I'll echo what others have said, which is that just because the patient was on a Fentanyl patch does not preclude IV fentanyl, even for a renal patient.
The Fentanyl patch is most likely for chronic pain, and is most likely enough to control the patient's chronic pain. But this patient had surgery, which is acute pain, and most likely unaffected by the Fentanyl patch. IV Fentanyl for acute/breakthrough pain is not unreasonable for this patient.
Without knowing what the order was and how much was given, I can't comment on how this happened. It's impossible to predict each individual person's response to any medication, and if the order was within reasonable limits for the individual patient's circumstances, then I don't see how either the physician or the nurse would be to blame.
It's possible that a med error was made, and the patient given too large a dose, like my friend who was overdosed while in the hospital. The order was for 1mg of Dilaudid, and the nurse gave my friend 10mg of Dilaudid. Needless to say, they had to call a rapid response.
We just don't know enough details to give a reaonable explanation of what happened. The fact that his blood sugar was 64 after juice tells me it was probably somewhere around 50 initially, and coupled with the fact that he responded to the D50, this tells me that there was more going on than just the Fentanyl.
What's more concerning to me is your anger about it, and it seems you are blaming the doctor. I like to reserve anger for those who are knowingly careless or sloppy and who knowingly disregard the safety and well-being of the patient. We don't know that the doctor in this situation did any of those things. We don't have all the facts, and you probably don't either.
Hopefully your facility uses an incident reporting system in which all the facts are gathered, synthesized, and analyzed, to find out where the process needs to be improved in order to prevent the same thing from happening in the future, and this incident will be used to make improvements in processes to help enhance patient safety.