Effects of intra-abdominal pressure on respiratory mechanics in healthy and injured lungs

Background and goal of the study: Intra-abdominal pressure (IAP) is considered to be a contributing factor to other clinical obesity in the deterioration of respiratory functions. In ARDS, it appears related to abnormalities in lung mechanics [1]. The aim of the study was to evaluate in an adult pig model the effect of IAP on respiratory mechanics, both in healthy and oleic-acid injured lungs. 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. Pressure-volume curves were obtained with supersyringe technique at each experimental step, for total and partitioned (lung and chest wall) static compliance. Multiple comparison was performed with paired t-test, using Bonferroni correction. P < 0.05 was considered to be significant. Results: Total (Elrs), chest wall (Elw) and lung (Ell) elastances (cmH2O L-1) at three different volumes inflated (100, 300 and 700 mL) are reported as mean ± SE. Conclusion: (1) IAP resulted in impaired lung mechanics, both in healthy and in oleic acid injured lungs, independent of volume inflated; and (2) although IAP and oleic acid affect the respiratory system in a different ways, they resulted in the same effects on lung mechanics in some cases.