A novel method of deriving the effect compartment equilibrium rate constant for propofol

Area of Science:

• Pharmacology
• Anesthesiology
• Pharmacokinetics

Background:

• Calculating propofol effect compartment concentration (Ce) in non-steady-state conditions necessitates the equilibrium rate constant (keo).
• Traditional keo derivation for propofol relies on electroencephalogram (EEG) measurements.
• This study explored an alternative method for determining keo.

Purpose of the Study:

• To investigate an alternative method for deriving the equilibrium rate constant (keo) for propofol.
• To determine if keo can be calculated without using electroencephalogram (EEG) monitoring.
• To ensure consistent predicted effect compartment concentration (Ce) across different propofol administration methods.

Main Methods:

• Seventy-five patients undergoing anesthesia induction received propofol via single bolus, infusion, or bolus-then-infusion.
• Computer simulation was employed to predict central compartment concentration.
• The keo was derived by ensuring the predicted Ce at loss of the eyelash reflex remained consistent across the three administration methods.

Main Results:

• The derived keo was 0.80 min⁻¹.
• The mean (SD) effect compartment concentration (Ce) at loss of the eyelash reflex was 2.27 (0.69) µg mL⁻¹.
• Consistent Ce values were achieved at the pharmacodynamic endpoint regardless of administration method.

Conclusions:

• The effect compartment equilibrium rate constant (keo) can be determined without electroencephalogram (EEG) monitoring.
• The propofol concentration at loss of the eyelash reflex can be accurately estimated using this alternative method.
• This approach simplifies the determination of key pharmacokinetic parameters in anesthesia.