title: A method for determining optimal mean airway pressure in high-frequency oscillatory ventilation.
abstract: BACKGROUND
  "Optimal" mean airway pressure (MAP) during high-frequency oscillatory ventilation (HFOV) can be defined as the pressure that allows for maximal alveolar recruitment while minimizing alveolar overdistension. Choosing a MAP near or just below the point of maximal curvature (PMC) of the volume-pressure characteristics of the lung can serve as a guide to avoid overdistention during HFOV, while simultaneously preventing derecruitment. The purpose of this study was to assess whether optimal MAP at the PMC can be determined by using measures of PaO(2) in patients with acute respiratory distress syndrome (ARDS) undergoing HFOV.
  
  
  METHODS
  We prospectively studied seven patients with ARDS who underwent HFOV after failed conventional ventilation. In addition, 11 healthy subjects were studied to validate measurements of changes in end-expiratory lung volume (∆EELV) using magnetometers. Using this validated method, plots of ∆EELV and MAP were constructed during decremental changes in MAP following a recruitment maneuver in seven ventilated patients with ARDS. The PMC was defined as the point where the slope of the ∆EELV versus MAP curve acutely changed. The MAP at the PMC was compared to that determined from plots of PaO(2) versus MAP.
  
  
  RESULTS
  In the healthy cohort, measurements of ∆EELV obtained by magnetometry approximated the line of identity when compared to those obtained by spirometry. The MAP determined using either the ∆EELV or PaO(2) techniques were identical in all seven HFOV ventilated patients. Additionally, there was a significant correlation between the MAP associated changes in PaO2 and the MAP associated changes in ∆EELV (p < 0.001).
  
  
  CONCLUSIONS
  The finding that MAP at the PMC is the same whether determined by measures of ∆EELV or PaO(2) suggest that bedside measures PaO(2) may provide an acceptable surrogate for measures of EELV when determining "optimal" MAP during HFOV.
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, The Memorial Hospital of Rhode Island, Pawtucket, RI, USA. brian_casserly@brown.edu
authors.forename: Brian
authors.initials: B
authors.lastname: Casserly
authors.forename: F
authors.initials: F
authors.lastname: Dennis McCool
authors.forename: Jigme M
authors.initials: JM
authors.lastname: Sethi
authors.forename: Eyad
authors.initials: E
authors.lastname: Kawar
authors.forename: Richard
authors.initials: R
authors.lastname: Read
authors.forename: Mitchell M
authors.initials: MM
authors.lastname: Levy
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006612:High-Frequency Ventilation; D006801:Humans; D008168:Lung / Q000378:metabolism / Q000503:physiopathology*; D008176:Lung Volume Measurements; D060306:Magnetometry / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D015656:Respiratory Mechanics / Q000502:physiology*; D013147:Spirometry / Q000379:methods
chemical_list: D010100:Oxygen