If you are travelling with electronic medical equipment, such as a ventilator, contact the airline as early as possible to discuss your needs. The airline may require further information i.e. serial number etc. and the type of battery. The ventilator should go on as hand luggage.
If you are traveling on a long haul, you may want to consider taking two ventilators, in case there is a problem with one of them. The spare ventilator can be placed under the seat in front of you.
Whatever process is involved it is important that you are in contact with your airline in plenty of time before you fly.