Modern CPAP machines (ex. AirSense 10) can operate all over the world. The universal power supply is rated from 100-240 V, 50-60 Hz and can be used without a voltage converter in most countries. An international plug adaptor may be required to make your power cord compatible with the power outlets of the country to which you are traveling to.
Review your CPAP machine user manual for your machine's technical specs here.