Remifentanil and nitrous oxide reduce changes in cerebral blood flow velocity in the middle cerebral artery caused by pain

Cerebral blood flow is affected by painful stimuli, and analgesic agents may alter the response of cerebral blood flow to pain. We set out to quantify the effects of remifentanil and nitrous oxide on blood flow changes caused by experimental pain. We simulated surgical pain in 10 conscious volunteers using increasing mechanical pressure to the tibia. We measured changes in cerebral blood flow velocity in the middle cerebral artery (CBFVMCA) caused by the pain, using transcranial Doppler sonography. We gave increasing doses of remifentanil (0.025, 0.05 and 0.1 μg kg−1 min−1) or nitrous oxide [20%, 35% and 50% end-tidal concentration (FE′N2O)] and compared these effects on blood flow changes. Nitrous oxide increased CBFVMCA only when given at 50% FE′N2O. Remifentanil did not affect CBFVMCA. Pain increased CBFVMCA. Both agents attenuated this pain-induced change in CBFVMCA with the exception of nitrous oxide at 20% FE′N2O. Inhalation of nitrous oxide or adminstration of remifentanil attenuated pain-induced changes in CBFVMCA.