You must read your manual first. However, generally, most modern cpaps will adjust voltage automatically. All you need is the proper plug in adaptor for the country you will be visiting . You can purchase a kit with all of the plug adaptors from Wal Mart for about $10.00. Look in the luggage section.
I have traveled all over the world with my Resmed spirit. No problems.
ALWAYS carry your CPAP onto the plane with you . It is a medical device and does not count as carry on ..The airline may not seperate you from your CPAP. Besides, its tough but still fragile, especially the mask. I got rid of the soft case that came with it and put it in one of those soft side coolers with the plastic insert. Gives it a bit more protection and a few more compartments to store your ticket , passport etc.
One problem that I have encontered. Many hotels hardwire the lamps so that there are no outlets near the bed. I carry along a 15 ft. extension cord to reach an outlet . This has happened at Marriott County Hall in London. I had to move the bed (king ) to reach the outlet on the desk. This has ocured twice .
Good Luck,
Chris