Intact cerebral blood flow reactivity during remifentanil/nitrous oxide anesthesia

Remifentanil hydrochloride is a new opioid rapidly metabolized by blood and tissue esterases. The swift degradation accounts for the elimination half-life (t1/2 beta) of < 10 min. An anesthetic agent allowing more rapid postoperative assessment of the neurosurgical patient would be beneficial. This study examined the effect of remifentanil on cerebral blood flow (CBF) reactivity to changes in the arterial pressure of carbon dioxide (PaCO2). Cerebral blood flow was measured with intravenous 133-Xenon during remifentanil/ nitrous oxide (N2O) anesthesia in 10 patients undergoing craniotomy. Cerebrovascular reactivity was determined by repeating CBF measurements after the addition of carbon dioxide (CO2) to the inspired gas mixture. The CBF increased from 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%/mm Hg CO2. During the CBF determinations, the doses of remifentanil administered were not significantly different (0.38 +/- 0.18 microgram/kg/min at hypocapnia vs. 0.34 +/- 0.16 microgram/kg/min at normocapnia). Electroencephalographic monitoring showed a spectral edge frequency of 26 +/- 1 Hz before induction, 25 +/- 1 Hz during maintenance of the remifentanil/N2O anesthetic (0.32 +/- 0.15 microgram/kg/ min), 24 +/- 1 Hz during hypocapnic CBF determination, and 24 +/- 2 Hz during normocapnic CBF determination. At the completion of the procedure, the patients responded to commands within 3.6 +/- 2.5 min and were extubated 7.2 +/- 4.5 min after the remifentanil/N2O was discontinued. In conclusion, absolute CBF values during remifentanil/N2O are similar to previously reported CBF values during fentanyl/N2O and isoflurane/N2O anesthesia, and cerebrovascular reactivity to CO2 remains intact.