title: Following tracheal intubation, mucus flow is reversed in the semirecumbent position: possible role in the pathogenesis of ventilator-associated pneumonia.
abstract: OBJECTIVE
  Critically ill intubated patients are positioned in the semirecumbent position to prevent pneumonia. In tracheally intubated sheep, we investigated the effects of gravitational force on tracheal mucus transport and on bacterial colonization of the respiratory system.
  
  
  METHODS
  Prospective randomized animal study.
  
  
  METHODS
  Animal research facility at the National Institutes of Health.
  
  
  METHODS
  Sixteen healthy sheep.
  
  
  METHODS
  Spontaneously breathing or mechanically ventilated sheep were randomized to be positioned with the orientation of the trachea above (40 degrees, trachea-up) or below (5 degrees, trachea-down) horizontal.
  
  
  RESULTS
  Tracheal mucus velocity was measured through radiographic tracking of radiopaque tantalum disks, insufflated into the trachea. After 24 hrs, sheep were euthanized, and samples from the airways and lungs were taken for microbiological analysis. The proximal trachea was colonized in all sheep. In trachea-down sheep, all mucus moved toward the glottis at a mean velocity of 2.1 +/- 1.1 mm/min. When mucus reached the endotracheal tube, it either entered the endotracheal tube or was lodged at the inflated endotracheal tube cuff. In all trachea-up sheep, abnormal tracheal mucus clearance was found. Mucus, mostly on the nondependent part of the trachea, moved toward the glottis at an average velocity of 2.2 +/- 2.0 mm/min and constantly accumulated at the inflated endotracheal tube cuff. From the proximal trachea, mucus eventually moved toward the lungs on the dependent part of the trachea, leading to an "intratracheal route" of colonization of the lungs. Pneumonia was found in 6/8 of trachea-up sheep and the same microorganisms were isolated from the lungs and the proximal trachea. No pneumonia was found in trachea-down sheep (p = .007).
  
  
  CONCLUSIONS
  The study indicates that following tracheal intubation gravitational force influences tracheal mucus clearance. When the trachea is oriented above horizontal, a flow of mucus from the proximal trachea toward the lungs is highly associated with bacterial colonization of the airways and pneumonia.
authors.affiliation: Pulmonary and Critical Care Medicine Branch, Section of Pulmonary and Cardiac Assist Devices, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA. libassig@aim.com
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Li Bassi
authors.forename: Alberto
authors.initials: A
authors.lastname: Zanella
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Mario
authors.initials: M
authors.lastname: Stylianou
authors.forename: Theodor
authors.initials: T
authors.lastname: Kolobow
mesh_terms: D000818:Animals; D015169:Colony Count, Microbial; D005260:Female; D006112:Gravitation; D007442:Intubation, Intratracheal / Q000295:instrumentation; D009079:Mucociliary Clearance / Q000502:physiology*; D009093:Mucus; D053717:Pneumonia, Ventilator-Associated / Q000209:etiology*; D011187:Posture; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D012212:Rheology; D012756:Sheep