Cerebral blood flow and CO2 reactivity is similar during remifentanil/N2O and fentanyl/N2O anesthesia

Background: Remifentanil, a rapidly metabolized Er-opioid agonist, may offer advantages for neurosurgical procedures in which prolonged anesthetic effects can delay assessment of the patient, This study compared the effects of remifentanilnitrous oxide on cerebral blood flow (CBF) and carbon dioxide reactivity with those of dentanyl-nitrous oxide anesthesia during craniotomy. Methods: After institutional approval and informed patient consent were obtained, 23 patients scheduled to undergo supratentorial tumor surgery were randomly assigned to remifentanil or fentanyl infusion groups in a double-blinded manner. Midazolam, thiopental, and pancuronium induction was followed by equipotent narcotic loading infusions of remifentanil (1 mu g.kg(-1).min(-1)) or fentanyl (2 mu g.kg(-1).min(-1)) for 5-10 min. Patients were ventilated with 2:1 nitrous oxide-oxygen, and opioid rates were reduced and then titrated to a stable hemodynamic effect, After dural exposure, CBF was measured by the intravenous (133)xenon technique at normocapnia and hypocapnia. Reactivity of CBF to carbon dioxide was calculated as the absolute increase in CBF; per millimeters of mercury increase in the partial pressure of carbon dioxide (Pa-CO2). Data were analyzed by repeated-measures analysis of variance, unpaired Student's t tests, or contingency analysis. Results: In the remifentanil group (n = 10), CBF decreased from 36 +/- 11 to 27 +/- 8 ml.100 g(-1). min(-1) as Pa-CO2 decreased from 33 +/- 5 to 25 +/- 2 mmHg. In the fentanyl group (n = 8), CBF decreased from 37 +/- 11 to 25 +/- 6 ml.100 g(-1).min(-1) as Pa-CO2 decreased from 34 +/- 3 to 25 +/- 3 mmHg. Absolute carbon dioxide reactivity was preserved with both agents: 1 +/- 1.2 ml.100 g(-1).min(-1).mmHg(-1) for remlfentanil and 1.5 +/- 0.5 ml.100 g-(1.)min(-1).mmHg(-1) for fentanyl (P = 0.318). Conclusion: Remifentanil and fentanyl have similar effects on absolute CBF, and cerebrovascular carbon dioxide reactivity is maintained.