The effective concentration 50 (EC50) for propofol with 70% xenon versus 70% nitrous oxide.

Background: Xenon anesthesia has many favorable properties, such as pain modulation and organ protection. However, due to its MAC of 70%, it cannot be used as a sole anesthetic. We estimated the amount of propofol required to supplement xenon to produce adequate anesthesia in 50% and 95% of patients in comparison with nitrous oxide.

Methods: We randomized 75 premedicated female patients to receive either 70% xenon or 70% nitrous oxide in oxygen supplemented by propofol target-controlled infusion anesthesia starting with 4.5 microg/mL for the first patient in each group. Dixon's up and down method was used to determine the propofol concentration for subsequent patients. After induction of anesthesia with propofol, patients breathed 70% xenon or 70% nitrous oxide in oxygen via a facemask for 15 min. They were then observed for movement in response to skin incision for 60 s after the incision and assigned as movers or nonmovers. Probit analysis was used to estimate the effective concentration 50% and 95% (EC50 and EC95) for propofol in both groups.

Results: The EC50 for propofol with 70% xenon was 1.5 microg/mL and the EC95 was 2.3 microg/mL. The EC50 and EC95 values for propofol with nitrous oxide were 2.2 and 8.2 microg/mL, respectively. This implies a reduction of propofol requirements between 32% (EC50) and 72% (EC95) by xenon compared with nitrous oxide. The suppression of auditory evoked potentials was more pronounced with xenon than with nitrous oxide.

Conclusion: Xenon seems to be clinically more potent than nitrous oxide, but still requires minimal supplement of a hypnotic anesthetic to suppress noxious stimulation during and after skin incision.