It really depends on what is documented. Typically if a procedure is planned in advance and that's the only thing done, then an E&M charge is not warranted. But if the patient is being evaluated for a problem, and during the course of the evaluation the provider determines that the procedure is a necessary step in the diagnosis of the problem and/or formation of a plan of care, you can probably justify the E&M service and modifier 25.
But are they really doing an exam under general anesthesia in the office (92502)? General anesthesia is usually a facility service and the code is set up in the RVU table with a non-facility 'NA' indicator which means 'rarely or never performed in the non-facility setting.' If you're using 92502, that's why you're seeing such low payment - the code is valued just on the physician work and is not set up to capture any of your facility costs.