Dose conversion between remifentanil and fentanyl
Hello all! UK-based anaesthetist in training here.
So we've all seen conversion tables for dosing equivalence between different opioids. This is never an exact science but for longer acting opioids this is in some ways relatively straightforward in that we're basically asking "What bolus dose of opioid X do I give to get the same peak effect as with a certain bolus dose of opioid Y?"
But this gets more interesting and challenging to compare with remifentanil. As it is ultra-short acting, a bolus only achieves its peak effect maybe a minute or so before it starts to clinically wear off, and so we usually give it as an infusion e.g. in mcg/kg/min, or more commonly in my country, as a target-controlled infusion with a plasma/effect site concentration (CpT/CeT) in ng/ml using the Minto or Eleveld-Remifentanil models (as a very rough approximation for practitioners not familiar with one system or the other, an infusion rate of 0.1 mcg/kg/min at steady state is similar to a CpT/CeT of 3 ng/ml).
Which leads to my question: How do anaesthetists, anaesthesiologists, and CRNAs convert between the peak effect you get with a bolus dose of fentanyl and the effect of a certain infusion rate or CpT/CeT of remifentanil?
I have done a little reading on studies comparing the potencies of these two drugs myself which gives me perhaps some idea, but I'm asking this today as I'm curious about how other practitioners think of this. I'm interested in how people mentally model remifentanil in relation to other opioids or whether they think of it in a different category altogether (which at least one person has told me they do). If you are more of an alfentanil/sufentanil than a fentanyl person, feel free to share instead how you compare these to remifentanil.