Are you billing for the physician's charges or the facility's services? Even if you work for a hospital, there are two different kinds of billing.....facility coding/billing and physician coding/billing. Make sure you're clear about the differences.
I'm going to assume you're billing for the physician. You do not concern yourself with DRG when you submit your charges for physician services using E&M. DRG is calculated from diagnosis codes that are extracted from physician documentation, but is used to report the facility stay....not the physician's work.
So for the physicians in the inpatient setting, you bill the appropriate E&M codes for inpatient services (99221-99223, 999231-99233, 99251-99255, 99234-99236, for example) depending on the situation, documentation guidelines and payer guidelines.
If you are billing for the facility (abstracting the DRG for inpatient services done throughout the admission), then you probably won't be able to get much direction from this discussion board, because most of us are physician coders. But I do know that E&M levels of service are not a consideration with regards to facility inpatient billing/coding.