If you are an independent fee-for-service contractor it's a breeze. My overhead used to be 5%. Fill out a thirty second ticket for each case, enclose a face sheet (patient's info, insurance, etc) and a copy of the anesthesia record. Time start, time end, name of patient, diagnosis, procedure (in simple terms is sufficient), total units (simple to compute). Stuff it all in an envelope for the day and off to your billing agency who takes their 5% and sends you a report every week on the collections. Pretty easy. Real easy.