Inclusion Criteria:  18 years and older, Undergoing outpatient primary total hip arthroplasty under general anesthesia with laryngeal mask, Consent for participation, Affiliation to a social security system  Exclusion Criteria:  Heart rate < 60 bpm Chronic pain syndrome requiring preoperative morphine use (class 3) Contraindication for: paracetamol, ketoprofen, nefopam, oxycodone, propofol, ketamine, cisatracurium, sufentanyl, ropivacaine. Contraindication for dexmedetomidine: hypersensitivity to the active substance or to any of the excipients, advanced cardiac block (grade 2 or 3) unless paced ; uncontrolled hypotension ; acute cerebrovascular conditions Contraindication to laryngeal mask : old insulin-dependent diabetes, gastro-oesophageal reflux, morbid obesity (defined by BMI > 35) Pregnant or breastfeeding women Women of child bearing potential without contraception (any contraceptive method used regularly and appropriately with a low failure rate: <1% per year), A mental or linguistic inability to understand the study, Patient under protection of the adults (guardianship, curators or safeguard of justice), Patient included or planning to be included in another clinical trial relating to medications