Double-blind Study to Assess effectIveness of Pectoral Nerves Block After Breast Surgery on Piritramide Consumption

This is a double-blind study that will randomise breast cancer subjects in 1:1 ratio to receive a "pecs block" of 10 ml of Ropivacaine 3.5 mg/ml and Clonidine 5 µg/ml injected between pectoral muscles and 20 ml between the muscles pectoralis minor and serratus anterior (arm A) versus 10 ml of placebo (NaCl 0.9%) injected between pectoral muscles and 20 ml between the muscles pectoralis minor and serratus anterior (arm B). The pecs block will inject just before the surgery. Subjects will receive a nausea and vomiting prophylaxy depending on Apfel score After surgery, the two intervention groups will receive before waking a dose of Paracetamol (1 g) and Diclofenac (75 mg), if they present no contraindications and a dose of 0.05 mg/kg Piritramide . In the recovery room the two groups will benefit from a Patient Controlled Intravenous Analgesia (PCIA) pump - Piritramide allowing them to control their analgesia, which will be stopped at 24 hours postoperatively.