When traveling with a medical bag containing a Continuous Positive Airway Pressure (CPAP) machine or other essential medical equipment, you can typically carry it as hand luggage. In most cases, there is no need to notify the airline in advance.
However, it's always a good idea to check the specific policies of the airline you are traveling with. Ensure that your medical bag meets the carry-on size and weight restrictions. For any specific concerns or questions, it is best to contact your airline directly.