For RSI, all drugs are based on total (actual) body weight rather than ideal body weight, except ketamine, for which you are supposed to use ideal body weight. You can remember this by keeping in mind that ketamine is the ideal RSI agent. So ideal, that if you give it based on TBW rather than IBW as recommended, it doesn’t matter. Propofol is a little funky, they recommend IBW+TBW(.4). Morphine is dosed based on IBW, whereas you’re supposed to use TBW for fentanyl. I doubt that these recommendations are based on much science, but when you have to pick a dose, it’s something.
From Brunette, AmJEM, 2004. doi:10.1016/S0735-6757(02)42250-4
Thanks to Erin Robey for finding this for me.
Opiate Opioid Conversion Chart: