Many cats like to chew on plastic things. Becky P. writes to us about her cat, Keepers:
Becky, our black spokescat, Mina, loves to chew on plastic things too. The more flexible the plastic, the more she likes it. We're not sure why some cats love to chew on plastic things when others ignore it, but it can become a problem when that fixation turns to something inappropriate like power cords or your oxygen tubing.
There are some plastic sleeves that are sold for the express purpose of protecting cords and cables from chewers, but in our opinion, these actually encourage the behavior. You want Keepers to associate something bad with the behavior, but not with you or with his home in general.
In your particular case, the easiest way to deal with it will be to coat your tubing with something that tastes awful to Keepers. There are sprays that are designed for this, but we dislike them because they contain some iffy ingredients. We'd recommend you use a simple bottle of lemon juice. Cats generally despise citrus of any sort and lemon juice is readily available. Douse a cotton ball in the juice and simply rub it on the tubing. Once it dries, you shouldn't even smell it, but Keepers with get a good taste of horrible (to him) citrus with every bite. He'll soon associate the tubing with the bad taste and should stop chewing it. You may need to refresh the juice from time to time but once Keepers associates the bad taste with the tubing, he should give it a wide berth.
In addition, it will help to give Keepers some plastic toys that he can chew on. Something that doesn't resemble your tubing, of course. For our plastic-lover, we've been able to satisfy this need with Looney Loops. You can see our review of this toy here.
Becky, we're confident that you'll be able to get Keepers to keep away from your oxygen tubing. It'll just take a little time. Even if it doesn't seem to work at first, keep at it. Consistency is the number one rule when it comes to training!