Continuous bupivacaine administration through an elastomeric pump (Pain Buster) has been found effective for post operative analgesia in a large range of surgery. Ropivacaine is a less toxic drug, never tested in the surgery of latissimus dorsi and serratus micro anastomotic flaps (from the investigators knowledge). The aim of the study is to evaluate the usefulness of this drug and device for post operative analgesia, associated with patient controlled analgesia with morphine. For this purpose a controlled randomized double blind trial against placebo (saline) is performed, enrolling 40 (20x2) patients during 3 years, in order to measure total morphine consumption during the first 48 post operative hours and to evaluate analgesia and sides effects of morphine in each group.