Objective: To describe the perioperative biomarker response in surgical patients with and without a postoperative complication and construct a preoperative and postoperative prediction model for postoperative complications. To systematically collect perioperative blood samples and clinical data in high-risk surgical patients for the development en analysis of biomarkers. Study design: Multicenter, prospective, observational study. Study population: 4819 patients undergoing elective cardiac, colorectal, vascular and lung surgery. Intervention (if applicable): Not applicable. Main study parameters/endpoints: Main study parameters are levels of PCT, CRPhs, IL-6, GDF-15, sFLT, NT-proBNP, cTNThs, CysC and NGAL. Main study endpoint is the occurrence of a major postoperative complication which is defined as a surgical site infection, pneumonia, sepsis, acute kidney injury, major adverse cardiovascular events or death within 30 days of surgery. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: In each patient five blood samples will be drawn for analysis. Most of the blood samples are drawn simultaneously with routine perioperative laboratory testing, which is common in this study population. In case a patient is admitted to the Intensive Care Unit blood samples will be collected using an arterial line. There are no direct risks or benefits for patients included in the study.