Bispectral index

The BIS was introduced by Aspect Medical Systems, Inc. in 1994{{cite journal | vauthors = Sigl JC, Chamoun NG | title = An introduction to bispectral analysis for the electroencephalogram | journal = Journal of Clinical Monitoring | volume = 10 | issue = 6 | pages = 392–404 | date = November 1994 | pmid = 7836975 | doi = 10.1007/bf01618421 | s2cid = 1360811 }} as a novel measure of the level of consciousness by algorithmic analysis of a patient's electroencephalogram during general anesthesia. This is used in conjunction with other physiologic monitoring such as electromyography to estimate the depth of anesthesia in order to minimize the possibility of intraoperative awareness. The US Food and Drug Administration (FDA) cleared BIS monitoring in 1996 for assessing the hypnotic effects of general anesthetics and sedatives. The FDA further stated in 2003 that "...A reduction in awareness provides a public health benefit, in that BIS technology can now provide anesthestists with a way to reduce this often debilitating, yet preventable medical error". Aspect Medical was acquired by Covidien in 2009.{{cite press release|url=https://www.businesswire.com/news/home/20091106005883/en/Covidien-Completes-Acquisition-Aspect-Medical-Systems|title=Covidien Completes Acquisition Aspect Medical Systems|website=businesswire.com}}

File:BIS Monitor-Burst Suppression.JPG activity.]]

The bispectral index is a statistically based, empirically derived complex parameter. It is a weighted sum of several electroencephalographic subparameters, including a time domain, frequency domain, and high order spectral subparameters.{{cite journal | vauthors = Kaul HL, Bharti N | title = Monitoring depth of anaesthesia | journal = Indian J Anaesth | volume = 46 | issue = 4 | pages = 323–332 | year = 2002 | url = http://medind.nic.in/iad/t02/i4/iadt02i4p323.pdf | archive-url = https://web.archive.org/web/20060416081525/http://medind.nic.in/iad/t02/i4/iadt02i4p323.pdf | url-status = dead | archive-date = 16 April 2006 | access-date = 3 August 2010 }} The BIS monitor provides a single dimensionless number, which ranges from 0 (equivalent to EEG silence) to 100. A BIS value between 40 and 60 indicates an appropriate level for general anesthesia, as recommended by the manufacturer. The BIS monitor thus gives the anesthetist an indication of how "deep" under anesthesia the patient is.{{cite journal | vauthors = Kissin I | title = Depth of anesthesia and bispectral index monitoring | journal = Anesthesia and Analgesia | volume = 90 | issue = 5 | pages = 1114–1117 | date = May 2000 | pmid = 10781463 | doi = 10.1097/00000539-200005000-00021 | s2cid = 37411987 | doi-access = free }} Additionally, BIS values less than 40 for greater than 5 minutes have been associated with increased risk of stroke (hazard ratio of 3.23), MI (1.94) and death (1.41).{{cite journal | vauthors = Leslie K, Myles PS, Forbes A, Chan MT | title = The effect of bispectral index monitoring on long-term survival in the B-aware trial | journal = Anesthesia and Analgesia | volume = 110 | issue = 3 | pages = 816–22 | date = March 2010 | pmid = 19910621 | doi = 10.1213/ANE.0b013e3181c3bfb2 | s2cid = 45833138 | doi-access = free }}

The essence of BIS is to take a complex signal (the EEG), analyse it, and process the result into a single number. Several other systems claim to be able to perform the same thing. The recent availability of cheap, fast computer processors has enabled great advances in this field. When a subject is awake, the cerebral cortex is very active, and the EEG reflects vigorous activity. When asleep or under general anesthesia, the pattern of activity changes. Overall, there is a change from higher-frequency signals to lower-frequency signals (which can be shown by Fourier analysis), and there is a tendency for signal correlation from different parts of the cortex to become more random.

As with other types of EEG analysis, the calculation algorithm that the BIS monitor uses is proprietary, although it has been successfully reverse engineered.{{cite journal | vauthors = Connor CW | title = Open Reimplementation of the BIS Algorithms for Depth of Anesthesia | journal = Anesthesia and Analgesia | volume = 135 | issue = 4 | pages = 855–864 | date = October 2022 | pmid = 35767469 | pmc = 9481655 | doi = 10.1213/ANE.0000000000006119 }}

Some of the limitations of this form of processed EEG monitoring are:

