Hi Fernando
Transaction MD04 shows all the relevant POs for a material. In some specific cases, the PO is displayed, but it does not affect the available quantity (see note 1825187).
If you want to have a more detailed control, you can create an implementation of BAdI MD_CHANGE_MRP_DATA. See the following link for more details about the BAdIs available on MRP:
http://scn.sap.com/community/erp/manufacturing-pp/blog/2013/08/12/badis-for-mrp
BR
Caetano