title: A visual stethoscope to detect the position of the tracheal tube.
abstract: BACKGROUND
  Advancing a tracheal tube into the bronchus produces unilateral breath sounds. We created a Visual Stethoscope that allows real-time fast Fourier transformation of the sound signal and 3-dimensional (frequency-amplitude-time) color rendering of the results on a personal computer with simultaneous processing of 2 individual sound signals. The aim of this study was to evaluate whether the Visual Stethoscope can detect bronchial intubation in comparison with auscultation.
  
  
  METHODS
  After induction of general anesthesia, the trachea was intubated with a tracheal tube. The distance from the incisors to the carina was measured using a fiberoptic bronchoscope. While the anesthesiologist advanced the tracheal tube from the trachea to the bronchus, another anesthesiologist auscultated breath sounds to detect changes of the breath sounds and/or disappearance of bilateral breath sounds for every 1 cm that the tracheal tube was advanced. Two precordial stethoscopes placed at the left and right sides of the chest were used to record breath sounds simultaneously. Subsequently, at a later date, we randomly entered the recorded breath sounds into the Visual Stethoscope. The same anesthesiologist observed the visualized breath sounds on the personal computer screen processed by the Visual Stethoscope to examine changes of breath sounds and/or disappearance of bilateral breath sound. We compared the decision made based on auscultation with that made based on the results of the visualized breath sounds using the Visual Stethoscope.
  
  
  RESULTS
  Thirty patients were enrolled in the study. When irregular breath sounds were auscultated, the tip of the tracheal tube was located at 0.6 +/- 1.2 cm on the bronchial side of the carina. Using the Visual Stethoscope, when there were any changes of the shape of the visualized breath sound, the tube was located at 0.4 +/- 0.8 cm on the tracheal side of the carina (P < 0.01). When unilateral breath sounds were auscultated, the tube was located at 2.6 +/- 1.2 cm on the bronchial side of the carina. The tube was also located at 2.3 +/- 1.0 cm on the bronchial side of the carina when a unilateral shape of visualized breath sounds was obtained using the Visual Stethoscope (not significant).
  
  
  CONCLUSIONS
  During advancement of the tracheal tube, alterations of the shape of the visualized breath sounds using the Visual Stethoscope appeared before the changes of the breath sounds were detected by auscultation. Bilateral breath sounds disappeared when the tip of the tracheal tube was advanced beyond the carina in both groups.
authors.affiliation: Department of Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, Hamamatsu, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Kato
authors.forename: Akira
authors.initials: A
authors.lastname: Suzuki
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Makino
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Sanjo
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Nakai
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Shiraishi
authors.forename: Takasumi
authors.initials: T
authors.lastname: Katoh
authors.forename: Shigehito
authors.initials: S
authors.lastname: Sato
mesh_terms: D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D001314:Auscultation; D001980:Bronchi / Q000502:physiology*; D001999:Bronchoscopy; D015505:Chest Tubes; D004867:Equipment Design; D005260:Female; D005336:Fiber Optic Technology; D005583:Fourier Analysis; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012135:Respiratory Sounds; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D019023:Stethoscopes; D014132:Trachea / Q000502:physiology*; D014584:User-Computer Interface