INTACT CEREBRAL BLOOD-FLOW REACTIVITY DURING REMIFENTANIL NITROUS-OXIDE ANESTHESIA

Remifentanil hydrochloride is a new opioid rapidly metabolized. by blo od and tissue esterases. The swift degradation accounts for the elimin ation half-life (t(1/2) beta) of <10 min, An anesthetic agent allowing more rapid postoperative assessment of the neurosurgical patient woul d be beneficial, This study examined the effect of remifentanil on cer ebral blood flow (CBF) reactivity to changes in the arterial partial p ressure of carbon dioxide (PaCO2). Cerebral blood flow was measured wi th intravenous 133-Xenon during remifentanil/ nitrous oxide (N2O) anes thesia in IO patients undergoing: craniotomy. Cerebrovascular reactivi ty was determined by repeating CBF measurements after the addition of carbon dioxide (CO2) to the inspired gas mixture, The CBF increased fr om 21 +/- 6 to 31 +/- 7 ml/100 g/min as the PaCO2 increased from 27 +/ - 4 to 36 +/- 3 mm Hg, The relative CBF reactivity was 3.6 +/- 1.2 %/m m Hg CO2. During the CBF determinations, the doses of remifentanil adm inistered were not significantly different (0.38 +/- 0.18 mu g/kg/min at hypocapnia vs. 0.34 +/- 0.16 mu g/kg/min at normocapnia). Electroen cephalographic monitoring showed a spectral edge frequency of 26 +/- 1 Hz before induction, 25 +/- 1 Hz during maintenance of the remifentan il/N2O anesthetic (0.32 +/- 0.15 mu g/kg/min min), 24 +/- I Hz during hypocapnic CBF determination, and 24 +/- 2 Hz during normocapnic CBF d etermination, At the completion of the procedure, the patients respond ed to commands within 3.6 +/- 2.5 min and were extubated 7.2 +/- 4.5 m in after the remifentanil/N2O was discontinued. In conclusion, absolut e CBF values during remifentanil/N2O are similar to previously reporte d CBF values during fentanyl/N2O and isoflurane/N2O anesthesia, and ce rebrovascular reactivity to CO2 remains intact.