Hello,
The Rebreathers in Scientific Diving Workshop Proceedings (a workshop hosted by the AAUS, DAN, NOAA, and the US National Parks Service at Catalina Is in Feb 2015) were released today.
You can download it here:
https://dl.dropboxusercontent.com/u/...ngs%202016.pdf
In this volume (which contains lots of interesting papers) there is (on page 66) a paper proposing the first published evidence-based guidelines for planning gas density in rebreather dives (or any dives for that matter) in order to avoid dangerous CO2 retention. The paper contains simple examples of how to calculate gas density for any gas mix at any depth.
I hope you find it interesting. I (and I am sure Claudia also) would be happy to answer any related questions.
Simon M