I have a question about how to use fentanyl during surgery. In my clinic, fentanyl is used in CRI when invasive procedures are expected or when the MAC sparing effect is expected in sick animals. I feel that the dose of fentanyl that we use (1-5 ug/kg/hr) did not produce the MAC sparing effect of isoflurane. I don't know if this is because the pain relief is inadequate, or another analgesia is needed. It seems that the MAC sparing effect of medetomidine as a premedication is larger than fentanyl. Should I use a loading dose of 5ug fentanyl before the CRI?