• Unreliability with certain drugs, such as ketamine, nitrous oxide and ephedrine.{{cite book | vauthors = Mathur S, Patel J, Goldstein S, Jain A | chapter = Bispectral Index | title = StatPearls [Internet] | year = 2022 | location = Treasure Island (FL) | publisher = StatPearls Publishing | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK539809/ | pmid = 30969631 }}{{cite book | vauthors = Mathews DM | date = 2013 | chapter = Chapter 44. processed eeg monitoring. | veditors = Atchabahian A, Gupta R | title = The Anesthesia Guide. | publisher = McGraw Hill | chapter-url = https://accessanesthesiology.mhmedical.com/content.aspx?bookid=572§ionid=42543628 | isbn = 978-0-07-176049-2 }} Ketamine may produce a paradoxical transient increase in BIS values as this increase is associated with deepening of the hypnotic state.{{cite journal | vauthors = Hans P, Dewandre PY, Brichant JF, Bonhomme V | title = Comparative effects of ketamine on Bispectral Index and spectral entropy of the electroencephalogram under sevoflurane anaesthesia | journal = British Journal of Anaesthesia | volume = 94 | issue = 3 | pages = 336–340 | date = March 2005 | pmid = 15591328 | doi = 10.1093/bja/aei047 | url = | doi-access = free }}
• Difficulty titrating anesthetics in patients 6 months or younger.
• Interference by other medical devices such as electrosurgical cautery or forced air warming devices.
• Unreliable in cases of hypothermia or neurological impairment.
• Events unrelated to titration of anesthetic drugs can produce rapid changes in BIS values, such as cerebral hypoperfusion, gas embolism, and hemorrhage.Dao H (2014). Awareness under general anesthesia. Freeman B.S., & Berger J.S.(Eds.), Anesthesiology Core Review: Part One Basic Exam. McGraw Hill. https://accessanesthesiology.mhmedical.com/content.aspx?bookid=974§ionid=61588541
• The BIS value may lag behind the observed clinical state by 5 to 15 seconds related to EEG processing.{{cite book | vauthors = Bowdle TA | chapter = Chapter 43 - Can We Prevent Recall during Anesthesia? | veditors = Fleisher LA | title = Evidence-Based Practice of Anesthesiology | edition = Second | publisher = W.B. Saunders | date = 2009 | pages = 291–295 | isbn = 978-1-4160-5996-7 | doi = 10.1016/B978-1-4160-5996-7.00043-2

}}

BIS monitoring is widely used in operating rooms and ICUs, as well as in emergency departments. Some of the benefits that have been attributed to it include:

• Reduced time to extubation and discharge from the operating room and PACU
• Reduced risk of postoperative nausea and vomiting
• Reduced use of propofol
• Reduced risk of awareness, although this claim is questioned by some studies.

The BIS is an electroencephalogram-derived multivariant scale that, when a drug such as propofol is used, correlates with the metabolic rate of glucose.{{cite journal | vauthors = Alkire MT | title = Quantitative EEG correlations with brain glucose metabolic rate during anesthesia in volunteers | journal = Anesthesiology | volume = 89 | issue = 2 | pages = 323–333 | date = August 1998 | pmid = 9710389 | doi = 10.1097/00000542-199808000-00007 | s2cid = 26237264 | doi-access = free }} Both loss of consciousness and awakening from anesthesia are correlated with this scale.{{cite journal | vauthors = Flaishon R, Windsor A, Sigl J, Sebel PS | title = Recovery of consciousness after thiopental or propofol. Bispectral index and isolated forearm technique | journal = Anesthesiology | volume = 86 | issue = 3 | pages = 613–619 | date = March 1997 | pmid = 9066327 | doi = 10.1097/00000542-199703000-00013 | s2cid = 22800330 }} The efficacy of BIS index monitoring is not without controversy.{{cite journal | vauthors = Rosow C, Manberg PJ | title = Bispectral index monitoring | journal = Anesthesiology Clinics of North America | volume = 19 | issue = 4 | pages = 947–66, xi | date = December 2001 | pmid = 11778388 | doi = 10.1016/s0889-8537(01)80018-3 }}

