 Previous studies on animals suggest that inhalational anesthetics can reduce vascular tension in vitro resulting in vasodilation and decrease in blood pressure. This role for inhalational anesthetics has essential clinical implications such as the condition of sepsis or septic shock or other shock-associated states during which the blood vessel constricts strongly and leads to circulation dysfunction. The vasodilation property of these anesthetics including halothane, isoflurane, sevoflurane, desflurane and enflurane enables them to be better options than other general anesthetics in many clinical conditions needing the vasculature to be dilated. The investigators hypothesized that these inhalational anesthetics can evoke vasodilation measured with ultrasonography during general anesthesia in vivo as the in vitro studies displayed. 