EFFECTS OF REMIFENTANIL, A NEW SHORT-ACTING OPIOID, ON CEREBRAL BLOOD-FLOW, BRAIN ELECTRICAL-ACTIVITY, AND INTRACRANIAL-PRESSURE IN DOGS ANESTHETIZED WITH ISOFLURANE AND NITROUS-OXIDE

Background: A new short-acting opioid, remifentanil, is metabolized by esterase activity in blood and tissue. It is important to know whethe r remifentanil may decrease the time to recovery of opioid-induced car diovascular and cerebral effects compared to that of other short-actin g agents such as alfentanil. Methods: Baseline measures were made duri ng 1% end-tidal isoflurane and 50% N2O in oxygen in dogs. Approximatel y equipotent low- and high-dose remifentanil (0.5 and 1.0 mug . kg-1 . min-1) or alfentanil (1.6 and 3.2 mug . kg-1 . min-1) were infused fo r 30 min each (total infusion time 60 min) followed by a 30-min recove ry period. Blood pressure, heart rate, and intracranial pressure were recorded continuously. Electroencephalogram measurements were made usi ng aperiodic analysis, and regional cerebral blood flow using radioact ive microspheres. Results: Both remifentanil and alfentanil decreased blood pressure and heart rate 25-30%. Cortex, hippocampus, and caudate blood flow decreased 40-50% during opioid infusion, but flow changes in lower brain regions were modest or absent. The electroencephalogram showed a shift from low-amplitude, high-frequency activity during bas eline to high-amplitude, low-frequency activity during opioid infusion . During a 30-min recovery period, heart rate, electroencephalogram, a nd regional cerebral blood flow recovered to baseline levels in remife ntanil- but not in alfentanil-treated dogs. Blood pressure and intracr anial pressure decreased during opioid infusion and increased above ba seline levels during the recovery period in remifentanil-treated dogs. Conclusions: These results show that the cardiovascular and cerebral effects of remifentanil and alfentanil are similar but that recovery o f these parameters occurs sooner following remifentanil.