Some controlled studies have found that using the BIS reduced the incidence of memory but this was not confirmed in several very large multicenter studies on awareness.{{cite journal | vauthors = McCulloch TJ | title = Use of BIS monitoring was not associated with a reduced incidence of awareness | journal = Anesthesia and Analgesia | volume = 100 | issue = 4 | pages = 1221 | date = April 2005 | pmid = 15781568 | doi = 10.1213/01.ane.0000149022.48021.24 | doi-access = free }}{{cite journal | vauthors = Avidan MS, Zhang L, Burnside BA, Finkel KJ, Searleman AC, Selvidge JA, Saager L, Turner MS, Rao S, Bottros M, Hantler C, Jacobsohn E, Evers AS | display-authors = 6 | title = Anesthesia awareness and the bispectral index | journal = The New England Journal of Medicine | volume = 358 | issue = 11 | pages = 1097–1108 | date = March 2008 | pmid = 18337600 | doi = 10.1056/NEJMoa0707361 | doi-access = free }} A Cochrane review in 2014{{cite web|url=http://summaries.cochrane.org/CD003843/ANAESTH_monitoring-the-bispectral-index-bis-to-improve-anaesthetic-delivery-and-patient-recovery-from-anaesthesia|title=Our evidence - Cochrane|website=summaries.cochrane.org}} found that "Four studies (7761 patients) that used clinical signs as a guide to anaesthetic administration in standard practice, as the control group, demonstrated a significant reduction in the risk of awareness with BIS monitoring. Four studies (26,530 patients) compared BIS monitoring with end tidal anaesthetic gas (ETAG) monitoring as a guide to management of anaesthesia and they did not demonstrate any difference in terms of intraoperative awareness". The Sociedad de Anestesiología Reanimación y Terapéutica del Dolor de Madrid recommends monitoring of anesthetic depth in accordance with literature-based evidence. BIS, however, is not explicitly endorsed. In fact, they cite an American Society of Anesthesiologists (ASA) statement saying that the decision for cerebral function monitoring should be made on an individual basis.{{Cite web |url=http://www.sarmadrid.org/html/enl/enlacesDoc.html#docSedar |title=Enlaces |work=SAR Madrid}}

The bispectral index has not been proven to measure the level of consciousness, independently of the cause of reduced consciousness (whether this be drugs, metabolic disease, hypothermia, head trauma, hypovolemia, natural sleep and so on).{{Citation needed|date=April 2007}} Not all unconscious patients will have a low BIS value, although the general clinical state may be very different from one to the other, and the prognosis may also differ.{{Citation needed|date=April 2007}} Furthermore, not all conscious patients will have a high BIS value.{{cite journal | vauthors = Schuller PJ, Newell S, Strickland PA, Barry JJ | title = Response of bispectral index to neuromuscular block in awake volunteers | journal = British Journal of Anaesthesia | volume = 115 | issue = Suppl 1 | pages = i95–i103 | date = July 2015 | pmid = 26174308 | doi = 10.1093/bja/aev072 | citeseerx = 10.1.1.1025.8968 }}

The bispectral index is prone to artifacts. Some conscious patients who are administered neuromuscular blocking agents such as succinylcholine may have low bispectral index scores; thus, the BIS may fail to detect consciousness in such patients.{{cite journal | vauthors = Messner M, Beese U, Romstöck J, Dinkel M, Tschaikowsky K | title = The bispectral index declines during neuromuscular block in fully awake persons | journal = Anesthesia and Analgesia | volume = 97 | issue = 2 | pages = 488–491 | date = August 2003 | pmid = 12873942 | doi = 10.1213/01.ane.0000072741.78244.c0 | name-list-style = amp | s2cid = 14760876 | publication-date = August 2003 | doi-access = free }} Its numbers cannot be relied upon in all situations, including brain death, circulatory arrest or hypothermia.{{cite journal | vauthors = Myles PS, Cairo S | title = Artifact in the bispectral index in a patient with severe ischemic brain injury | journal = Anesthesia and Analgesia | volume = 98 | issue = 3 | pages = 706–7, table of contents | date = March 2004 | pmid = 14980924 | doi = 10.1213/01.ANE.0000099360.49186.6B | doi-access = free }}{{cite journal | vauthors = Zanner R, Schneider G, Kochs EF | title = Falsely increased bispectral index values caused by the use of a forced-air-warming device | journal = European Journal of Anaesthesiology | volume = 23 | issue = 7 | pages = 618–619 | date = July 2006 | pmid = 16677436 | doi = 10.1017/s0265021506210779 | doi-access = free }}{{cite journal | vauthors = Fatovich DM, Jacobs IG, Celenza A, Paech MJ | title = An observational study of bispectral index monitoring for out of hospital cardiac arrest | journal = Resuscitation | volume = 69 | issue = 2 | pages = 207–212 | date = May 2006 | pmid = 16378674 | doi = 10.1016/j.resuscitation.2005.07.022 }}{{cite journal | vauthors = Wennervirta J, Salmi T, Hynynen M, Yli-Hankala A, Koivusalo AM, Van Gils M, Pöyhiä R, Vakkuri A | display-authors = 6 | title = Entropy is more resistant to artifacts than bispectral index in brain-dead organ donors | journal = Intensive Care Medicine | volume = 33 | issue = 1 | pages = 133–136 | date = January 2007 | pmid = 17091243 | pmc = 7121908 | doi = 10.1007/s00134-006-0429-6 }} A monitor of the Autonomic Nervous System (the first commercial monitor was the ANEMON-I monitor developed by former Swiss company Medical System SA based on the patent WO1997037586{{cite web|url=http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=9737586A1&KC=A1&FT=D|title=Espacenet - Bibliographic data|website=worldwide.espacenet.com}}) may be more appropriate for purposely assessing the reaction to noxious stimuli during surgery. However, a monitor of the central nervous system may be more appropriate for monitoring consciousness. After the publication of the B-Aware TrialP. Myles, K. Leslie et al. Lancet 2004 ensuring that the BIS index was below 60 was suggested to reduce the risk of anesthesia awareness during surgery for a 'high risk' group, when using a conventional anaesthetic technique.{{cite journal | vauthors = Phillips JS, Innes AJ, Naik MS | title = Corticosteroids for supraglottitis | journal = British Journal of Anaesthesia | volume = 92 | issue = 3 | pages = 454–455 | date = March 2004 | pmid = 14970144 | doi = 10.1093/bja/aeh527 | doi-access = free }} However, this result was not reproduced by a recently published randomized control trial, the "B-Unaware Trial". In it, the use of BIS monitoring was not associated with a lower incidence of anesthesia awareness. In some cases, the BIS may underestimate the depth of anesthesia, leading the anesthetist to administer a higher than necessary dose of anesthetic agent(s). In such cases, the patient may be anesthetized to a lower BIS level than is necessary for the surgery or procedure—this is called "treating the BIS", and may result in a deeper level of anesthesia than required).{{Citation needed|date=April 2007}}

