Optimal Depth for Esophageal Stethoscope

"Core temperatures will be measured with a tympanic thermometer as a reference. When the tympanic membrane (TM) temperature is constant after measuring three consecutive times at 10 seconds intervals, the temperature will be assumed as the core body temperature.~Initially, the esophageal stethoscope (ES) will be inserted to a depth of 45 cm from the incisor. After 30 minutes of monitoring, when the changes in the body temperatures stabilized, initial temperatures of the TM and ES thermistor will be assessed.~After 5 minutes, ES will be taken out 2 cm back, and the temperatures of each site will be measured when the temperature change of the ES thermistor stabilized below 0.1°C. Eventually, the depth of ES will be changed from 45 to 27 cm with a 2 cm interval, and the temperature at each position will be measured."

For the further evaluation of the optimal insertion depth of GDT, anatomical landmarks such as distance from the cricoid cartilage to the carina (CCD) and distance from the carina to the intervertebral disc between T8 and T9 (CDD) will be measured using an electronic caliper on a preoperative chest X-ray.