Effective concentration 50 for propofol with and without 67% nitrous oxide

Area of Science:

• Anesthesiology
• Pharmacology
• Clinical Trials

Background:

• Propofol is a widely used anesthetic agent.
• Understanding its effective concentration (EC) is crucial for safe and effective anesthesia.
• The influence of co-administered agents like nitrous oxide on propofol's EC requires further investigation.

Purpose of the Study:

• To determine the effective blood concentration (EC) of propofol required to prevent response to surgical incision.
• To compare the EC of propofol when administered alone versus with nitrous oxide.
• To validate microcomputer-predicted propofol concentrations against measured values.

Main Methods:

• Sixty-five ASA I or II female patients received propofol via a microcomputer-controlled infusion system.
• Patients breathed either 100% oxygen or 67% nitrous oxide in oxygen.
• Response to surgical incision was assessed, and probit analysis was used to determine EC50 values.

Main Results:

• The predicted EC50 for propofol/N2O/O2 was 4.5 µg/mL, and for propofol/O2 was 6.0 µg/mL.
• The measured EC50 for propofol/N2O/O2 was 5.36 µg/mL, and for propofol/O2 was 8.1 µg/mL.
• Nitrous oxide reduced the predicted EC50 by 25% and the measured EC50 by 33%.

Conclusions:

• The co-administration of 67% nitrous oxide significantly reduces the effective blood concentration of propofol.
• Predicted EC values may better reflect equilibrated central compartment concentrations than measured values during infusion.
• Microcomputer-controlled infusion systems aid in precise propofol delivery and EC determination.