Low-dose remifentanil increases regional cerebral blood flow and regional cerebral blood volume, but decreases regional mean transit time and regional cerebrovascular resistance in volunteers

We have used contrast media-enhanced perfusion magnetic resonance imaging M RI to measure regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT) and regional cerebrovascul ar resistance (rCVR) in volunteers at baseline and during infusion of remif entanil (0.1 mu g kg(-1) min(-1)). Remifentanil increased rCBF and rCBV in white and grey matter (striatal, thalamic, occipital, parietal, frontal) re gions, with a parallel decrease in rMTT in those regions with the exception of occipital grey matter. rCVR was decreased in all regions studied. The r elative increase in rCBF was greater than that in rCBV. Cerebral haemodynam ics were increased significantly in areas less rich in mu-opioid receptors with a tendency towards more pronounced increases in rCBF and rCBV in pain- processing areas. Furthermore, interhemispheric differences in rCBF, rCBV a nd rMTT found prior to drug administration were almost eliminated during in fusion of remifentanil. We conclude that, apart from direct and indirect ce rebrovascular effects of remifentanil, these findings are consistent with c erebral excitement and/or disinhibition.