Effect of different mechanical ventilation techniques on the pulmonary oxidative stress induced by a model of acute respiratory distress syndrome in rabbits

Abstract

Background: The acute respiratory distress syndrome (ARDS) is characterized by an inflammatory process that causes a disruption of the alveolar-capillary barrier with consequent interstitial and alveolar edema, decrease in lung compliance, pulmonary hypertension, ventilation/perfusion mismatch, and refractory hypoxemia. Despite its pathophysiology being better understood and recent advances in treatment, mortality rate is still high, varying from 40% to 60%. Although the exact ARDS mechanism is unknown, various evidence suggests that patients with the syndrome are exposed to a high level of oxidative stress (OS) induced by a variety of events. The OS is caused by an unbalance between defense antioxidant system and generation of reactive oxygen species (ROS) or nitrogen (RNS), which leads to the accumulation of oxidative lesion on the biomolecules. Although the administration of antioxidants has shown some benefits on the ARDS evolution, there is no clinical evidence for its use. However, pulmonary mechanical ventilation (MV) constitutes one of the main treatments in ARDS, capable of changing the evolution of the disease and reduce mortality. There are two ventilatory methods for lung protection which are used in ARDS. One is based on conventional MV (CMV) and the other on high-frequency oscillatory ventilation (HFOV). Objective: To investigate oxidative pulmonary stress through total antioxidant performance (TAP) in saline-lavaged rabbit model of ARDS ventilated on conventional protective mechanical and HFOV. Methods: The study was approved by Institution's Animal Care and Use Committee and will be developed at Pediatrics Department's Clinical Research Laboratory-Botucatu Medical School - UNESP (protocol n° 600). Animal preparation and randomization: this is a prospective, controlled, in vivo study on the laboratory animals. The animals will be young white rabbits supplied by UNESP's bioterio with body weight varying from 2,0Kg to 3,0 Kg. Experimental groups: the animals will be selected at random to form three experimental groups, each with 10 animals:- healthy animals submitted to MV (control)- ARDS animals submitted to protective MV ( GMV)- ARDS animals submitted to HFOV ( GHFOV)Determination of the lung oxidative injury: the OS will be evaluated through the TAP method described by Aldini et al. (2001). This method is based on lipophilic similar oxidation (probe) known as BODIPY [4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid] and through a lipoperoxil radical generator (LOO*) with a lipophilic compartment denominated MeO-AMVN [2,2¢-azobis(4-methoxy-2,4-dimethylvaleronitrile)]. The BODIPY oxidation originates fluorescence green product which can be detected on a fluorescence light emission counter. The acid (BODIPY 581/591) will be supplied from molecular probes (Eugene, OR, USA) and Meo-AMVN, from Wako Chemicals (Richmond, VA, USA).Statistics analysis: variables with normal distribution will be compared within the groups and assessed by variance analysis (ANOVA), with subsequent multiple comparison among pairs through Studen-Newman-Kewls test. Non-normal distribution variables will be compared among the groups through Kruskal-Wallis ANOVA, with subsequent comparison with the Dunn test. The analysis of a variable during the time of the test will be assessed through Friedman repeated measures, with posterior comparison with Dunnett's method. Differences were considered significant at p < 0.05. (AU)