Passive warming of airway gases (artificial nose) improves accuracy of esophageal temperature monitoring

Abstract

The most efficient site for monitoring heart and lung sounds by esophageal stethoscope is not the warmest segment of the esophagus. This study investigated the ability of passive warming of airway gases to increase the accuracy of temperatures measured at this site (i.e., to decrease their difference from core temperature). In 15 adult patients undergoing general anesthesia and endotrachcal intubation, esophageal temperatures were measured before and after use of a heat and moisture exchanger (an artificial nose) that passively warmed inspired gases. The resulting values were compared with nasopharyngeal temperatures, which represented core temperature. Before use of the heat and moisture exchanger, esophageal and nasopharyngeal temperatures differed significantly (mean difference ± SD, 0.9 ± 0.4‡C;P ≤ 0.001). After passive warming of inspired gases, esophageal temperatures increased significantly (mean increase ± SD, 0.5 ± 0.2‡C;P ≤ 0.001) but inconsistently (range, 0.1 to 1.2‡C). However, the mean difference between esophageal and nasopharyngeal temperatures was still significant (0.5 ± 0.3‡C;P < 0.001). Discrepancies between esophageal and core temperatures persist when a currently available esophageal stethoscope with adjacent auscultation chamber and temperature probe is used, despite passive warming of airway gases.