This prospective double blinded randomized control trial will include elderly patients over 60 years undergoing orthopedic lower limb surgery under spinal anesthesia single injection (10 mg of Bupivacaine 0,5% with 5 µg of Sufentanyl). We define 4 groups: (1) Patients from 60 to 75 years receiving 100 µg/min of phenylephrine infusion; (2) patients from 60 to 75 years receiving saline infusion; (3) patients over 75 years receiving 100 µg/min of phenylephrine infusion; (4) patients over 75 years receiving saline infusion. Standard monitoring is applied including noninvasive arterial blood pressure, electrocardiography and pulse oximetry. The vasopressor solution and the saline solution will be prepared in identical 50 mL syringes by an investigator not involved in patient care. The investigator administering the solution and the patient are blinded to the content of the syringe. The velocity of infusion will be the same between groups (1ml/min) and the infusion will start once the spinal anesthesia realized. Arterial blood pressure measurements are realized each 1 minute for the first 20 minutes and then each 5 minutes until the end of surgery. After each measurement of MAP, the infusion is stopped if the MAP is more than baseline, and it is continued or restarted if the MAP is less than or equal to baseline. Anyway the infusion is stopped at the end of motor block. Hypotension is defined as a 20% decrease of mean arterial pressure (MAP). Severe hypotension is defined as a 30% decrease of MAP. Hypertension is defined as MAP > 120% of baseline. Each time there is a MAP measurement showing hypotension while patients are under infusion, a 1 mL IV bolus of phenylephrine 100µg/ml is injected by the anesthesiologist involved in patient care. The total volume of study solution given by infusion and the total volume of phenylephrine given by bolus are recorded.