D-Wave Stimulation Artifact Interfering with BIS Monitoring During Intradural Extramedullary Tumor Excision: A Practical Concern

The bispectral index (BIS) monitor is widely used to assess depth of anesthesia, particularly during total intravenous anesthesia (TIVA). We report a limitation observed during intraoperative D-wave monitoring for intradural extramedullary (IDEM) tumor excision under TIVA without neuromuscular blockade.

Between January 2024 and May 2025, 14 IDEM tumor excisions were performed with intraoperative D-wave monitoring using the NIM-Eclipse E-4 system (Medtronic, United States) with the electrode placed one level caudal to dural opening ([Supplementary Fig. S1], available in online version only). Continuous single-pulse transcranial stimulation at 1 Hz was employed. In every case, stimulation produced a high-voltage artifact at the same frequency in the BIS-processed electroencephalographic (EEG) waveform ([Fig. 1]). This was visually disruptive and consistently prevented BIS computation. Since TIVA is often combined with D-wave and motor evoked potential monitoring, reliable EEG-based depth assessment becomes essential.[1] Artifact contamination thus rendered BIS monitoring unreliable at precisely the period when it was most needed.

Fig. 1 BIS-processed EEG waveform displaying high-voltage artifacts (indicated by arrow) corresponding to 1 Hz D-wave stimulation during intraoperative neuromonitoring. The artifact results in a BIS Signal Quality Index (SQI) of 0 and elevated electromyographic (EMG) activity (75%), leading to failure of BIS value computation. EEG, electroencephalography.

To mitigate this issue, we increased the stimulation frequency to 2 Hz in a 55-year-old woman undergoing IDEM excision at D9 to D12 (SDC 1). This was based on the assumption that BIS and NIM Eclipse filters (typically 0.5–1 Hz) would attenuate artifacts below this cutoff, preserving higher frequency EEG for spectral edge frequency computation.[2] Contrary to expectation, the BIS monitor continued to show artifacts, now at 2 Hz, while failing to compute the index, and the NIM Eclipse EEG trace was entirely lost. This adjustment was repeated in subsequent cases, but artifacts persisted. We also attempted higher high-pass filter settings (≥2 Hz) on the NIM Eclipse in one case; the artifact persisted, confirming that pulse amplitude rather than frequency alone was the major contributor.

The mechanism lies in the nature of D-wave stimulation. Although repeated at 1 Hz, each pulse is a short, high-voltage impulse with wide frequency content. By Fourier theory, such impulses contain harmonics across the EEG spectrum, and their large amplitude saturates multiple frequency bands simultaneously.[2] As a result, BIS input channels are overwhelmed and the algorithm, despite using spectral separation methods, rejects the signal once artifact thresholds are exceeded. This explains why neither filter adjustments nor frequency shifts restored reliable computation.

It is well known that electrical stimulation can contaminate EEG.[3] For example, electrocautery generates continuous high-frequency interference that BIS may misinterpret as beta/gamma EEG, producing spuriously high BIS values even during deep anesthesia. By contrast, D-wave stimulation produces discrete, high-amplitude broadband impulses that overwhelm the system and result in complete loss of BIS computation. Both represent limitations of processed EEG monitoring, but the mechanism and consequences differ: electrocautery risks anesthetic overtitration through falsely high BIS values,[4] whereas D-wave monitoring deprives the clinician of depth information altogether. Moreover, electrocautery artifacts are typically intermittent, allowing BIS monitoring to resume once cautery is suspended, while D-wave stimulation is delivered continuously for the duration of decompression, leaving no interruption-free window for depth assessment.

Vaithialingam et al recently reported similar artifacts in BIS traces during D-wave monitoring and suggested using these as surrogate confirmation of stimulus delivery.[5] While this may reassure neurophysiologists, it compromises the anesthesiologist's ability to assess depth—an arguably more critical function during long spinal tumor resections. Dedicated neuromonitoring platforms such as NIM Eclipse already confirm stimulus delivery, making BIS artifact recognition redundant.

While artifacts from electrocautery and other electrical devices are well recognized and frequently reported, interference from D-wave stimulation remains highly underreported despite being consistently encountered in practice. Our observation underscores the importance of reporting such artifacts, not only to improve awareness among clinicians but also to drive advancements in EEG-based depth monitoring algorithms and hardware design.[6] Highlighting these limitations is essential if we are to refine neuromonitoring strategies and ensure reliable anesthesia depth assessment during complex spinal procedures.

Conflict of Interest

None declared.

• References

• 1 Nimmo AF, Absalom AR, Bagshaw O. et al. Guidelines for the safe practice of total intravenous anaesthesia (TIVA): Joint Guidelines from the Association of Anaesthetists and the Society for Intravenous Anaesthesia. Anaesthesia 2019; 74 (02) 211-224
• 2 Rampil IJ. A primer for EEG signal processing in anesthesia. Anesthesiology 1998; 89 (04) 980-1002
• 3 Dahaba AA. Different conditions that could result in the bispectral index indicating an incorrect hypnotic state. Anesth Analg 2005; 101 (03) 765-773
• 4 Hemmerling TM, Desrosiers AM. Interference of electromagnetic operating systems in otorhinolaryngology surgery with bispectral index monitoring. Anesth Analg 2003; 96 (06) 1698-1699
• 5 Vaithialingam B, Masapu D, Rudrappa S. Stimulation artefact on EEG trace with BIS monitoring during D-wave recording. J Clin Monit Comput 2023; 37 (03) 929-931
• 6 Chan MTV, Ho SS, Gin T. Performance of the bispectral index during electrocautery. J Neurosurg Anesthesiol 2012; 24 (01) 9-13

Publikationsverlauf

Artikel online veröffentlicht:
12. Dezember 2025