The lavage will be performed immediately prior to closure of the wound, once placed the drainage into the cavity. In both groups, prior to the lavage, a microbiological sample from the surgical bed will be obtained with a swab (sample 1), followed by a lavage with 500 ml normal saline. After aspiration of the saline, a new microbiological sample will be obtained (sample 2). In Group 1 a second lavage with 500 ml normal saline will be performed, while in Group 2 the second lavage will be performed with an antibiotic solution, including gentamicin (240 mg) dissolved in 500 ml normal saline. After aspirating this second lavage, a third microbiological sample will be obtained in the same way as the two previous ones, in both groups (sample 3).