title: Positive end-expiratory pressure above lower inflection point minimizes influx of activated neutrophils into lung.
abstract: OBJECTIVE
  To compare the effects of low vs. high tidal volume (Vt) with three positive end-expiratory pressure (PEEP) strategies on activated neutrophil influx into the lung.
  
  
  METHODS
  Prospective, randomized controlled animal study.
  
  
  METHODS
  Animal laboratory in a university hospital.
  
  
  METHODS
  Newborn piglets.
  
  
  METHODS
  Surfactant-depleted piglets were randomized in littermate pairs; to PEEP of either 0 (zero end-expiratory pressure [ZEEP]; n = 6), 8 cm H2O (PEEP 8; n = 5), or 1 cm H2O above the lower inflection point (LIP) (PEEP>LIP; n = 6). Within each pair piglets were randomized to a low VT (5-7 mL/kg) or high VT strategy (17-19 mL/kg). After 4 hrs of mechanical ventilation, 18-fluorodeoxyglucose (18FDG) was injected and positron emission tomography scanning was performed.
  
  
  RESULTS
  VT and PEEP changes on influx constants of 18FDG were assessed by analysis of variance. A within-litter comparison of Vt was nonsignificant (p = .50). A between-litter comparison, ordered in linear trend rank, from ZEEP, to PEEP 8, to PEEP>LIP, showed a strong effect of PEEP on influx constant (p = .019).
  
  
  CONCLUSIONS
  PEEP set above the LIP on the inspiratory limb of the pressure-volume curve affords a stronger lung protection than VT strategy.
authors.affiliation: Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Monkman
authors.forename: Chad C
authors.initials: CC
authors.lastname: Andersen
authors.forename: Claude
authors.initials: C
authors.lastname: Nahmias
authors.forename: Hasan
authors.initials: H
authors.lastname: Ghaffer
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Bourgeois
authors.forename: Robin S
authors.initials: RS
authors.lastname: Roberts
authors.forename: Barbara
authors.initials: B
authors.lastname: Schmidt
authors.forename: Haresh M
authors.initials: HM
authors.lastname: Kirpalani
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001707:Biopsy, Needle; D002465:Cell Movement; D004195:Disease Models, Animal; D005260:Female; D007150:Immunohistochemistry; D008170:Lung Compliance; D008297:Male; D009504:Neutrophils / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000379:methods*; D049268:Positron-Emission Tomography; D011336:Probability; D012123:Pulmonary Ventilation; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy*; D012680:Sensitivity and Specificity; D013990:Tidal Volume