title: The effects of airway pressure release ventilation on respiratory mechanics in extrapulmonary lung injury.
abstract: BACKGROUND
  Lung injury is often studied without consideration for pathologic changes in the chest wall. In order to reduce the incidence of lung injury using preemptive mechanical ventilation, it is important to recognize the influence of altered chest wall mechanics on disease pathogenesis. In this study, we hypothesize that airway pressure release ventilation (APRV) may be able to reduce the chest wall elastance associated with an extrapulmonary lung injury model as compared with low tidal volume (LVt) ventilation.
  
  
  METHODS
  Female Yorkshire pigs were anesthetized and instrumented. Fecal peritonitis was established, and the superior mesenteric artery was clamped for 30 min to induce an ischemia/reperfusion injury. Immediately following injury, pigs were randomized into (1) LVt (n = 3), positive end-expiratory pressure (PEEP) 5 cmH2O, V t 6 cc kg(-1), FiO2 21 %, and guided by the ARDSnet protocol or (2) APRV (n = 3), P High 16-22 cmH2O, P Low 0 cmH2O, T High 4.5 s, T Low set to terminate the peak expiratory flow at 75 %, and FiO2 21 %. Pigs were monitored continuously for 48 h. Lung samples and bronchoalveolar lavage fluid were collected at necropsy.
  
  
  RESULTS
  LVt resulted in mild acute respiratory distress syndrome (ARDS) (PaO2/FiO2 = 226.2 ± 17.1 mmHg) whereas APRV prevented ARDS (PaO2/FiO2 = 465.7 ± 66.5 mmHg; p < 0.05). LVt had a reduced surfactant protein A concentration and increased histologic injury as compared with APRV. The plateau pressure in APRV (34.3 ± 0.9 cmH2O) was significantly greater than LVt (22.2 ± 2.0 cmH2O; p < 0.05) yet transpulmonary pressure between groups was similar (p > 0.05). This was because the pleural pressure was significantly lower in LVt (7.6 ± 0.5 cmH2O) as compared with APRV (17.4 ± 3.5 cmH2O; p < 0.05). Finally, the elastance of the lung, chest wall, and respiratory system were all significantly greater in LVt as compared with APRV (all p < 0.05).
  
  
  CONCLUSIONS
  APRV preserved surfactant and lung architecture and maintenance of oxygenation. Despite the greater plateau pressure and tidal volumes in the APRV group, the transpulmonary pressure was similar to that of LVt. Thus, the majority of the plateau pressure in the APRV group was distributed as pleural pressure in this extrapulmonary lung injury model. APRV maintained a normal lung elastance and an open, homogeneously ventilated lung without increasing lung stress.
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. KolliscM@upstate.edu.
authors.forename: Michaela
authors.initials: M
authors.lastname: Kollisch-Singule
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. EmrB@upstate.edu.
authors.forename: Bryanna
authors.initials: B
authors.lastname: Emr
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. JainSu@upstate.edu.
authors.forename: Sumeet V
authors.initials: SV
authors.lastname: Jain
authors.affiliation: Department of Trauma Critical Care Medicine, R Adams Cowley Shock Trauma Center, University of Maryland School of Medicine, Baltimore, MD, USA. plandrews@intensivecareonline.com.
authors.forename: Penny
authors.initials: P
authors.lastname: Andrews
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. satalinj@upstate.edu.
authors.forename: Joshua
authors.initials: J
authors.lastname: Satalin
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. catherine015@163.com.
authors.forename: Jiao
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. PorcellE@upstate.edu.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Porcellio
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. KenyonV@upstate.edu.
authors.forename: Van
authors.initials: V
authors.lastname: Kenyon
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. WangG@upstate.edu.
authors.forename: Guirong
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. MarxW@upstate.edu.
authors.forename: William
authors.initials: W
authors.lastname: Marx
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. Louis.Gatto@cortland.edu.|Department of Biological Sciences, SUNY Cortland, Cortland, NY, USA. Louis.Gatto@cortland.edu.
authors.forename: Louis A
authors.initials: LA
authors.lastname: Gatto
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY, 13210, USA. NiemanG@upstate.edu.
authors.forename: Gary F
authors.initials: GF
authors.lastname: Nieman
authors.affiliation: Department of Trauma Critical Care Medicine, R Adams Cowley Shock Trauma Center, University of Maryland School of Medicine, Baltimore, MD, USA. nmh@xmxmail.com.
authors.forename: Nader M
authors.initials: NM
authors.lastname: Habashi
keywords: Airway pressure release ventilation (APRV); Chest wall elastance; Low tidal volume ventilation; Lung injury; Transpulmonary pressure