RecruitingClinical trialOxidative Lipidomic Biomarkers During Mechanical Ventilation in Critically Ill Patients (OXY-BAL).The aim of this study is to identify and determine the levels of oxidized lipids and lipid mediators following exposure to oxygen supplementation during mechanical ventilation by oxidative lipidomics. The investigators will include patients with mechanical ventilation and have received FiO2=\>0.5 atleast 90 minutes and collected two sequential mini bronchoalveolar lavage on them 24 hours apart. Mass Spectrometry Lipid chromatography will be conducted and clinical data will be analyzed.