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CC BY 4.0 · J Neuroanaesth Crit Care
DOI: 10.1055/s-0045-1809409
Case Series

Utility of Bispectral Index Monitor as a Tool to Detect and Manage Intraoperative Seizure: A Case Series

Sandeep Dey 
1   Department of Neuroanaesthesia and Neurocritical Care, Paras Health, Gurugram, Haryana, India
,
Megha Tyagi
1   Department of Neuroanaesthesia and Neurocritical Care, Paras Health, Gurugram, Haryana, India
,
Amit Goyal 
1   Department of Neuroanaesthesia and Neurocritical Care, Paras Health, Gurugram, Haryana, India
,
Pallav Kumar
1   Department of Neuroanaesthesia and Neurocritical Care, Paras Health, Gurugram, Haryana, India
› Author Affiliations
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Abstract

Conventional electroencephalogram (EEG) has been the most common method to detect and manage seizure episodes. Limitations to its use in the intraoperative period during neurosurgical cases have made detecting intraoperative seizure almost impractical, especially in the presence of a neuromuscular blocking agent. Using an EEG-based monitor like bispectral index (BIS) can add a new dimension to intraoperative neuromonitoring in patients at risk of seizure. Apart from other indices, it also displays the real-time raw EEG waveform, which can be valuable in diagnosing an intraoperative seizure and guide the therapeutic achievement of burst suppression. An increase in the BIS value has also been reported during intraoperative seizures. Here, we present the cases of three patients posted for excision of intracranial space-occupying lesions who developed intraoperative seizures, which were diagnosed and managed with the aid of a BIS monitor. This case series highlights the utility of BIS in detecting and managing intraoperative seizures, apart from its role in depth of anesthesia monitoring.


 

Keywords

bispectral index - burst suppression - depth of anesthesia - electroencephalogram - Intraoperative seizure

Introduction

Seizure is a common manifestation of brain tumors with a reported incidence as high as 30 to 100%.[1] Around 20 to 50% of patients with supratentorial meningioma present with seizure as the only symptom before being diagnosed radiologically.[2] In addition, patients may present with seizures for the first time during the intraoperative period. Various risk factors for intraoperative seizures include previous history of seizure, low grade lesions, frontal or temporal lobe lesions, and transcranial motor evoked potential monitoring.[3] [4] Though the exact incidence of intraoperative seizure under general anesthesia is not known, the reported incidence lies between 1.8 and 2.3% among patients undergoing motor evoked potential monitoring or elective supratentorial craniotomy.[4] [5] Intraoperative seizures can lead to brain bulge, increased cerebral metabolic oxygen demand, hypoxic brain damage, and hemodynamic instability. Moreover, if undetected, they can delay the emergence from anesthesia. Therefore, early detection and prompt termination are crucial. Conventional electroencephalogram (EEG) has limitations in the intraoperative period, which hinders the operative field. Bispectral index (BIS) can add a new dimension to intraoperative neuromonitoring in patients at risk of seizure. Apart from indices for the depth of anesthesia monitoring, it also displays the real-time raw EEG waveform, thus contributing to the diagnosis of intraoperative seizure, and guiding the therapeutic achievement of burst suppression. Its placement on the forehead also does not interfere with the operative field. Our case series illustrates how BIS, along with its raw EEG display, can facilitate early detection and management of intraoperative seizures.


 

Anesthesia Protocol

To facilitate the intraoperative evoked potential monitoring, total intravenous anesthesia with propofol target-controlled infusion (TCI) (3 mcg/mL) and fentanyl (3–4 mcg/kg) was used for induction and propofol (TCI titrated to target BIS value) with dexmedetomidine (0.5 mcg/kg/hr) and ketamine (0.25 mg/kg/hr) infusion was used for maintenance of anesthesia. Rocuronium (1 mg/kg) was used as a single bolus to aid the endotracheal intubation. A scalp block with 15 mL of 0.2% ropivacaine and 4 mg dexamethasone was performed prior to the Mayfield head frame application. Along with standard intraoperative monitoring, a frontal BIS electrode (BIS Quatro Sensor, Medtronic, India) was applied on the contralateral forehead to monitor the depth of anesthesia with a target BIS value of 40 to 60.

