Thiopental pharmacodynamics. I. Defining the pseudo-steady-state serum concentration-EEG effect relationship

Area of Science:

• Anesthesiology and Pharmacology
• Neuroscience and Brain Monitoring

Background:

• Assessing anesthesia depth requires stable drug serum concentrations for consistent central nervous system effects.
• Electroencephalogram (EEG) monitoring provides a measure of drug effect on the brain.

Purpose of the Study:

• To utilize a computer-controlled infusion pump (CCIP) for achieving constant serum thiopental concentrations.
• To employ EEG as an indicator of thiopental's central nervous system effect.
• To characterize the concentration-response relationship between serum thiopental and EEG activity.

Main Methods:

• A CCIP was used in six male volunteers to rapidly achieve and maintain target serum thiopental concentrations (10-40 µg/ml) for 6-minute intervals.
• Aperiodic waveform analysis measured EEG frequency (waves per second) as a marker of thiopental's effect.
• Pharmacodynamic modeling was used to describe the concentration-response relationship.

Main Results:

• The CCIP demonstrated good performance, with a median bias of +5% and median absolute error of 16% in maintaining target thiopental concentrations.
• EEG stabilized within 2-3 minutes of serum concentration changes and remained constant.
• A biphasic concentration-response curve was observed, with peak EEG activation at 13.3 µg/ml and return to baseline at 31.2 µg/ml.

Conclusions:

• CCIPs enable rapid achievement and maintenance of stable serum thiopental concentrations.
• The study successfully characterized the concentration-dependent EEG effects of thiopental.
• This method allows for precise assessment of anesthesia depth using EEG monitoring.