Are There Any Devices That Can Be Used To Keep

Are there any devices that can be used to keep from sleeping on your av fistula in your arm. My dad has had to have his cleared about 6 times in the last 15 months. He's 78 and feels bad all of the time and having to go in so often to have it cleared is frustrating for him. He's always slept with his arm under is head but has since stopped after getting the fistula. I think he may be doing it after he falls asleep.