Case 1

A 66-year-old female of American Society of Anesthesiology class 2 with right suprasellar and left temporal meningioma was scheduled for elective craniotomy and excision of both lesions under evoked potential monitoring. She did not have any previous seizure history. During surgical wound closure, prior to any reduction in depth of anesthesia (TCI effect site concentration 2.7 mcg/mL) there was a sudden spike in BIS value from 40 to 45 to 85 to 95 ([Fig. 1A]) along with appearance of high-amplitude waves followed by generalized tonic-clonic seizure (GTCS), which was terminated using midazolam 4 mg and propofol bolus, leading to electrographic supersession on BIS. The seizure activity was concurrent with a sharp rise in EtCO2 (> 50), blood pressure ([Fig. 1A]), and changes in arterial blood gas (ABG) (raised PaCO2 and lactate levels with normal blood sugar level). Any increase in the BIS electrode impedance was also ruled out. The patient also received an additional dosage of levetiracetam 1.5 g. Subsequently, no seizure activity was noted in the postoperative period, and the patient was extubated on the next day in the intensive care unit (ICU) with uneventful further recovery.

Zoom
Fig. 1 Image showing intraoperative vitals trends of cases 1 and 2. (A) Case 1 with black arrow showing rise in EtCO2, white arrow showing rise in bispectral index (BIS) value on vital trends, and red arrow showing suppression of electrographic activity on raw electroencephalogram (EEG). (B) Case 2 with red arrow showing high-amplitude, low-frequency waveform pattern on raw EEG during intraoperative seizure.

 

Case 2

A 51-year-old female presented for resection of left parieto-occipital parasagittal meningioma without any history of previous seizures. Following craniotomy and prior to dura opening without any reduction in the depth of anesthesia (propofol TCI effect site concentration 3 mcg/mL), the patient developed GTCS, which was associated with a rise in BIS value followed by the appearance of high-amplitude, low-frequency waveform on the raw EEG ([Fig. 1B]). It was terminated using midazolam 4 mg and burst suppression on BIS using propofol bolus. The rest of the intraoperative period was uneventful, and the patient was extubated in the evening on the same day when fully awake.


 

Case 3

A 70-year-old male with renal cell carcinoma and secondary right parietal brain metastasis was scheduled for craniotomy and resection of the lesion under evoked potential monitoring. Intraoperatively, during resection of the lesion, there was the appearance of high-amplitude waves with a sudden spike in the BIS value ([Fig. 2A] and [B]), followed by clinically evident GTCS and associated brain bulge, hypertension, tachycardia, and hypercarbia ([Fig. 2B]). Any decrease in the depth of anesthesia (TCI effect site concentration 3.0 mcg/mL) or increase in the BIS electrode impedance was also ruled out. The seizure was terminated immediately using midazolam 4 mg and propofol bolus, followed by an additional dose of levetiracetam. Brain bulge was also settled following head-end elevation, hyperventilation, and electrographic suppression of BIS. ABG showed a normal metabolic profile with low PaCO2 secondary to hyperventilation. The subsequent perioperative period was uneventful, and the patient was extubated on the same day in the ICU upon regaining complete consciousness.

Zoom
Fig. 2 Image showing intraoperative vital with trend in case 3. (A) Red arrow shows rise in bispectral index (BIS) value and white arrow shows electrographic activity in raw electroencephalogram (EEG). (B) Black arrow showing rise in EtCO2 and red arrow showing rise in BIS trend, and blue arrow show suppression of electrographic activity.

 

 

Discussion

Conventional methods to detect seizures have relied mainly upon continuous EEG monitoring.[6] However, they have limitations of bulky setup, low temporal or spatial resolution, power line interference, and most importantly, hindrance in the operative field.[6] Therefore, intraoperative seizure has been an underdetected or underreported event in literature.

