Caspofungin is an anti-fungal drug mainly metabolized by the liver. The pathophysiological status of children with severe infection will affect the metabolism of caspofungin in the body especially in the case of liver dysfunction. There is little metabolism of caspofungin through the kidney and continuous renal replacement therapy and renal function have little influence on the pharmacokinetics of caspofungin. The study aim to investigate PK/PD of caspofungin in children with specific pathophysiological conditions, such as liver insufficiency, hypoproteinemia, ECMO treatment, or sepsis.