Can remifentanil replace nitrous oxide during anesthesia for ambulatory orthopedic surgery with desflurane and fentanyl

BACKGROUND: The administration of nitrous oxide (N 2 O) may be associated with side effects and toxicities. Remifentanil shares characteristics with N 2 O, including MAC-reducing and antinociceptive effects and a rapid decrease in clinical effect when discontinued. We compared the outcome after ambulatory orthopedic surgery with desflurane and fentanyl supplemented with clinically equivalent doses of either N 2 O or remifentanil. METHODS: Seventy patients undergoing ambulatory orthopedic surgery were studied. Thirty-five received 66% N 2 O and 35 received remifentanil 0.085 μg·kg -1 ·min -1 in addition to desflurane, titrated to a bispectral index (BIS) value of 50, and a fentanyl infusion. The principle outcome measure was time to awakening to verbal stimulation. Secondary outcome measures included neuropsychological testing, time to orientation, hemodynamic values, pain and nausea visual analog scores, discharge times, and satisfaction scores. The average end-tidal desflurane concentration and fentanyl effect-site concentration were determined. RESULTS: The median time (interquartile range) to awakening to verbal stimulation, 3.0 min (3.0-5.0 min) in the remifentanil group and 4.6 min (3.0-8.1 min) in the N 2 O group was not significantly different. Median time to orientation was significantly faster in the remifentanil group: 6.0 min (5.0-8.5 min) compared with 8.0 min (5.0-12.8 min) for the N 2 O group. There was no difference between groups in desflurane or fentanyl administration, neuropsychological testing, or any other outcome measure. CONCLUSIONS: This study demonstrates that a remifentanil infusion of 0.085 μg·kg -1 ·min -1 may be substituted for 66% N 2 O during desflurane/fentanyl anesthesia without any clinically significant change in outcome.