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.

Background: Pressure injuries (PIs) generally result from prolonged ischemia through localized skin compression, and ischemia persists and exacerbates damage even post-decompression. The mechanisms of ischemia post-decompression are still unclear, and appropriate methods for detection are lacking. Methods: We used blanchable erythema (BE) and early PI rat models. We assessed the perfusion using Evans Blue (EB) and thrombus formation under a light microscope. Furthermore, we performed a capillary refill time test (CRTT) to detect ischemia after depression coupled with the transparent disk method using a spectrophotometer. Results: Compared with the BE group, the early PI group showed significantly slow and insufficient perfusion, as determined by EB staining (p < 0.001). Histological observations revealed that ischemia during post-decompression of early PI was caused by a greater amount of thrombi. The CRTT results showed that although both groups exhibited varying degrees of insufficient refilling volume, the early PI group had significantly slower refilling than the BE group (p < 0.001), which persisted during the deterioration or disappearance of erythema. Conclusions: Our results showed that persistent ischemia caused by thrombi is an important cause of early PI deterioration post-decompression. Therefore, the performance of CRTT coupled with the transparent disc method may become a promising method for detecting ischemia post-decompression.