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 Table of Contents  
Year : 2022  |  Volume : 1  |  Issue : 2  |  Page : 77-79

Intraoperative electrocardiogram monitoring induced bispectral index interference – A misleading heart–mind connection

Department of Anesthesiology, Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly, Uttar Pradesh, India

Date of Submission16-Aug-2022
Date of Decision21-Oct-2022
Date of Acceptance23-Oct-2022
Date of Web Publication02-Dec-2022

Correspondence Address:
Dr. Akhilesh Pahade
Department of Anesthesiology, Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly - 243 202, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jica.jica_24_22

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Bi-spectral index (BIS) is a common but an important tool in anaesthesiologist's armamentarium across the world which helps to assess the level of sedation and effect of hypnotic drugs. A value between 40-60 in BIS is considered as optimal level of sedation during general anaesthesia. However, numerous factors can interfere with accurate BIS value. Electrocardiogram (ECG), has been mentioned as a factor resulting into fallacious BIS values in the literature, which may have significant implications on appropriate dosage of hypnotic drugs. ECG inferences are usually filtered by proprietary algorithm of BIS, and few cases have been documented wherein ECG interference resulted in fallacious BIS readings. Our case reports a less frequently reported interference in BIS values by ECG, which resulted into lower BIS values.

Keywords: Bispectral index, electrocardiogram, interference, low bispectral index value, sedation

How to cite this article:
Pahade A, Mowar A, Singh V, Kharayat U. Intraoperative electrocardiogram monitoring induced bispectral index interference – A misleading heart–mind connection. J Ind Coll Anesth 2022;1:77-9

How to cite this URL:
Pahade A, Mowar A, Singh V, Kharayat U. Intraoperative electrocardiogram monitoring induced bispectral index interference – A misleading heart–mind connection. J Ind Coll Anesth [serial online] 2022 [cited 2023 Oct 1];1:77-9. Available from: https://www.jicajournal.in//text.asp?2022/1/2/77/362611

  Introduction Top

Bispectral index (BIS), Aspect medical system, Newton, MA, USA) is a common but important tool in anesthesiologists' armamentariums across the world, which helps to assess the level of sedation and the effect of hypnotic drugs. A value between 40 and 60 in BIS is considered the optimal level of sedation during general anesthesia.[1] Numerous factors may affect the accuracy of BIS monitoring which may have significant implications on the appropriate dosage of hypnotic drugs.[2],[3] Although interferences due to electrocardiogram (ECG) monitoring are usually filtered by the proprietary algorithm of BIS, rarely ECG-related artifacts may result in fallacious BIS readings.

Hereby, we report a case where persistent low BIS values, eventually prompted us to analyzing BIS tracing, which showed us an unlikely source of interference.

  Case Report Top

A 72-year-old diabetic, hypertensive, hypothyroid male having coronary artery and chronic kidney disease, weighing 60 kg suffering from rectal malignancy belonging to ASA Class III, was scheduled for low anterior resection under general endotracheal anesthesia with thoracic epidural analgesia. A geriatric patient with multiple coexisting diseases necessitated the use of intraoperative BIS monitoring to ensure adequate depth of anesthesia without compromising hemodynamic safety and a proper adequate anesthesia reversal. Anesthesia was induced using propofol 90 mg (1.5 mg/kg, titrated dose) and fentanyl 120 μg (2 μg/kg). Endotracheal intubation was facilitated by atracurium 60 mg (1 mg/kg). Subsequent intraoperative anesthesia was maintained with sevoflurane (1%) along with air–oxygen mixture (50:50) and atracurium, propofol infusion along with intravenous fentanyl bolus hourly. A single morphine bolus (3 mg) was given before the skin incision. Simultaneously, epidural bupivacaine (0.125%) was initiated as titrated bolus doses at 1.5 ml/segment, followed by maintenance through a syringe pump at 5 ml/h (0.125%). Postinduction, it was observed that the BIS values were unusually low (varying between 25 and 35) not correlating with the level of anesthesia being administered. Initially, we tried adjusting the propofol infusion dose to get the BIS values in the targeted range of 40–60, which was not successful (the maximum BIS attained was 39) [Figure 1]. During this entire exercise, the patient was hemodynamically stable and did not exhibit any features suggestive of a lighter plane of anesthesia. The signal quality index was adequate, and there was no hypothermia.
Figure 1: Monitor screen showing low BIS value along with QRS like complexes on BIS tracing

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Our search for a cause of low BIS values made us analyze the BIS tracing, which revealed a waveform corresponding to the QRS complexes of ECG tracings. We changed the BIS module to rule out an instrument malfunction. However, the pattern continued to appear with the new BIS module. To verify whether low BIS values are indeed due to ECG, we transiently disconnected the ECG electrodes only to find that BIS values showed us values in our targeted range of 45–60. We continued with the same sevoflurane and propofol settings during the entire course of surgery. Postsurgery, the patient was reversed uneventfully and denied any intraoperative recall.

