Induced hypovolemia is known to improve surgical field during living donor hepatectomy. This procedure is conventionally guided by monitoring the central venous pressure (CVP). Stroke volume variation (SVV) is a novel method to substitute with CVP to monitor cardiac preload. The investigators try to evaluate the relationship between CVP and SVV during CVP-guided vasodilator induced hypovolemia (validation study). Then, feasibility of vasodilator induced hypovolemia using the SVV calculated from the validation study will be tested (feasibility study).