This study focuses on a method of decreasing and maintaining blood pressure at a deep hypotensive state by automatically infusing sodium nitroprusside, and presents how to increase blood pressure back to higher value through controlling noradrenaline infusion. To handle the behaviors of patient caused by multiple feedbacks of blood pressure autoregulatory mechanisms and a wide range of patient sensitivities, a physiological model was developed. It can be used not only for tuning the controller but also for simulating the reaction of the body. The control system can simulate the circulation during and after administered hypotensive or hypertensive agents. At starting time, a step infusion is applied to estimate patient sensitivities. These parameters were used for configuring a fuzzy gain scheduler of a PID controller with an online supervising algorithm for updating the scheduler which can make the PID controller acting stronger or weaker due to the behaviors of patients. The control system was tested on pigs. The experimental results showed a stability and safety of the control system that indicated a possibility of the proposed method.