Bispectral Index™ monitoring

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Bispectral Index™ monitoring

The Bispectral Index (BIS™) monitor is primarily used to measure anesthetic depth for general anesthesia.1–4 Anesthesia that is too light can lead to intraoperative awareness with recall, whereas anesthesia that is too deep is associated with adverse short-term outcomes like delayed emergence, and adverse long-term outcomes postoperative cognitive dysfunction at 12 weeks.5,6

In this MedEd Bytes series, we learn about the application of BIS™ monitoring to ensure adequate depth of anesthesia for a patient under general anesthesia.

Byte 1: When to use BIS™ monitoring

The BIS™ monitor allows practitioners to safely titrate the delivery of total IV anesthesia or volatile-based general anesthesia to the appropriate depth for the patient.5,7

Video: MedEd Bytes BIS™ 01 - (02:11)

Byte 2: The BIS™ index range

The BIS™ index is a unitless measure of brain activity that is calculated by an algorithm. This algorithm was developed through the interpretation of a vast quantity of empirical data of patients under general anesthesia.

Video: MedEd Bytes BIS™ 02 - (02:24)

Byte 3: BIS™ monitoring system benefits: awareness/recall prevention

The BIS™ monitor was designed to monitor brain activity with the specific goal of identifying the depth of anesthesia that will prevent intraoperative awareness and recall.

Video: MedEd Bytes BIS™ 03 - (02:02)

Byte 4: BIS™ monitoring system benefits: PONV reduction

The use of propofol instead of inhalational anesthetics can reduce PONV and using EEG monitoring such as BIS™ monitoring provides the ability to consistently monitor anesthetic depth while doing so.7,8

Video: MedEd Bytes BIS™ 04 - (02:22)

Byte 5: BIS™ monitoring system benefits: avoiding overdose

Using a BIS™ monitor not only helps guide practitioners to avoid underdosing anesthesia, but also to avoid overdosing and its associated adverse outcomes.6,9,10,11

Video: MedEd Bytes BIS™ 05 - (02:00)

Byte 6: BIS™ monitoring use in resident and fellow training

The American Society for Enhanced Recovery and Perioperative Quality Initiative’s consensus statement provides a strong recommendation that clinicians be knowledgeable in electroencephalography, or EEG interpretation.12

Video: MedEd Bytes BIS™ 06 - (01:54)

Byte 7: Intravenous anesthesia and greenhouse gasses

Because of the contribution that volatile agents make to the greenhouse gas effect, it has been hypothesized that the use of TIVA would reduce the environmental impact of anesthesia.13

Video: MedEd Bytes BIS™ 07 - (02:08)

Byte 8: How BIS™ monitoring helps achieve anesthetic goals

The BIS™ monitor provides a straightforward index which measures the actual clinical effects that anesthetic agents exert on a patient’s consciousness.

Video: MedEd Bytes BIS™ 08 - (02:11)

Byte 9: Why measure anesthetic effect with the BIS™ monitor?

The use of a BIS™ monitor has been demonstrated to reduce the incidence of intraoperative awareness with recall.5

Video: MedEd Bytes BIS™ 09 - (02:27)

Byte 10: ERAS society guidelines: strong recommendation for depth of anesthesia monitoring

The American Society of Enhanced Recovery strongly recommends monitoring processed EEG, like what BIS™ monitor provides, during surgery whenever TIVA is used in order to reduce the risk of intraoperative awareness with recall.12

Video: MedEd Bytes BIS™ 10 - (02:06)

Byte 11: BIS™ monitoring in elderly patients

The BIS™ monitor allows practitioners to safely titrate the delivery of total IV anesthesia or volatile-based general anesthesia to the appropriate depth for the patient.5,7

Video: MedEd Bytes BIS™ 11 - (02:21)

Byte 12: Breakdown of an EEG waveform

Decades of empirical research have revealed that specific patterns on EEG correspond with specific states of the brain.

Video: MedEd Bytes BIS™ 12 - (02:14)

Byte 13: EEG waveform interpretation

With enough practice, anesthesia providers can identify which EEG waveforms are associated with high and lower levels of consciousness.

Video: MedEd Bytes BIS™ 13 - (02:15)

Byte 14: DSA overview

An arguably easier way to assess EEG activity over time is by reading a special type of display called a density spectral array.

Video: MedEd Bytes BIS™ 14 - (02:16)

Byte 15: DSA drug signatures

The administration of specific anesthetic agents is associated with very specific patterns that emerge on a density spectral array.

Video: MedEd Bytes BIS™ 15 - (02:17)

The BIS™ monitoring system should not be used as the sole basis for diagnosis or therapy and is intended only as an adjunct in patient assessment. Reliance on the BIS™ monitoring system alone for intraoperative anesthetic management is not recommended.


Alkire MT. Quantitative EEG correlations with brain glucose metabolic rate during anesthesia in volunteers. Anesthesiology. 1998;89(2):323–333.


Flaishon R, Windsor A, Sigl J, Sebel PS. Recovery of consciousness after thiopental or propofol. Bispectral index and isolated forearm technique. Anesthesiology. 1997;86(3):613–619.


Glass PS, Bloom M, Kearse L, Rosow C, Sebel P, Manberg P. Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. Anesthesiology. 1997;86(4):836–847


Leslie K, Sessler DI, Schroeder M, Walters K. Propofol blood concentration and the Bispectral Index predict suppression of learning during propofol/epidural anesthesia in volunteers. Anesth Analg. 1995;81(6):1269–1274.


Lewis SR, Pritchard MW, Fawcett LJ, Punjasawadwong Y. Bispectral index for improving intraoperative awareness and early postoperative recovery in adults. Cochrane Database Syst Rev. 2019;9(9):CD003843. doi:10.1002/14651858.CD003843.pub4


Bocskai T, Kovács M, Szakács Z, et al. Is the bispectral index monitoring protective against postoperative cognitive decline? A systematic review with meta-analysis. PLoS One. 2020;15(2):e0229018.


Zhang C, Xu L, Ma YQ, et al. Bispectral index monitoring prevent awareness during total intravenous anesthesia: a prospective, randomized, double-blinded, multi-center controlled trial. Chin Med J (Engl). 2011 Nov;124(22):3664–3669.


Apfel CC, Korttila K, Abdalla M, et al. A factorial trial of six interventions for the prevention of postoperative nausea and vomiting. N Engl J Med. 2004;350(24):2441–2451.


Pawar N, Barreto Chang OL. Burst suppression during general anesthesia and postoperative outcomes: mini review. Front Syst Neurosci. 2022;15:767489.


Evered LA, Chan MTV, Han R, et al. Anaesthetic depth and delirium after major surgery: a randomised clinical trial. Br J Anaesth. 2021;127(5):704–712.


Punjasawadwong Y, Chau-In W, Laopaiboon M, Punjasawadwong S, Pin-On P. Processed electroencephalogram and evoked potential techniques for amelioration of postoperative delirium and cognitive dysfunction following non-cardiac and non-neurosurgical procedures in adults. Cochrane Database Syst Rev. 2018;5(5):CD011283.


American Society for Enhanced Recovery and Perioperative Quality Initiative joint consensus statement on the role of neuromonitoring in perioperative outcomes: electroencephalography. Anesth Analg. 2020;130(5):1278–1291.   


McGain F, Muret J, Lawson C, Sherman JD. Environmental sustainability in anaesthesia and critical care. Br J Anaesth. 2020;125(5):680–692.