title: Effect of rate and inspiratory flow on ventilator-induced lung injury.
abstract: BACKGROUND
  We examined the effects of decreasing respiratory rate (RR) at variable inspiratory times (It) and reducing inspiratory flow on the development of ventilator-induced lung injury.
  
  
  METHODS
  Forty sheep weighing 24.6+/-3.2 kg were ventilated for 6 hours with one of five strategies (FIO2 = 1.0, positive end-expiratory pressure = 5 cm H2O): (1) pressure-controlled ventilation (PCV), RR = 15 breaths/min, peak inspiratory pressure (PIP) = 25 cm H2O, n = 8; (2) PCV, RR = 15 breaths/min, PIP = 50 cm H2O, n = 8; (3) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 6 seconds, n = 8; (4) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 2 seconds, n = 8; and (5) limited inspiratory flow volume-controlled ventilation, RR = 5 breaths/min, pressure-limit = 50 cm H2O, flow = 15 L/min, n = 8.
  
  
  RESULTS
  Decreasing RR at conventional flows did not reduce injury. However, limiting inspiratory flow rate (LIFR) maintained compliance and resulted in lower Qs/Qt (HiPIP = 38+/-18%, LIFR = 19+/-6%, p < 0.001), reduced histologic injury (HiPIP = 14+/-0.9, LIFR = 2.2+/-0.9, p < 0.05), decreased intra-alveolar neutrophils (HiPIP = 90+/-49, LIFR = 7.6+/-3.8,p = 0.001), and reduced wet-dry lung weight (HiPIP = 87.3+/-8.5%, LIFR = 40.8+/-17.4%,p < 0.001).
  
  
  CONCLUSIONS
  High-pressure ventilation for 6 hours using conventional flow patterns produces severe lung injury, irrespective of RR or It. Reduction of inspiratory flow at similar PIP provides pulmonary protection.
authors.affiliation: Department of Surgery, University of Michigan Medical Center, Ann Arbor, USA.
authors.forename: P B
authors.initials: PB
authors.lastname: Rich
authors.forename: C A
authors.initials: CA
authors.lastname: Reickert
authors.forename: S
authors.initials: S
authors.lastname: Sawada
authors.forename: S S
authors.initials: SS
authors.lastname: Awad
authors.forename: W R
authors.initials: WR
authors.lastname: Lynch
authors.forename: K J
authors.initials: KJ
authors.lastname: Johnson
authors.forename: R B
authors.initials: RB
authors.lastname: Hirschl
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D006439:Hemodynamics; D007320:Inspiratory Capacity; D007958:Leukocyte Count; D008170:Lung Compliance; D009504:Neutrophils / Q000473:pathology; D009929:Organ Size; D011175:Positive-Pressure Respiration / Q000379:methods*; D012119:Respiration; D012121:Respiration, Artificial / Q000009:adverse effects*; D012128:Respiratory Distress Syndrome / Q000145:classification / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D012756:Sheep; D013997:Time Factors