Interaction between nitrous oxide, sevoflurane, and opioids: a response surface approach

Area of Science:

• Anesthesiology
• Pharmacology
• Mathematical Modeling

Background:

• The hierarchical model describes sevoflurane-opioid interactions.
• This study expands the model to include 66% nitrous oxide (N2O).
• Data analyzed includes motor/hemodynamic responses, MAC, and MAC-BAR.

Purpose of the Study:

• To expand the hierarchical model for combined sevoflurane, opioid, and N2O administration.
• To quantify the interaction effects of N2O with sevoflurane and opioids.
• To develop a predictive model for anesthetic responses.

Main Methods:

• Postulated four actions of N2O: additive or potency-reducing effects with fentanyl and sevoflurane.
• Fitted models using NONMEM software.
• Assumed identical interaction parameters for movement and sympathetic responses.

Main Results:

• 66% N2O showed an additive effect equivalent to 0.27 ng/ml fentanyl (Parameter A).
• 66% N2O also showed an additive effect equivalent to 0.54 vol.% sevoflurane (Parameter X).
• Potency-reducing effects (Parameters B and Y) did not improve model fit.

Conclusions:

• N2O's effect integrates into the hierarchical model via simple extension.
• The model accurately predicts movement and sympathetic responses.
• This facilitates understanding of combined anesthetic agent interactions.