<qa>  What is the plasma sample used for?6. We will establish a sub-group that contains 20 patients chosen from enrolled patients according to APACHE II scores: 10 patients are APACHE II scores in 21-30. We will take one blood sample daily during the whole study period. The plasma sample will be used for metabolomics analysis using an 800 MHz 1H-NMR-UPLC-MS system. And the data will be used for metabolic dynamic modeling. 