Esophageal stethoscope placement depth: its effect on heart and lung sound monitoring during general anesthesia

Although the esophageal stethoscope has been used for many years, the effect of the depth of placement on the quality of the sounds obtained has never been investigated. The amplitude and frequency characteristics of the first and second heart sound and of inspiratory and expiratory breath sounds were determined at various stethoscope depths (from the distal tip) in 17 healthy anesthetized adults. The amplitude for each type of sound varied markedly with depth. Maximal amplitude for S1 was at 34 +/- 3 cm, for S2 at 27 +/- 2 cm, for inspiratory breath sound at 28 +/- 2 cm, and for expiratory breath sound at 26 +/- 2 cm. There was a positive linear correlation between the depth of maximal amplitude of these sounds and patient height. Peak frequency, in general, did not change with depth. We conclude that investigators should measure and document depth when performing studies involving the esophageal stethoscope.

Analysis of sound from the esophageal stethoscope at various depths reveals that placement depth greatly affects the sounds. A depth of 28-32 cm is recommended for clinical use; S1, S2, and inspiratory and expiratory sounds have a high amplitude in that range.