The effects of different pressure on lung histopathology in rat abdominal compartment syndrome model

Background and Aim: Abdominal compartment syndrome (ACS) is disease with high mortalitly if not diagnosed and treated early. Restrictive pulmonary abnormalities are prominent in this disorder. Patients with primary ACS will often develop a secondary acute respiratory distress syndrome (ARDS) and will require specific treatment. Mechanic pressure is mainly responsibe in pulmonary findings in ACS. In the present study we aimed the role of aspiration of gastric contents into lower airways in pulmonary complications of ACS.Methods: This study is designed as a single-blind controlled experimental trial. Fifty female, isolated from male, Wistar-Hannover rats that weighed 200-220 grams were used in the study. The 50 rats were initially divided into five groups of 10 animals in each group (Group I-V), and then these groups were divided again into two groups of 5 animals in each group if they are unfed (Group Ia-Va) or fed (Group Ib-Vb). The abdomen was shaved and under aseptic conditions in all anesthetized rats, a 1 cm midline laparotomy with vertical incission was performed. An intraperitoneal catheter was placed and exteriorized at the lower end of the incision. The midline laparotomy was closed with a running suture so the way the intraperitoneally placed catheter was encircled and provide a water proof closure of the abdominal cavity. In animals in group Ia-Va intraperitoneal pressure (IAP) was applied as follows: 15cm H2O in group Ia, 20cm H2O in group IIa, 25cm H2O in group IIIa and 30 cm H2O in group IVa by instillation of isotonic saline solution. The animals in group Ib-Vb were fed by 2 cc methylene blue with the help of gavage directly to stomach 30 sec before the same pressure was applied. The IAP was kept constant for 1h after the target pressure was reached. In control group ( Group V) no intraabdominal pressure was applied to the animals, but half of them was fed by methylene blue in same way. All anesthetized rats were sacrificed by removal of their lungs for histological examination. Experiments were performed in accordance with the Afyon Kocatepe University Etic Committee legislation for the care and use of laboratory animals.Results: Total scores of lung histopathologic findings were concordant with the degree of IAB. When the total scores of histopathologic findings in lungs were compared for each applied IAB with control group , the scores were higher in fed animals than unfed animals. Histopathologic findings in lungs were observed when increased-IAP to 15 mmHg (20 cm H2O) which was accepted as cut-off value. The comparison of the scores of histopathologic findings in two groups in which the applied IAB was lower then the cut-off value were not significantly different from the control group. However comparison of the scores of histopathologic findings equal to or above 18 mmHg were significantly higher then the control group.Conclusion: Pulmonary changes in IAP is prominent when IAP is incresed more than of 15 mmHg (20 cm H2O). The scores of histopathologic findings were significantly higher in fed animals. The histopathologic findings in the lungs seen in our rats in which increaed-IAP was equal to or more than 18mmHg were suggestive for pulmonary aspiration. Our results show that that pulmonary aspiration related with passive regurgitation in ACS has a substantial influence on histopathologic findings seen in this disorder. In clinical trail the physician must be alert for close monitorization and early decompression when IAP is equal to or more then 15 mm Hg.