title: Utilization of the lower inflection point of the pressure-volume curve results in protective conventional ventilation comparable to high frequency oscillatory ventilation in an animal model of acute respiratory distress syndrome.
abstract: BACKGROUND
  Studies comparing high frequency oscillatory and conventional ventilation in acute respiratory distress syndrome have used low values of positive end-expiratory pressure and identified a need for better recruitment and pulmonary stability with high frequency.
  
  
  OBJECTIVE
  To compare conventional and high frequency ventilation using the lower inflection point of the pressure-volume curve as the determinant of positive end-expiratory pressure to obtain similar levels of recruitment and alveolar stability.
  
  
  METHODS
  After lung lavage of adult rabbits and lower inflection point determination, two groups were randomized: conventional (positive end-expiratory pressure = lower inflection point; tidal volume=6 ml/kg) and high frequency ventilation (mean airway pressures= lower inflection point +4 cmH2O). Blood gas and hemodynamic data were recorded over 4 h. After sacrifice, protein analysis from lung lavage and histologic evaluation were performed.
  
  
  RESULTS
  The oxygenation parameters, protein and histological data were similar, except for the fact that significantly more normal alveoli were observed upon protective ventilation. High frequency ventilation led to lower PaCO2 levels.
  
  
  CONCLUSIONS
  Determination of the lower inflection point of the pressure-volume curve is important for setting the minimum end expiratory pressure needed to keep the airways opened. This is useful when comparing different strategies to treat severe respiratory insufficiency, optimizing conventional ventilation, improving oxygenation and reducing lung injury.
  
  
  CONCLUSIONS
  Utilization of the lower inflection point of the pressure-volume curve in the ventilation strategies considered in this study resulted in comparable efficacy with regards to oxygenation and hemodynamics, a high PaCO2 level and a lower pH. In addition, a greater number of normal alveoli were found after protective conventional ventilation in an animal model of acute respiratory distress syndrome.
authors.affiliation: Experimental Research Unit (LIM 30), Department of Pediatrics, Medical School, São Paulo University, São Paulo, SP, Brazil.
authors.forename: Felipe S
authors.initials: FS
authors.lastname: Rossi
authors.forename: Renata Suman
authors.initials: RS
authors.lastname: Mascaretti
authors.forename: Luciana B
authors.initials: LB
authors.lastname: Haddad
authors.forename: Norberto A
authors.initials: NA
authors.lastname: Freddi
authors.forename: Thais
authors.initials: T
authors.lastname: Mauad
authors.forename: Celso M
authors.initials: CM
authors.lastname: Rebello
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001784:Blood Gas Analysis; D018893:Bronchoalveolar Lavage; D016009:Chi-Square Distribution; D004195:Disease Models, Animal; D006612:High-Frequency Ventilation / Q000009:adverse effects; D008168:Lung / Q000473:pathology; D008170:Lung Compliance; D011175:Positive-Pressure Respiration / Q000009:adverse effects / Q000379:methods*; D011817:Rabbits; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000473:pathology / Q000503:physiopathology / Q000628:therapy; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors