Question 1195882
In a volume of 250 ml, with 5 micrograms per ml of fentanyl is 1250 micrograms per 250 ml. Each 5 ml amp of fentanyl has a total of 250 micrograms, so you need five of them in the bag, which is 25 ml of fluid altogether. 

I don't know what the volume of the buvivacaine is in each vial. I do know that a total of 0.15625 ml needs to e present for a 250 ml bag to have 0.0625% of the drug.