BAPI for PURCHASE ORDER with OPEN QUANTITY field

Hi All,

I wanted to use the BAPI_PO_GETDETAIL to get the Purchase Order details upon triggering from Warehouse management system,

But the details required contains a field called OPEN QUANTITY...which is not used in this BAPI.

I request to let me know if any BAPI exits for PO details having the structure for this field:Open Quantity.

Am using SAP version 4.0B.

If not exists please advise how to customize the existing BAPI to meet the requirement.

thanks

mahi