Ketamine Associated With Morphine PCA After Total Hip Arthroplasty

Ketamine (an analgesic drug often associated with morphine in the treatment of Opioid Induced Hyperalgesia) is often mixed in Morphine PCA syringe. We make the hypothesis that ketamine administrated separately via a continuous infusion, could induced a better analgesic effect. We will perform a randomised double blind study to determine the best infusion mode of intravenous ketamine, associated with morphine in PCA syringe or alone in continuous infusion.