title: Lung recruitment during small tidal volume ventilation allows minimal positive end-expiratory pressure without augmenting lung injury.
abstract: OBJECTIVE
  Ventilation with positive end-expiratory pressure (PEEP) above the inflection point (P(inf)) has been shown to reduce lung injury by recruiting previously closed alveolar regions; however, it carries the risk of hyperinflating the lungs. The present study examined the hypothesis that a new strategy of recruiting the lung with a sustained inflation (SI), followed by ventilation with small tidal volumes, would allow the maintenance of low PEEP levels (<P(inf)) without inducing additional lung injury.
  
  
  METHODS
  Prospective, randomized, controlled ex vivo study.
  
  
  METHODS
  An animal laboratory in a university setting.
  
  
  METHODS
  Isolated nonperfused lungs of adult Sprague-Dawley rats.
  
  
  METHODS
  We studied the effect on compliance and lung injury in four groups (n = 10 per group) of lavaged rat lungs. One group (group 1) served as a control; their lungs were inflated at PEEP < P(inf) but not ventilated. The other three groups were ventilated with small tidal volumes (5 to 6 mL/kg) for 2 hrs with the following interventions: group 2, PEEP < P(inf) without SI; group 3, PEEP < P(inf) after a SI to 30 cm H2O for 30 secs; and group 4, PEEP > P(inf).
  
  
  RESULTS
  In groups 2 and 4, static compliance decreased after ventilation (p < .01). Histologically, group 2 (PEEP < P(inf) without SI) showed significantly greater injury of small airways, but not of terminal respiratory units, compared with group 1. Group 3 (PEEP < P(inf) after a SI), but not group 4, showed significantly less injury of small airways and terminal respiratory units compared with group 2.
  
  
  CONCLUSIONS
  We conclude that small tidal volume ventilation after a recruitment maneuver allows ventilation on the deflation limb of the pressure/volume curve of the lungs at a PEEP < P(inf). This strategy a) minimizes lung injury as well as, or better than, use of PEEP > P(inf), and b) ensures a lower PEEP, which may minimize the detrimental consequences of high lung volume ventilation.
authors.affiliation: Department of Critical Care, The Hospital for Sick Children, University of Toronto, Ontario, Canada. peter.rimensberger@hcuge.ch
authors.forename: P C
authors.initials: PC
authors.lastname: Rimensberger
authors.forename: G
authors.initials: G
authors.lastname: Pristine
authors.forename: B M
authors.initials: BM
authors.lastname: Mullen
authors.forename: P N
authors.initials: PN
authors.lastname: Cox
authors.forename: A S
authors.initials: AS
authors.lastname: Slutsky
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D007327:Insufflation; D007385:Intermittent Positive-Pressure Ventilation / Q000379:methods*; D008170:Lung Compliance; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012128:Respiratory Distress Syndrome / Q000473:pathology / Q000628:therapy*; D015656:Respiratory Mechanics; D014109:Total Lung Capacity