[Interference between M-Entropy and Thermistor Probe Fixed on the Forehead during General Anesthesia]

Area of Science:

• Anesthesiology
• Biomedical Engineering
• Neuroscience

Background:

• Accurate monitoring of anesthesia depth is crucial for patient safety.
• M-Entropy is a processed electroencephalogram (EEG) index used to assess anesthetic depth.
• Tissue-core thermometers are commonly used for intraoperative temperature monitoring.

Observation:

• A patient undergoing forearm fracture surgery experienced sudden, extremely high M-Entropy values.
• Simultaneously, raw EEG showed slow waves and sleep spindles, inconsistent with high entropy.
• Vital signs remained stable despite the reported high entropy levels.

Findings:

• The M-Entropy artifact was directly linked to the placement of a Coretemp® tissue-core thermometer probe on the forehead.
• Removing the probe immediately normalized M-Entropy readings.
• The interference was reproducible by attaching and detaching the probe, indicating electrical noise as the cause.

Implications:

• Electrical interference from medical devices can artifact EEG-based monitors like M-Entropy.
• Clinicians must correlate monitor data with raw EEG waveforms and clinical status to accurately assess anesthesia depth.
• Careful placement and consideration of potential device interactions are necessary during surgery.