Type of the study: Observational. Subjects: Adult patients ASA 2-3 undergoing elective total knee replacement surgery under general or regional anaesthesia. Sample size calculation (based on expected difference in PRB, alpha error I = 0,05 and study power = 0,99) = 52 patients. Investigators plan to enroll of 60 consecutive patients to reach 30 patients with each type of anaesthesia. Intervention: none. Data to be recorded and analysed: Demographics, ASA, physiologic functions (during surgery and 24 hours after surgery), fluids given, sublingual microcirculation by SDF imaging will be recorded at time points: before anaesthesia, 24 hours after anaesthesia, clinical outcome indicators, microcirculatory data and Perfused Boundary Region.