  Discussion Top

Interference in EEG and BIS by a variety of sources has been documented, and detection of these artifacts can often be tricky. EEG artifacts can be classified as physiological and nonphysiological. Nonphysiological artifacts are sourced from external devices (pacing devices, endoscopic shavers, and warming blankets), and these falsely increase the BIS. Physiologic artifacts originate from cardiac, glossokinetic, ocular, respiratory, and pulse artifacts. Proprietary algorithms are designed to filter most of them.[4]

Cardiac artifacts are of two types: pulse artifacts and ECG artifacts. Pulse artifacts are harder to filter since they arise from rhythmic contraction and relaxation of the heart, are of 1.2 Hz frequency, and occur when electrodes are placed on the pulsating vessel, whereas ECG algorithms are more relatively easy to identify, found in obese, short-necked patients, and filterable by proprietary algorithms.[5]

Various physicists have developed multiple algorithms to filter out ECG artifacts. A detailed description of these algorithms is beyond the scope of this article. Hemmerling et al. described a case similar to ours where they reported BIS values constantly under the expected values. They hypothesized, instead of reading BIS tracings, the monitor interpreted ECG interferences resulting in dubious low BIS values.[6] Suzuki et al. also reported a similar occurrence; however, they had placed BIS sensors at an alternate, postauricular region putting their BIS sensor closer to ECG electrodes, resulting in abnormal BIS tracing and readings.[7]

However, contrary to findings in our case and Hemmerling et al., Myles and Cairo, Puri and Nakra reported higher-than-expected BIS readings in brain-dead patients due to ECG interference.[2],[3],[6]

In view of our experience, we believe that the anesthesiologist exercises a high index of vigilance and analyze the BIS tracings periodically since the time BIS sensors are applied, rather than adjusting hypnotic drugs on isolated BIS values and be on a constant lookout for clinical signs suggestive of a lighter plane of anesthesia. The authors believe the change in the BIS module might be of help in case of equipment malfunction, the use of alternate sites of BIS sensor placement should be avoided. Concomitant use of other modalities monitoring anesthesia depth such as entropy may also be used to reconfirm the below or higher-than-expected BIS values. It is believed that entropy as a monitor to measure the depth of anesthesia is relatively resistant to interference such as ECG. However, entropy has its own limitations, as with all monitoring modalities.

It should always be remembered that monitoring devices are just aids in clinical anesthesia. No monitoring aid is free of errors and is prone to interference from a multitude of agents, as was ECG in our case and it is not the machine which is important but the anesthesiologist interpreting the machine who should exercise eternal vigilance with an open mind.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Mathur S, Patel J, Goldstein S, Jain A. Bispectral Index. 2022 Sep 19. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022. Available from: https:// www.ncbi.nlm.nih.gov/books/NBK539809. [Last updated on 2022 Nov 15].  Back to cited text no. 1
Myles PS, Cairo S. Artifact in the bispectral index in a patient with severe ischemic brain injury. Anesth Analg 2004;98:706-7.  Back to cited text no. 2
Puri GD, Nakra D. ECG artifact and BIS in severe brain injury. Anesth Analg 2005;101:1566-7.  Back to cited text no. 3
Britton JW, Frey LC, Hopp JL, Korb P, Koubeissi MZ, Lievens WE et al. Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants [Internet]. St. Louis EK, Frey LC, editors. Chicago: American Epilepsy Society; 2016. Available from: https://www.ncbi.nlm.nih.gov/books/NBK390358/. [Last accessed on 2022 Nov 15].  Back to cited text no. 4
Jiang X, Bian GB, Tian Z. Removal of artifacts from EEG signals: A review. Sensors (Basel) 2019;19:987.  Back to cited text no. 5
Hemmerling TM, Charabati S, Bracco D. Unusual case of low bispectral index values due to electrocardiographic interferences. Br J Anaesth 2008;101:877-8.  Back to cited text no. 6
Suzuki T, Kimura SY, Shinoda T. Appearance of an electrocardiogram tracing on a bispectral index monitor with plausible BIS values. J Clin Monit Comput 2016;30:123-4.  Back to cited text no. 7


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