Early Detection of Stage I Pressure Ulcers Identifying Non-Blanchable Erythema Using Electric Impedance

Purpose:  Early detection and identification of pressure ulcers is very important for the well being of patients as well as for controlling medical expenses. Under Japanese Society of Pressure Ulcers guidelines, either finger method or disk method is considered appropriate to identify such erythema or pressure ulcers, because non blanchable erythema(NBE) is not always clearly visible. Since electric impedance typically reduces resistance in interstitial fluids, measuring the impedance of skin tissue under erythema conditions can find evidence of whether StageⅠPressure Ulcer exists. The purpose of this study was to examine the relevance of impedance measurement for classifying complete NBE or partial NBE or blanchable erythema (BE) .

Methods:  Subjects involved patients who were judged to have complete NBE, partial NBE, or BE by the disk method. Impedance data were collected by the two electrodes method using an LCR METER NF Corp.. One electrode sensor was placed on the edge of an erythema and another electrode sensor was on the opposite edge of erythema. The range of frequency was 1mHZ to 100kHZ. The differences of impedance data between complete NBE , partial NBE, or BE and each opposite healthy local area to erythema were analyzed by ANOVA. Finally, to improve the accuracy of impedance difference, devised formula of total deviations which was removed erythema size effect were used .

Results:  Subjects were 23 bedbound patients, and the local areas of erythema were the thigh, knee, heel, toe, sacrum, and spinal curvature. By the disk method, five patients were classified as having complete NBE, eleven as partial NBE and seven as BE. The mean (SD) size(mm) was 18.6(12.6) in complete NBE, 10.5(12.8) in partial NBE, or 11.9(6.1) in BE. As for ANOVA analysis, a significant difference was observed among complete NBE, partial NBE and BE(p<0.05). Impedance difference for complete NBE is larger than normal control, while that for partial NBE was smaller than normal control. As there were observed a linear relation and a coefficient of determination, analysis by revised formula of total deviation, which removed erythema size effect, proved that three distribution of impedance values existed. The mean (SD) impedance data by revised formula of total deviation was 0.14(0. 03) in complete NBE, 0.52(0. 02) in partial NBE and 0.34(0.02) in BE, and a significant difference was observed (p<0.001).

Conclusion:  The result of this work indicate that complete NBE can predict blood flow disturbance , while partial NBE can predict complicated skin tissue conditions of vessel dilation or increasing interstitial fluids, and there may be possibility of skin damage. Therefore, there is possibility of developing a new early detective and identifiable device of StageⅠpressure ulcer using electric impedance. In the future ,we will use a larger sample size and clarify the difference between complete and partial NBE, additionally using a blood flow measurement and a digital erythema color instrument.