title: Influence of inspiration to expiration ratio on cyclic recruitment and derecruitment of atelectasis in a saline lavage model of acute respiratory distress syndrome.
abstract: OBJECTIVE
  Cyclic recruitment and derecruitment of atelectasis can occur during mechanical ventilation, especially in injured lungs. Experimentally, cyclic recruitment and derecruitment can be quantified by respiration-dependent changes in PaO2 (ΔPaO2), reflecting the varying intrapulmonary shunt fraction within the respiratory cycle. This study investigated the effect of inspiration to expiration ratio upon ΔPaO2 and Horowitz index.
  
  
  METHODS
  Prospective randomized study.
  
  
  METHODS
  Laboratory investigation.
  
  
  METHODS
  Piglets, average weight 30 ± 2 kg.
  
  
  METHODS
  At respiratory rate 6 breaths/min, end-inspiratory pressure (Pendinsp) 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and FIO2 1.0, measurements were performed at randomly set inspiration to expiration ratios during baseline healthy and mild surfactant depletion injury. Lung damage was titrated by repetitive surfactant washout to induce maximal cyclic recruitment and derecruitment as measured by multifrequency phase fluorimetry. Regional ventilation distribution was evaluated by electrical impedance tomography. Step changes in airway pressure from 5 to 40 cm H2O and vice versa were performed after lavage to calculate PO2-based recruitment and derecruitment time constants (TAU).
  
  
  RESULTS
  In baseline healthy, cyclic recruitment and derecruitment could not be provoked, whereas in model acute respiratory distress syndrome, the highest ΔPaO2 were routinely detected at an inspiration to expiration ratio of 1:4 (range, 52-277 torr [6.9-36.9 kPa]). Shorter expiration time reduced cyclic recruitment and derecruitment significantly (158 ± 85 torr [21.1 ± 11.3 kPa] [inspiration to expiration ratio, 1:4]; 25 ± 12 torr [3.3 ± 1.6 kPa] [inspiration to expiration ratio, 4:1]; p < 0.0001), whereas the PaO2/FIO2 ratio increased (267 ± 50 [inspiration to expiration ratio, 1:4]; 424 ± 53 [inspiration to expiration ratio, 4:1]; p < 0.0001). Correspondingly, regional ventilation redistributed toward dependent lung regions (p < 0.0001). Recruitment was much faster (TAU: fast 1.6 s [78%]; slow 9.2 s) than derecruitment (TAU: fast 3.1 s [87%]; slow 17.7 s) (p = 0.0078).
  
  
  CONCLUSIONS
  Inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs. Time constants for recruitment and derecruitment, and regional ventilation distribution, reflect these findings and highlight the time dependency of cyclic recruitment and derecruitment.
authors.affiliation: 1Department of Anesthesia, General Intensive Care, and Pain Management, Medical University Vienna, Vienna, Austria. 2Department of Anesthesiology, Medical Center of the Johannes-Gutenberg University Mainz, Mainz, Germany. 3Beijing Institute of Pharmacology and Toxicology, National Beijing Center for Drug Safety Evaluation and Research, Beijing, People's Republic of China. 4Department of Cardiovascular Surgery, German Heart Center Munich, Munich, Germany. 5Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University Vienna, Vienna, Austria. 6Oscillogy LLC, Folsom, PA.
authors.forename: Stefan
authors.initials: S
authors.lastname: Boehme
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Bentley
authors.forename: Erik K
authors.initials: EK
authors.lastname: Hartmann
authors.forename: Shi
authors.initials: S
authors.lastname: Chang
authors.forename: Gabor
authors.initials: G
authors.lastname: Erdoes
authors.forename: Anatol
authors.initials: A
authors.lastname: Prinzing
authors.forename: Michael
authors.initials: M
authors.lastname: Hagmann
authors.forename: James E
authors.initials: JE
authors.lastname: Baumgardner
authors.forename: Roman
authors.initials: R
authors.lastname: Ullrich
authors.forename: Klaus
authors.initials: K
authors.lastname: Markstaller
authors.forename: Matthias
authors.initials: M
authors.lastname: David
mesh_terms: D055371:Acute Lung Injury / Q000503:physiopathology; D000818:Animals; D001784:Blood Gas Analysis; D045853:Exhalation / Q000502:physiology; D001239:Inhalation / Q000502:physiology; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D001261:Pulmonary Atelectasis / Q000503:physiopathology*; D011897:Random Allocation; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D013552:Swine; D007507:Therapeutic Irrigation