contrast, the early PI was showed to be non-blanchable for the longest time under a pressure of 150 mmHg, but by 18 h it had decreased and the erythema faded more obviously after applying pressure. Conclusions: We proposed that a pressure of 50–100 mmHg was more appropriate for light pressure, but this may vary when different instruments are used. Variations may occur in either BE or early PI, therefore, careful attention should be paid during observations.