This reminds me of the scene in The Abyss where the rat is forced to breathe in oxygen-rich perfluorocarbons[1]. I think this idea of introducing oxygen through perfluorocarbons has been explored but not sure it’s made much headway in humans to date [2]. This paper seems like a clever idea to introduce the liquid anally where oxygen can diffuse through the linings,
and to also use same liquid (because of its viscosity) to scrub the intestines of mucus, to facilitate the oxygen diffusion process.
[1] https://filmschoolrejects.com/the-abyss-breathing-fluid/?amp
[2] https://en.m.wikipedia.org/wiki/Liquid_breathing