False IONM signalsare signals recorded during intraoperative neuromonitoring that do not reflect actual nerve damage. These false-positive signals may result from technical artifacts, electrode placement, or device configuration errors, causing unnecessary alarms and concern among the surgical team.
Because false signals may also affect clinical decision-making, correct monitoring practices and interpretation are critically important.
What Are False IONM Signals?
False IONM signals occur when signals obtained during surgery through intraoperative neuromonitoring do not accurately reflect neurological injury.
These signals may trigger alerts due to technical factors, device-related artifacts, or physiological changes, even when no actual nerve damage is present. The signals must therefore be evaluated alongside surgical and anesthetic findings.
Common Technical Causes of False IONM Signals
Technical causes of false IONM signals include artifacts related to inadequate electrode insulation, electromagnetic interference, and inappropriate device parameters.
These factors may cause signal fluctuations or false alarms without actual neurological changes. Appropriate technical settings and high-quality signals are therefore important for reliable monitoring.
Electrode Placement and Impedance Problems
Incorrect electrode placement or inadequate tissue contact may reduce IONM signal quality and increase impedance, leading to signal loss or artifacts.
Impedance reflects the electrical contact between the electrode and tissue. High impedance usually indicates poor conduction and makes reliable signal acquisition difficult. Balanced impedance values in the range of 2–5 kΩ are generally targeted. Appropriate checks of electrode placement and impedance are therefore critical for signal accuracy.
Anesthesia-Related Signal Changes
Anesthetic drugs, especially inhalational anesthetics, may reduce MEP and SSEP amplitudes and cause signal loss. These changes depend on the depth of anesthesia and the type of agent, and may complicate signal interpretation.
Total intravenous anesthesia (TIVA) is therefore often preferred during IONM. In the event of sudden signal changes, anesthesia-related effects must be reviewed before surgical intervention.
How Can False Signals Be Prevented in Intraoperative Neuromonitoring?
To prevent false signals, technical factors such as electrode placement, device settings, and patient positioning should be checked carefully.
Continuous communication between the surgical and neurophysiology teams, together with real-time signal assessment, is also necessary. Standardized protocols and appropriate anesthetic techniques help reduce false alarms.
In practice, promptly checking electrodes, anesthesia, and stimulation parameters after sudden signal changes is an important step in identifying false alarms.
Frequently Asked Questions
- How can a false IONM signal be distinguished from actual nerve damage?
Technical factors and anesthetic status are checked promptly, and the findings are evaluated alongside the surgical procedure. - Can anesthesia cause false IONM signals?
Yes, inhalational agents in particular can reduce signal amplitude. - Can false signals be completely prevented?
No, but their frequency can be significantly reduced with appropriate protocols.
References
- MacDonald, D. B. (2006). Intraoperative motor evoked potential monitoring: Overview and update. Journal of Clinical Monitoring and Computing, 20(5), 347–377.
- Skinner, S. A., & Holdefer, R. N. (2014). Intraoperative neuromonitoring: Technical aspects and common pitfalls. Neurosurgical Focus, 37(5), E7.
- Sutter, M., Eggspuehler, A., Grob, D., et al. (2007). The influence of anesthesia on intraoperative neuromonitoring signals. Spine, 32(22), 2365–2371.
- Nuwer, M. R., Emerson, R. G., Galloway, G., et al. (2012). Evidence-based guideline update: Intraoperative spinal monitoring. Neurology, 78(8), 585–589.