title: Removal of the tracheal tube after prolonged mechanical ventilation: assessment of risk by oscillatory impedance.
abstract: BACKGROUND
  Decannulation failure is usually due to tracheal obstruction. Prior to decannulation, inspection by the invasive procedure of bronchoscopy that permits morphological evaluation of a tracheal stenosis is standard practice. A non-invasive method enabling the quantification of the airway obstruction that requires little cooperation is measurement of the airway resistance by the forced oscillation technique.
  
  
  OBJECTIVE
  The aim of the present study was to define oscillatory impedance thresholds which predict successful decannulation.
  
  
  METHODS
  A total of 131 patients were investigated prospectively. Step 1: Following probatory decannulation, measurement of the oscillatory impedance. Step 2: Blinded to the results of the impedance measurement, bronchoscopy-assisted decannulation attempt. The criteria for renewed cannulation were high-grade laryngeal or tracheal obstruction, dyspnea or stridor, or a drop in SaO(2) <90% under O(2) insufflation.
  
  
  METHODS
  Determination of the ratio tracheal tube remains/tracheal tube removed (TT+/TT-) for every measured value of the oscillatory resistance at 5 Hz (Ros 5 Hz). Determination of specificity and positive predictive value for determined threshold values with respect to TT-.
  
  
  RESULTS
  The data of 126 patients were evaluated. TT+ n = 26, TT- n = 100. Decannulation on the basis of bronchoscopy criteria: Specificity and positive predictive value found out for Ros 5 Hz <0.35 kPa/l/s (n = 44) were 1.00 and 1.00, respectively, and for Ros 5 Hz <0.47 kPa/l/s (n = 71) 0.88 and 0.96, respectively.
  
  
  CONCLUSIONS
  Measurement of the oscillatory airway resistance represents a practicable method prior to decannulation. Below a value of Ros 5 Hz <0.35 kPa/l/s, bronchoscopy would appear not to be necessary.
authors.affiliation: Department of Pneumology and Critical Care Medicine, Helios Klinik Ambrock, University of Witten/Herdecke, Hagen, Germany. karl-josef.franke@helios-kliniken.de
authors.forename: Karl-Josef
authors.initials: KJ
authors.lastname: Franke
authors.forename: Georg
authors.initials: G
authors.lastname: Nilius
authors.forename: Stefan
authors.initials: S
authors.lastname: Morgenstern
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Ruhle
mesh_terms: D000368:Aged; D000403:Airway Resistance; D001999:Bronchoscopy; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009991:Oscillometry; D011446:Prospective Studies; D014135:Tracheal Stenosis / Q000175:diagnosis* / Q000209:etiology; D015300:Ventilator Weaning