Monitoring of Surgical Wounds with Purely Textile, Measuring Wound Pads—III: Detection of Bleeding or Seroma Discharge by the Measurement of Wound Weeping

Abstract

To enable stating a final common sensor design of purely textile, measuring wound pads for the monitoring of surgically provided wounds with regard to tissue temperature, moisture release and stretching (as indicators for the most prominent wound healing disruptions bacterial inflammation, bleeding/seroma discharge, and haematoma/seroma formation), the aim of this investigation was to identify and quantify possible variables practically affecting the detection of water in a systematic study. The textile sensors comprise insulated electrical wires stitched onto a textile backing and parallel wires form a plane sensor structure whose electrical capacitance is increased by water (contained in blood or lymph) in the textiles. Only parallel sensor wires forming double meanders were examined because this structure enables all the parameters of interest to be measured. Surprisingly the results are complex, neither simple nor consistent. The change in electrical capacitance (measuring signal) upon the standardized addition of water was not additive, i.e., it was not found to be correlated to the moistened area of the sensor array, but inversely correlated to the diameter of the sensor wire, mildly pronounced in connection with smaller stitching spacing (stitching loops along the sensor wires). The measuring signal reached a maximum with medium sensor wire spacings and pronounced with a smaller stitching spacing. Without exception, the measuring signal was systematically higher in connection with smaller (compared with larger) stitching spacings. The results presented indicate that the optimization of the capacitive textile sensors cannot be calculated but must instead be carried out empirically.