Gut hypoperfusion - reperfusion injury is an unavoidable event at the end of laparoscopic surgery. It produces oxidative stress (reactive oxygen species). Malondialdehyde have been demonstrated to be a reliable biomarker for the evaluation of oxidative stress in vivo. Propofol (2, 6 - diisopropylphenol), a highly liposoluble anaesthetic, has a potent antioxidant activity against lipid peroxidation in both in vitron and in vivo studies. On the basis of this knowledge, the investigators hypothesized that propofol has preventive effect for gut hypoperfusion - reperfusion induced injury in robot-assisted laparoscopic radical prostatectomy.