title: Maximal hysteresis: a new method to set positive end-expiratory pressure in acute lung injury?
abstract: BACKGROUND
  No methods are superior when setting positive end-expiratory pressure (PEEP) in acute lung injury (ALI). In ALI, the vertical distance (hysteresis) between the inspiratory and expiratory limbs of a static pressure-volume (PV) loop mainly indicates lung recruitment. We hypothesized that PEEP set at the pressure where hysteresis is 90% of its maximum (90%MH) would give similar oxygenation, but less cardiovascular depression than PEEP set at the pressure at lower inflection point (LIP) on the inspiratory limb or at the point of maximal curvature (PMC) on the expiratory limb in ALI.
  
  
  METHODS
  In 12 mechanically ventilated pigs, ALI was induced in a randomized fashion by lung lavage, lung lavage plus injurious ventilation, or by oleic acid. From a static PV loop obtained by an interrupted low-flow method, the pressures at LIP [25 (25, 25) cmH(2)O, mean and 25, 75 percentiles], at PMC [24 (20, 24) cmH(2)O], and at 90% MH [19 (18, 19) cmH(2)O] were determined and used for the PEEP-settings. We measured lung inflation (by computed tomography), end-expiratory lung volume (EELV), airway pressures, compliance of the respiratory system (Crs), blood gases, cardiac output and arterial blood pressure.
  
  
  RESULTS
  There were no differences between the PEEP settings in EELV or oxygenation, but the 90%MH setting gave lower end-inspiratory pause pressure (P<0.025), higher Crs (P<0.025), less hyper-aeration (P<0.025) and better maintained hemodynamics.
  
  
  CONCLUSIONS
  In this porcine lung injury model, PEEP set at 90% MH gave better lung mechanics and hemodynamics, than PEEP set at PMC or LIP.
authors.affiliation: Clinical Institute, Aarhus University Hospital, Skejby, Denmark. koefoed-nielsen@ki.au.dk
authors.forename: J
authors.initials: J
authors.lastname: Koefoed-Nielsen
authors.forename: G
authors.initials: G
authors.lastname: Andersen
authors.forename: A
authors.initials: A
authors.lastname: Barklin
authors.forename: A
authors.initials: A
authors.lastname: Bach
authors.forename: S
authors.initials: S
authors.lastname: Lunde
authors.forename: E
authors.initials: E
authors.lastname: Tønnesen
authors.forename: A
authors.initials: A
authors.lastname: Larsson
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D011175:Positive-Pressure Respiration / Q000379:methods*; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000139:chemically induced / Q000473:pathology / Q000628:therapy*; D012129:Respiratory Function Tests / Q000706:statistics & numerical data; D013552:Swine; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome