title: The impact of spontaneous ventilation on distribution of lung aeration in patients with acute respiratory distress syndrome: airway pressure release ventilation versus pressure support ventilation.
abstract: BACKGROUND
  In this study, we sought to determine which mode, airway pressure release ventilation (APRV) or pressure support ventilation (PSV), decreases atelectasis more in patients with acute lung injury/acute respiratory distress syndrome (ARDS).
  
  
  METHODS
  This was a retrospective study in the intensive care unit. Between 2006 and 2007, we identified 18 patients with acute lung injury/ARDS who received either APRV or PSV and had a helical computed tomography scan twice in 3 days.
  
  
  RESULTS
  Computed tomography data from the APRV and PSV groups (n = 9 each) were analyzed for 3-dimensional reconstruction and volumetry. Aerated lung regions (normally aerated, poorly aerated, nonaerated, and hyperinflated) were identified by their densities in Hounsfield units. The Pao(2)/Fio(2) ratio and alveolar-arteriolar oxygen gradient after ventilation were improved in both groups (P = 0.008); however, the improvements in the APRV group exceeded those in the PSV group when delivered with equal mean airway pressure (P = 0.018 and 0.015, respectively). Atelectasis decreased significantly from 41% (range, 17%-68%) to 19% (range, 6%-40%) (P = 0.008) and normally aerated volume increased significantly from 29% (range, 13%-41%) to 43% (range, 25%-56%) (P = 0.008) in the APRV group, whereas lung volume did not change in the PSV group.
  
  
  CONCLUSIONS
  Spontaneous ventilation during APRV improves lung aeration by decreasing atelectasis. PSV for gas exchange is effective but not sufficient to improve lung aeration. These results indicate that APRV is more efficient than PSV as a mode of primary ventilatory support to decrease atelectasis in patients with ARDS.
authors.affiliation: Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871, Japan. doctor@mvj.biglobe.ne.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Rinka
authors.forename: Arito
authors.initials: A
authors.lastname: Kaji
authors.forename: Akira
authors.initials: A
authors.lastname: Yoshimoto
authors.forename: Hideki
authors.initials: H
authors.lastname: Arimoto
authors.forename: Toshinori
authors.initials: T
authors.lastname: Miyaichi
authors.forename: Masanori
authors.initials: M
authors.lastname: Kan
mesh_terms: D055371:Acute Lung Injury / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D045422:Continuous Positive Airway Pressure; D005260:Female; D006439:Hemodynamics; D006801:Humans; D021621:Imaging, Three-Dimensional; D007362:Intensive Care Units; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D011857:Radiographic Image Interpretation, Computer-Assisted; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*; D012189:Retrospective Studies; D013997:Time Factors; D036542:Tomography, Spiral Computed; D016896:Treatment Outcome