title: Gravity predominates over ventilatory pattern in the prevention of ventilator-associated pneumonia.
abstract: OBJECTIVE
  In the semirecumbent position, gravity-dependent dissemination of pathogens has been implicated in the pathogenesis of ventilator-associated pneumonia. We compared the preventive effects of a ventilatory strategy, aimed at decreasing pulmonary aspiration and enhancing mucus clearance versus the Trendelenburg position.
  
  
  METHODS
  Prospective randomized animal study.
  
  
  METHODS
  Animal research facility, University of Barcelona, Spain.
  
  
  METHODS
  Twenty-four Large White-Landrace pigs.
  
  
  METHODS
  Pigs were intubated and on mechanical ventilation for 72 hours. Following surgical preparation, pigs were randomized to be positioned: 1) in semirecumbent/prone position, ventilated with a duty cycle (TITTOT) of 0.33 and without positive end-expiratory pressure (control); 2) as in the control group, positive end-expiratory pressure of 5 cm H2O and TITTOT to achieve a mean expiratory-inspiratory flow bias of 10 L/min (treatment); 3) in Trendelenburg/prone position and ventilated as in the control group (Trendelenburg). Following randomization, Pseudomonas aeruginosa was instilled into the oropharynx.
  
  
  RESULTS
  Mucus clearance rate was measured through fluoroscopic tracking of tracheal markers. Microspheres were instilled into the subglottic trachea to assess pulmonary aspiration. Ventilator-associated pneumonia was confirmed by histological/microbiological studies. The mean expiratory-inspiratory flow in the treatment, control, and Trendelenburg groups were 10.7 ± 1.7, 1.8 ± 3.7 and 4.3 ± 2.8 L/min, respectively (p < 0.001). Mucus clearance rate was 11.3 ± 9.9 mm/min in the Trendelenburg group versus 0.1 ± 1.0 in the control and 0.2 ± 1.0 in the treatment groups (p = 0.002). In the control group, we recovered 1.35% ± 1.24% of the instilled microspheres per gram of tracheal secretions, whereas 0.22% ± 0.25% and 0.97% ± 1.44% were recovered in the treatment and Trendelenburg groups, respectively (p = 0.031). Ventilator-associated pneumonia developed in 66.67%, 85.71%, and 0% of the animals in the control, treatment, and Trendelenburg groups (p < 0.001).
  
  
  CONCLUSIONS
  The Trendelenburg position predominates over expiratory flow bias and positive end-expiratory pressure in the prevention of gravity-dependent translocation of oropharyngeal pathogens and development of ventilator-associated pneumonia. These findings further substantiate the primary role of gravity in the pathogenesis of ventilator-associated pneumonia.
authors: 1Department of Pulmonary and Critical Care Medicine, Division of Animal Experimentation, Hospital Clínic, Thorax Institute, Barcelona, Spain. 2Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain. 3Centro de Investigación Biomedica En Red-Enfermedades Respiratorias, Barcelona, Spain. 4Department of Cardiology, Hospital Clínic, Thorax Institute, Barcelona, Spain. 5Department of Clinical Microbiology, School of Medicine, and Barcelona Centre for International Health Research (CRESIB, Hospital Clínic, Universitat de Barcelona), Barcelona, Spain. 6Department of Pathology, Hospital Clínic, Barcelona, Spain. 7Pulmonary Intensive Care Unit, Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil. 8Department of Pneumology, Hospital Clínic, Thorax Institute, Office of Biostatistics, Barcelona, Spain. 9University of Barcelona, Barcelona, Spain.
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mesh_terms: D000818:Animals; D006112:Gravitation; D006439:Hemodynamics; D009093:Mucus / Q000502:physiology; D053717:Pneumonia, Ventilator-Associated / Q000382:microbiology* / Q000517:prevention & control*; D011175:Positive-Pressure Respiration; D016684:Prone Position; D011446:Prospective Studies; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa; D011897:Random Allocation; D012121:Respiration, Artificial / Q000379:methods*; D013552:Swine; D014132:Trachea / Q000502:physiology