Evaluation of tissue blood flow for the digestive tract and the liver by finger-mounted tissue oximetry during peri-oerative period in patients undergoing gastroenterological and hepatobiliary surgery

Interventions: finger-mounted tissue oximetry
Primary outcome(s): The average values of tissue blood flow (tissue oxygen saturation: rSO2, and total hemoblobin index: T-HbI) in each gastrointestinal tract and the liver.
Study Design: Single arm Non-randomized