 To investigate whether dexmedetomidine reduce liver injury after hepatectomy. During hepatectomy, surgeons always took inflow occlusion to reduce blood loss with Pringle maneuver. A few clinical studies had shown dexmedetomidine could reduce ischaemiareperfusion IR injury caused by the secretion of reactive oxygen species and inflammatory cytokines. Glutathione-S-transferase GST was a sensitive and specific marker for hepatic injury in several studies before. So the investigator decided to use it as the primary endpoint. Besides, in our center, there are some liver resection surgeries that didnt need occlusion. So it can serve the best placebo for determine the the actual effect of dexmedetomidine on the IR injury in further subgroup analysis. 