Elucidation of Ischemic Mechanisms of Early Pressure Injury during Post-Decompression and Detecting Methods

Abstract

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.

Keywords: CRTT; early PI; ischemia; post-decompression; rat models.

Figure 1

Schematic illustration of blanchable erythema and early pressure injury models in rats. Blanchable erythema (BE) and early pressure injury (PI) were produced in rats by pressing the dorsal skin for different time periods. A 2% Evans Blue (EB) solution was intravenously injected to evaluate ischemia, and ink was perfused from the left ventricle to distinguish thrombi and post-mortem blood clots. i.v.: intravenous injection.

Figure 2

Assessment of ischemia: (A) illustration of the procedure for the capillary refill time test (CRTT); (B) the CRTT was performed after the transparent disc method by applying temporary pressure (150 mmHg) on the erythema after depression in the BE and early PI group (upper). The a* values represent the blood flow of the following periods: blank indicates pre-pressure, red color indicates 1 s after depression, and black color indicates 5 s post-depression (bottom).

Figure 3

Analysis of BE and early PI after EB injection: (A)representative pictures of BE and early PI before and after EB injection. EB solution was injected at 0, 5, 10, and 15 min post-decompression. Normal skin was observed as a normal reference; (B) reflectance represented the spectroscopic measurement of BE and early PI at 620 nm absorbance. Data are expressed as the mean ± SEM. n = 8 for each group. ** p < 0.001.

Figure 4

Images of pathological observation and quantification of thrombi: (A) the parts with ink perfusion showed post-mortem blood clots. On the other hand, the parts without ink perfusion in the small artery showed thrombus formation post-decompression in the early PI group, which may indicate a cause of circulatory disorder; (B) the percentage of thrombus in the three groups. The percentages of arteriovenous thrombus in the total blood vessels of the models were calculated. Values are the mean ± SEM, n = 8 for each group. ** p < 0.001.

Figure 5

Representative images of macroscopic observation.

Figure 6

Quantitation of ischemia by the CRTT: (A) a* values at certain times post-decompression in the three groups. In this image, 1 s represents the a* values at 1 s after depression, and 5 s represents the a* value at 5 s after depression; (B) the ratio of refill time was expressed as above. The a* values were recorded at pre-pressure and 1 s and 5 s after depression. Then, the a* values in the normal skin group, at 0 min post-decompression in the BE group, and 6 h post-decompression in early PI group were chosen. In this image, 1 s after depression/pre-pressure and 5 s after depression/pre-pressure represent the refill time, and 1 s/5 s represents a delayed refill time. * p < 0.05, ** p < 0.001. n = 8.