title: Hints for cyclical recruitment of atelectasis during ongoing mechanical ventilation in lavage and oleic acid lung injury detected by SpO₂ oscillations and electrical impedance tomography.
abstract: OBJECTIVE
  Detection of cyclical recruitment of atelectasis after induction of lavage (LAV) or oleic acid injury (OAI) in mechanically ventilated pigs. Primary hypothesis is that oxygen oscillations within the respiratory cycle can be detected by SpO₂ recordings (direct hint). SpO₂ oscillations reflect shunt oscillations that can only be explained by cyclical recruitment of atelectasis. Secondary hypothesis is that electrical impedance tomography (EIT) depicts specific regional changes of lung aeration and of pulmonary mechanical properties (indirect hint).
  
  
  METHODS
  Three groups (each n = 7) of mechanically ventilated pigs were investigated applying above mentioned methods before and repeatedly after induction of lung injury: (1) sham treated animals (SHAM), (2) LAV, and (3) OAI.
  
  
  RESULTS
  Early oxygen oscillations occurred in the LAV group (mean calculated amplitude: 73.8 mmHg reflecting shunt oscillation of 11.2% in mean). In the OAI group oxygen oscillations occurred hours after induction of lung injury (mean calculated amplitude: 57.1 mmHg reflecting shunt oscillations of 8.4% in mean). The SHAM group had no relevant oxygen oscillations (<30 mmHg, shunt oscillations < 1.5%). Synchronously to oxygen oscillations, EIT depicted (1) a decrease of ventilation in dorsal areas, (2) an increase in ventral areas, (3) a decrease of especially dependent expiratory impedance, 3) an increase in late inspiratory flow especially in the dependant areas, (4) an increase in the speed of peak expiratory flow (PEF), and (5) a decrease of dorsal late expiratory flow.
  
  
  CONCLUSIONS
  SpO2 and EIT recordings detect events that are interpreted as cyclical recruitment of atelectasis.
authors.affiliation: 1Department of Anaesthesiology, University Medical Center Mainz, Mainz, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Bodenstein
authors.forename: Stefan
authors.initials: S
authors.lastname: Boehme
authors.forename: Hemei
authors.initials: H
authors.lastname: Wang
authors.forename: Bastian
authors.initials: B
authors.lastname: Duenges
authors.forename: Klaus
authors.initials: K
authors.lastname: Markstaller
mesh_terms: D000818:Animals; D018893:Bronchoalveolar Lavage / Q000009:adverse effects; D017097:Electric Impedance; D019301:Oleic Acid; D010100:Oxygen / Q000097:blood; D001261:Pulmonary Atelectasis / Q000097:blood / Q000209:etiology*; D011897:Random Allocation; D012121:Respiration, Artificial / Q000009:adverse effects*; D013552:Swine; D014054:Tomography; D055397:Ventilator-Induced Lung Injury / Q000209:etiology*
chemical_list: D019301:Oleic Acid; D010100:Oxygen
keywords: acute respiratory distress syndrome; animal experiment; lung injury model; non-invasive monitoring; ventilator-induced lung injury