The primary objective of the study is to characterize and measure the impact of major surgery on the kinetics of endothelial function during the perioperative period. Reactive hyperemia, characterized by Digital Thermal Monitoring (DTM), will be utilized to characterize this during the perioperative period in patients undergoing major abdominal or thoracic surgery. This will attempt to characterize the relationship between impaired endothelial function, the extent of surgical insult, and the risk for adverse postoperative outcome.