title: Correlation of lung collapse and gas exchange - a computer tomographic study in sheep and pigs with atelectasis in otherwise normal lungs.
abstract: BACKGROUND
  Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations.
  
  
  METHODS
  Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range).
  
  
  RESULTS
  Mtotal was 768 (715-884) g in sheep and 543 (503-583) g in pigs. Atelectasis was 26 (16-47) % in sheep and 18 (13-23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106-414) mmHg in sheep and 480 (437-514) mmHg in pigs. Shunt was 39 (29-51) % in sheep and 15 (11-20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt.
  
  
  CONCLUSIONS
  In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Wolf
authors.affiliation: Anaesthesiology and Intensive Care Medicine, Fachkrankenhaus Coswig, Coswig/Meißen, Germany.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Reske
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Sören
authors.initials: S
authors.lastname: Hammermüller
authors.affiliation: Cardio-Pulmonary Department, Pulmonary Division, Hospital das Clínicas, University of São Paulo, São Paulo, Brazil; Research and Education Institute, Hospital Sírio Libanês, São Paulo, Brazil.
authors.forename: Eduardo L V
authors.initials: EL
authors.lastname: Costa
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital Carl Gustav Carus, Dresden, Germany.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Spieth
authors.affiliation: Department of Orthopedic, Trauma and Plastic Surgery, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Pierre
authors.initials: P
authors.lastname: Hepp
authors.affiliation: Carlos Chagas Biophysics Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Alysson R
authors.initials: AR
authors.lastname: Carvalho
authors.affiliation: Anaesthesiology and Intensive Care Medicine, Fachkrankenhaus Coswig, Coswig/Meißen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Kraßler
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Hermann
authors.initials: H
authors.lastname: Wrigge
authors.affiliation: Cardio-Pulmonary Department, Pulmonary Division, Hospital das Clínicas, University of São Paulo, São Paulo, Brazil.
authors.forename: Marcelo B P
authors.initials: MB
authors.lastname: Amato
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.
authors.forename: Andreas W
authors.initials: AW
authors.lastname: Reske
mesh_terms: D000768:Anesthesia, General; D000818:Animals; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D010313:Partial Pressure; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D012756:Sheep; D013045:Species Specificity; D013552:Swine; D014057:Tomography, X-Ray Computed; D014661:Vasoconstriction