title: Use of dynamic CT in acute respiratory distress syndrome (ARDS) with comparison of positive and negative pressure ventilation.
abstract: Negative pressure ventilation via an external device ('iron lung') has the potential to provide better oxygenation with reduced barotrauma in patients with ARDS. This study was designed to see if oxygenation differences between positive and negative ventilation could be explained by CT. Six anaesthetized rabbits had ARDS induced by repeated saline lavage. Rabbits were ventilated with positive pressure ventilation (PPV) and negative pressure ventilation (NPV) in turn. Dynamic CT images were acquired over the respiratory cycle. A computer-aided method was used to segment the lung and calculate the range of CT densities within each slice. Volumes of ventilated lung and atelectatic lung were measured over the respiratory cycle. NPV was associated with an increased percentage of ventilated lung and decreased percentage of atelectatic lung. The most significant differences in ventilation and atelectasis were seen at mid-inspiration and mid-expiration (ventilated lung NPV = 61%, ventilated lung PPV = 47%, p < 0.001; atelectatic lung NPV = 10%, atelectatic lung PPV 19%, p < 0.001). Aeration differences were not significant at end-inspiration. Dynamic CT can show differences in lung aeration between positive and negative ventilation in ARDS. These differences would not be appreciated if only static breath-hold CT was used.
authors.affiliation: Department of Diagnostic Imaging, The Hospital for Sick Children, Toronto, Canada. emmajhelm@hotmail.com
authors.forename: Emma
authors.initials: E
authors.lastname: Helm
authors.forename: Omid
authors.initials: O
authors.lastname: Talakoub
authors.forename: Francesco
authors.initials: F
authors.lastname: Grasso
authors.forename: Doreen
authors.initials: D
authors.lastname: Engelberts
authors.forename: Javad
authors.initials: J
authors.lastname: Alirezaie
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kavanagh
authors.forename: Paul
authors.initials: P
authors.lastname: Babyn
mesh_terms: D000818:Animals; D008168:Lung / Q000000981:diagnostic imaging*; D008297:Male; D018467:Positive-Pressure Respiration, Intrinsic; D011817:Rabbits; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome; D015919:Ventilators, Negative-Pressure