Kidney transplant can help patients with end-stage kidney disease to get rid of dialysis and have a good quality life. However, during the renal donation operation, the stress response and subsequent inflammatory responses may result in damage to the residual kidney and transplanted kidney. Dexmedetomidine can increase urine output and decrease the neutrophil gelatinase associated lipocalin level in patients receiving coronary artery bypass surgery. The primary goal of this trial is to investigate the effects of perioperative infusion of dexmedetomidine on the microcirculation and residual kidney function in kidney donors and on the transplanted kidney function in kidney recipients.