Clinical evaluation of liquid crystal skin thermometers

We have examined two types of liquid crystal thermometers (LCT) designed for clinical use: one designed to measure skin surface temperature (LCTS) and the other had its calibration shifted by 1.9 degrees C to read a "core" temperature (LCTC). In laboratory tests with LCT on a glass beaker, there were highly significant correlations between temperatures measured by thermocouples, LCTS (r = 0.99) and LCTC (r = 0.99). In five patients undergoing cooling and warming during cardiopulmonary bypass with an LCT on their forehead, next to a thermocouple, the smallest correlation coefficient was 0.92. In 7.3% of observations in patients, the LCT scale was blurred, but readable. The graph relating LCT temperature and forehead thermocouple temperature showed hysteresis between the cooling and warming phases. An additional laboratory experiment suggested that LCT might be affected by draughts; they should therefore be protected from draught in use.