title: Lung and 'end organ' injury due to mechanical ventilation in animals: comparison between the prone and supine positions.
abstract: BACKGROUND
  Use of the prone position in patients with acute lung injury improves their oxygenation. Most of these patients die from multisystem organ failure and not from hypoxia, however. Moreover, there is some evidence that the organ failure is caused by increased cell apoptosis. In the present study we therefore examined whether the position of the patients affects histological changes and apoptosis in the lung and 'end organs', including the brain, heart, diaphragm, liver, kidneys and small intestine.
  
  
  METHODS
  Ten mechanically ventilated sheep with a tidal volume of 15 ml/kg body weight were studied for 90 minutes. Five sheep were placed in the supine position and five sheep were placed in the prone position during the experiment. Lung changes were analyzed histologically using a semiquantitative scoring system and the extent of apoptosis was investigated with the TUNEL method.
  
  
  RESULTS
  In the supine position intra-alveolar hemorrhage appeared predominantly in the dorsal areas, while the other histopathologic lesions were homogeneously distributed throughout the lungs. In the prone position, all histological changes were homogeneously distributed. A significantly higher score of lung injury was found in the supine position than in the prone position (4.63 +/- 0.58 and 2.17 +/- 0.19, respectively) (P < 0.0001). The histopathologic changes were accompanied by increased apoptosis (TUNEL method). In the supine position, the apoptotic index in the lung and in most of the 'end organs' was significantly higher compared with the prone position (all P < 0.005). Interestingly, the apoptotic index was higher in dorsal areas compared with ventral areas in both the prone and supine positions (P < 0.003 and P < 0.02, respectively).
  
  
  CONCLUSIONS
  Our results suggest that the prone position appears to reduce the severity and the extent of lung injury, and is associated with decreased apoptosis in the lung and 'end organs'.
authors.affiliation: Department of Intensive Care Unit, University Hospital of Ioannina, Greece. gnakos@cc.uoi.gr
authors.forename: George
authors.initials: G
authors.lastname: Nakos
authors.forename: Anna
authors.initials: A
authors.lastname: Batistatou
authors.forename: Eftychia
authors.initials: E
authors.lastname: Galiatsou
authors.forename: Eleonora
authors.initials: E
authors.lastname: Konstanti
authors.forename: Vassilios
authors.initials: V
authors.lastname: Koulouras
authors.forename: Panayotis
authors.initials: P
authors.lastname: Kanavaros
authors.forename: Apostolos
authors.initials: A
authors.lastname: Doulis
authors.forename: Athanassios
authors.initials: A
authors.lastname: Kitsakos
authors.forename: Angeliki
authors.initials: A
authors.lastname: Karachaliou
authors.forename: Marilena E
authors.initials: ME
authors.lastname: Lekka
authors.forename: Maria
authors.initials: M
authors.lastname: Bai
mesh_terms: D000818:Animals; D008168:Lung / Q000473:pathology* / Q000502:physiology; D009102:Multiple Organ Failure / Q000209:etiology / Q000473:pathology / Q000628:therapy; D016684:Prone Position / Q000502:physiology*; D012121:Respiration, Artificial / Q000009:adverse effects* / Q000379:methods; D012128:Respiratory Distress Syndrome / Q000209:etiology / Q000473:pathology* / Q000628:therapy; D012756:Sheep; D016683:Supine Position / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology