title: Validation study of two-microphone acoustic reflectometry for determination of breathing tube placement in 200 adult patients.
abstract: BACKGROUND
  Acoustic reflectometry allows the construction of a one-dimensional image of a cavity, such as the airway or the esophagus. The reflectometric area-distance profile consists of a constant cross-sectional area segment (length of endotracheal tube), followed either by a rapid increase in the area beyond the carina (tracheal intubation) or by an immediate decrease in the area (esophageal intubation).
  
  
  METHODS
  Two hundred adult patients were induced and intubated, without restrictions on anesthetic agents or airway adjunct devices. A two-microphone acoustic reflectometer was used to determine whether the breathing tube was placed in the trachea or esophagus. A blinded reflectometer operator, seated a distance away from the patient, interpreted the acoustic area-distance profile alone to decide where the tube was placed. Capnography was used as the gold standard.
  
  
  RESULTS
  Of 200 tracheal intubations confirmed by capnography, the reflectometer operator correctly identified 198 (99% correct tracheal intubation identification rate). In two patients there were false-negative results, patients with a tracheal intubation were interpreted as having an esophageal intubation. A total of 14 esophageal intubations resulted, all correctly identified by reflectometry, for a 100% esophageal intubation identification rate.
  
  
  CONCLUSIONS
  Acoustic reflectometry is a rapid, noninvasive method by which to determine whether breathing tube placement is correct (tracheal) or incorrect (esophageal). Reflectometry determination of tube placement may be useful in airway emergencies, particularly in cases where visualization of the glottic area is not possible and capnography may fail, as in patients with cardiac arrest.
authors.affiliation: Department of Anesthesiology, Room 14-901, Keck School of Medicine, University of Southern California, 1200 North State Street, Los Angeles, CA 90033, USA. draphael@usc.edu
authors.forename: David T
authors.initials: DT
authors.lastname: Raphael
authors.forename: Maxim
authors.initials: M
authors.lastname: Benbassat
authors.forename: Dimiter
authors.initials: D
authors.lastname: Arnaudov
authors.forename: Alex
authors.initials: A
authors.lastname: Bohorquez
authors.forename: Bita
authors.initials: B
authors.lastname: Nasseri
mesh_terms: D000162:Acoustics; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019296:Capnography; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results