Oleic acid and intra-abdominal pressure effects on lung morphology in an experimental animal model

Background and goal of the study: Alveolar collapse is well established to be one of the most important pulmonary alterations during ALI/ARDS. Moreover, increased intra-abdominal pressure (IAP) is a cofactor of the deteriorating respiratory function in ALI/ARDS [1]. The aim of this study was to assess by CT scan the effects of increased IAP on lung morphology, both in healthy animals and an oleic acid-induced ARDS model. Materials and methods: Seven anaesthetized and paralysed domestic pigs were ventilated at 12 mL kg-1 VT, 5 cmH2O PEEP, 12-14 b min-1 RR, 1.0 FiO2. The animals were subjected to a four-step protocol: (1) healthy lungs with IAP = 0 and (2) 20 cmH2O, (3) oleic acid-injured lungs with IAP = 0 (OA IAP 0), and (4) 20 cmH2O (OA IAP 20). IAP was performed by an air pneumoperitoneum, lung injury by intravenous administration of 0.15 mL kg-1 OA. Pulmonary CT scans were performed within a 14-17 s end-expiratory hold manoeuvre. For each end-expiratory CT scan, the percentage of normally (A), poorly (P) and non-aerated (N) tissue was computed as the frequency of voxels, respectively, with a CT number between -1000/-501 HU, -500/-101 HU and -100/+200 HU [2]. Multiple comparison was performed with paired t-test, using Bonferroni correction. P < 0.05 was considered to be significant. Results: Results are reported in the table as mean ± SE, expressed as a percentage of the total lung volume. Conclusion: (1) IAP resulted in impaired lung aeration both in healthy and in oleic acid injured lungs; (2) IAP and oleic acid seem to affect lung parenchyma with identical effects.