BIS is an EEG-based algorithm to monitor the depth of anesthesia. Apart from other indices, it also displays the real-time raw EEG waveform.[7] Although the EEG is reflective of a selected part of the hemicranium, it can be valuable in the diagnosis of an intraoperative seizure using various waveform patterns such as spikes, spike-wave, and poly-spike patterns, as well as to guide the therapeutic achievement of burst suppression.[8] An increase in the BIS value during intraoperative seizure has also been reported, which may result from an increase in the high amplitude and frequency component of EEG.[9] [10] This increase in BIS could also be a result of increased electromyographic (EMG) activity; however, increased BIS value in the presence of neuromuscular blockade has also been reported previously.[11] [12] [13] In addition, EMG activity can reduce the probability of encountering classical patterns of epileptogenic waveform. Iturri Clavero et al and Srinivas et al reported high-amplitude waves during intraoperative seizures similar to our case, which disappeared after antiepileptic drug administration.[9] [10] A higher BIS/SR (suppression ratio) has been used to differentiate epileptic and normal bursts in patients with refractory status epilepticus under propofol sedation.[14]

Various anesthetic agents have variable effects on seizure threshold and BIS value at different doses. Ketamine is considered proepileptic, but when given along with propofol, it has antiepileptic properties. Ketamine bolus may also increase BIS value, which occurs several minutes after administration. However, this effect on BIS is not seen when ketamine is administered as a slow infusion under propofol TCI anesthesia.[15] Dexmedetomidine has also been shown to reduce seizure threshold in rat models, but this effect has not been noted in humans.[16]

Although BIS monitor is not Food and Drug Administration-approved as a diagnostic tool for seizures, BIS value, along with the understanding of raw EEG, can prove useful during the intraoperative period for the diagnosis of nonconvulsive status epilepticus or seizures in the presence of neuromuscular blocking agents (NMBAs), especially when used with bilateral montage.[13] [17] [18] [19] In addition, concurrent disturbances in hemodynamics and metabolic profile may aid in the diagnosis. Our patients did not experience significant hemodynamic disturbances, probably due to the dexmedetomidine infusion. But, in the absence of a change in depth of anesthesia, changes in raw EEG and metabolic profile, along with the reversal of waveform with antiepileptic medications, favor the diagnosis of intraoperative seizure. The high-amplitude and low-frequency EEG patterns seen during the intraoperative seizure in our cases have not been widely reported. Our cases emphasize that while these findings are preliminary, they add evidence to the role of BIS beyond anesthetic depth and could improve intraoperative safety by facilitating prompt detection and treatment of seizures. However, BIS has certain limitations, such as limited spatial resolution compared with multilead EEG and false positive increase (due to EMG interference or anesthetic depth fluctuations). In the absence of a large data or case reports, larger multicenter studies focusing on EEG changes in the presence or absence of NMBA, along with the effect of various anesthetic agents on intraoperative EEG and the development of BIS software optimized for seizure detection, are required to validate the findings.


 

Conclusion

Intraoperative seizure is an unwanted event with possible deleterious consequences. Due to the inability to use conventional EEG during neurosurgical procedures, BIS, along with raw EEG display, can facilitate early detection and management of intraoperative seizures.


 

 

Conflict of Interest

None declared.

Ethical Approval

Institutional ethical approval and consent for publication were obtained from patients.



Address for correspondence

Sandeep Dey, MD
Flat A 102, Sanskriti Appartment, Sector 43, Gurugram, Haryana, 122002
India   

Publication History

Article published online:
16 July 2025

© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)

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Zoom
Fig. 1 Image showing intraoperative vitals trends of cases 1 and 2. (A) Case 1 with black arrow showing rise in EtCO2, white arrow showing rise in bispectral index (BIS) value on vital trends, and red arrow showing suppression of electrographic activity on raw electroencephalogram (EEG). (B) Case 2 with red arrow showing high-amplitude, low-frequency waveform pattern on raw EEG during intraoperative seizure.
Zoom
Fig. 2 Image showing intraoperative vital with trend in case 3. (A) Red arrow shows rise in bispectral index (BIS) value and white arrow shows electrographic activity in raw electroencephalogram (EEG). (B) Black arrow showing rise in EtCO2 and red arrow showing rise in BIS trend, and blue arrow show suppression of electrographic activity.