This study is a randomized controlled trial. It will randomize 160 patients who are scheduled for Robot-Assisted Radical Prostatectomy. The intervention group will receive a single spinal injection of a bupivacaine (12,5 mg)/morphine(300 mcg) mixture. Controlgroup will receive a subcutaneous injection of lidocaïne for placebo purposes and an intravenous loading dose of morphine at the end of surgery.