Clinical and Multi-omics Study on Gut Microbiota in Critical Ill Patients After Cardiovascular Surgery Combined Cardiopulmonary Bypass With or Without Sepsis（CPB-MUL-GM Study): a Prospective Study Protocol

This protocol is designed as a prospective observational case-control study in patients who underwent cardiopulmonary bypass (CPB) due to cardiac surgery. 30 healthy persons were selected as control group. The case group included patients admitted to intensive care unit (ICU) after cardiac surgery and extracorporeal circulation which is performed by the Department of cardiac surgery of Peking Union Medical College Hospital. The patients enrolled should be divided into two groups according to their primary outcomes: one grouped fever and/or hemodynamic instability after cardiopulmonary bypass and the other grouped normothermia and normal hemodynamic during 48 hours after surgery(cause an infection manifested >48 hours after admission was defined as hospital acquired. ). Sample collection was terminated when both groups received 30 cases. These 60 cases would regard as the case group. Additionally, all the CPB patients we observed will be divided into survivors and non-survivors based on the 28-day survival. Feces and blood samples will be obtained at certain time points（initial sampling at least one day before the surgery, repeat sampling within 24-48 hours after CPB）. The fecal samples analysis will apply metagenomics and the feces and blood samples will be analyzed using untargeted metabolomics method. In this study, the stratification of gut microbial communities in patients underwent extracorporeal circulation were explored and analysed the variation of metabolite in patients's plasma and fecal samples. Predictive bio-markers and possible pathogenesis of fever and/or hemodynamic instability after CPB will be also provided by clinical outcomes analysis combined with multi-omics study.