Comparing the changes of arterial anastomotic blood flow between general anesthesia alone and general anesthesia with epidural anesthesia in patients who undergoing free flap transposition using Duplex ultrasound.

Maintaining adequate blood flow is important on the success of free flap surgery. Epidural anesthesia can influence blood flow during surgery. Therefore, investigators aim to compare the effect of epidural anesthesia combined with general anesthesia and general anesthesia alone on blood flow in arterial anastomosis site of the free flap.

Inclusion Criteria:

• Patients scheduled to undergo free flap transfer under general anesthesia.
• 18 years of age or older, under 80 years of age
• Those who voluntarily agreed to participate in this clinical study

Exclusion Criteria:

• If the patient does not agree to participate in the study
• ASA physical status IV or higher
• If the patient was diagnosed with diabetes
• If the patient was diagnosed with chronic renal failure
• If the patient was diagnosed with peripheral vascular disease or hyperlipidemia
• If vasopressors or inotropics was used preoperatively.
• Contraindication of epidural anesthesia such as usage of anticoagulant or abnormalities of laboratory finding.
• If the researcher finds it to be inappropriate