title: Lung computed tomography density distribution in a porcine model of one-lung ventilation.
abstract: BACKGROUND
  One-lung ventilation (OLV) exposes the dependent lung to increased mechanical stress which may affect the postoperative course. This study evaluates regional pulmonary gas/tissue distribution in a porcine model of OLV.
  
  
  METHODS
  Nine anaesthetized and mechanically ventilated (V(T)=10 ml kg(-1), FI(O(2))=0.40, PEEP=5 cm H(2)O) pigs were studied. After lung separation by an endobronchial blocker, lateral thoracotomy and OLV were performed in six pigs. Three animals served as controls. Static end-expiratory and end-inspiratory spiral computed tomography (CT) scans were done before, during, and after OLV and at corresponding times in controls. CT images were analysed by defined regions of interest and summarized voxels were classified by defined lung X-ray density intervals (atelectasis, poorly aerated, normally aerated, and overaerated).
  
  
  RESULTS
  Dependent lungs contained poorly aerated regions and atelectasis with a significant tidal recruitment during conventional two-lung ventilation (TLV) before OLV (expiration vs inspiration: atelectasis 29% vs 14%; poorly aerated 66% vs 44%; normally aerated 4% vs 41% of the dependent lung volume, P<0.05). During OLV (V(T)=10 ml kg(-1)), cyclic recruitment was increased. The density spectrum of the ventilated lung changed from consolidation to aeration (expiration vs inspiration: atelectasis 10% vs 2%; poorly aerated 71% vs 18%; normally aerated 19% vs 79%, P<0.05). After OLV, increased aeration remained with less atelectasis and poorly aerated regions. Lung density distribution in the non-dependent lung of OLV pigs was unaltered after the period of complete lung collapse.
  
  
  CONCLUSIONS
  Cyclic tidal recruitment during OLV in pigs was associated with a persistent increase of aeration in the dependent lung.
authors.affiliation: Department of Medical Sciences, Clinical Physiology, Uppsala University, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Kozian
authors.forename: T
authors.initials: T
authors.lastname: Schilling
authors.forename: H
authors.initials: H
authors.lastname: Schütze
authors.forename: F
authors.initials: F
authors.lastname: Heres
authors.forename: T
authors.initials: T
authors.lastname: Hachenberg
authors.forename: G
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D000818:Animals; D006439:Hemodynamics / Q000502:physiology; D008168:Lung / Q000000981:diagnostic imaging* / Q000502:physiology; D008176:Lung Volume Measurements; D023421:Models, Animal; D011175:Positive-Pressure Respiration / Q000379:methods*; D001261:Pulmonary Atelectasis / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D034421:Sus scrofa; D013908:Thoracotomy; D013990:Tidal Volume / Q000502:physiology; D014057:Tomography, X-Ray Computed