Motor-evoked potential facilitation during progressive cortical suppression by propofol

Area of Science:

• Neuroscience
• Anesthesiology
• Biomedical Engineering

Background:

• Propofol is a common anesthetic agent affecting cortical excitability.
• Transcranial magnetoelectric stimulation (TMES) is a technique used to modulate cortical activity.
• Understanding the impact of anesthesia on neurostimulation is crucial for patient safety.

Purpose of the Study:

• To investigate the effects of different TMES patterns on motor-evoked potentials (MEPs) under varying propofol-induced cortical suppression.
• To determine optimal TMES parameters for eliciting MEPs at different levels of anesthesia.

Main Methods:

• Twenty patients undergoing lumbar disk surgery received incrementally increasing propofol target plasma concentrations (PTPCs).
• Motor-evoked potentials (MEPs) were recorded from upper extremity muscles.
• Single, double, and quadruple TMES at 100, 200, and 500 Hz were applied.

Main Results:

• At PTPCs <3 microg/mL, quadruple TMES at 100 Hz elicited maximal MEP amplitudes.
• At PTPCs >=3 microg/mL, quadruple TMES at 200 Hz yielded peak MEP amplitudes.
• The optimal stimulation frequency shifted from 100 Hz to 200 Hz as propofol concentration increased.

Conclusions:

• The optimal frequency for TMES-induced MEPs shifts with increasing propofol levels.
• This shift may be due to propofol's dose-dependent action on cortical interneurons.
• Further research using spinal cord evoked potentials can elucidate anesthesia's modulatory effects on intracortical facilitation.