In this study, 20 patients will be randomly assigned to one of two groups: ten patients will have a Serratus anterior plane block (SPB), with a first ropivacaine 0,375% bolus (0,4ml/kg), followed by an infusion of ropivacaine 0,2% at a 10ml/hr rate, through a multi-holed catheter located under the serratus anterior muscle, for a duration of 24 hours. The other group will have a standard intravenous analgesia with a PCA morphine-dehydrobenzperidol pump. Anesthesia protocol will be standardized. Except the infusion of ropivacaine for the SPB, per operative anesthesia and post operative analgesia will be the same for every usual patients.
The investigators will evaluate post operative pain based on the visual analog scale, 24 hours morphine consumption, sensitivity of concerned territory. The investigators will also evaluate post operative chronic pain by assessing pain two months post operatively, completing two questionnaires of neuropathic pain: DN4 and QDSA short form.
Finally, ropivacaine blood concentrations will be dosed by multiple blood samples taken over 24 hours after realizing the SPB, in order to make a population pharmacokinetic analysis, and evaluate the degree of ropivacaine resorption at this level.
