Intravenous dexmedetomidine is a drug used in reanimation with sedative, anxiolytic and
sympatholytic properties. Recent studies showed useful properties for anaesthesia : decrease
of morphine consumption after a various type of surgery, sedative effect on patients under
regional anaesthesia, prolongation of central or peripheral regional block. Dose-ranging
study for intravenous dexmedetomidine showed that 2 µg/kg is an effective dose to prolong
interscalene block. This study aims to determine if intravenous dexmedetomidine at 2 µg/kg
allows a longer analgesic duration after a quadri-block (femoral, subgluteal sciatic,
obturator and alateral cutaneous nerve blocks) with ropivacaine 0.32% for total knee
replacement under regional anaesthesia.