The monitoring of EEG in ICU patients has been employed in one form or other for more than two decades. BIS monitoring is also being used during transport of critically ill patients in ambulances, helicopters and other vehicles.

Some studies show a greater incidence of intra-operative awareness in children, when compared to adults.{{cite journal | vauthors = Davidson AJ, Huang GH, Czarnecki C, Gibson MA, Stewart SA, Jamsen K, Stargatt R | title = Awareness during anesthesia in children: a prospective cohort study | journal = Anesthesia and Analgesia | volume = 100 | issue = 3 | pages = 653–661 | date = March 2005 | pmid = 15728046 | doi = 10.1213/01.ANE.0000150604.73481.00 | s2cid = 22488115 | doi-access = free }} The correlation between bispectral index in children over one year and state of consciousness has already been proven, although in younger patients the monitor is unreliable because of the differences between immature infant EEG patterns and the adult EEG patterns that the BIS algorithm utilises.{{cite journal | vauthors = McKeever S, Johnston L, Davidson AJ | title = An observational study exploring amplitude-integrated electroencephalogram and spectral edge frequency during paediatric anaesthesia | journal = Anaesthesia and Intensive Care | volume = 40 | issue = 2 | pages = 275–284 | date = March 2012 | pmid = 22417022 | doi = 10.1177/0310057X1204000210 | doi-access = free }}{{cite journal | vauthors = McKeever S, Johnston L, Davidson AJ | title = Sevoflurane-induced changes in infants' quantifiable electroencephalogram parameters | journal = Pediatric Anesthesia | volume = 24 | issue = 7 | pages = 766–773 | date = July 2014 | pmid = 24612073 | doi = 10.1111/pan.12366 | s2cid = 206243289 | url = http://researchopen.lsbu.ac.uk/461/6/Sevoflurane-induced_changes_in_infants_quantifiable_electroencephalogram_parameters.pdf }}

Specifically for intraoperative awareness, according to a 2013 article in The Atlantic, "Today, the BIS monitor has become the most controversial medical device in anesthesiology, if not all of surgery."{{cite web |url= https://www.theatlantic.com/magazine/archive/2013/01/awakening/309188/ |title=Awakening| vauthors = Lang L |work=The Atlantic|date=2013}}

• Anaesthetic machine
• Entropy monitoring
• Evoked potentials
• Respiratory monitoring
• Spectral edge frequency

{{reflist}}

• {{cite journal|vauthors=Grover VK, Bharti N|title=Measuring depth of anaesthesia - an overview on the currently available monitoring systems|journal=The Indian Anaesthetists' Forum|volume=1|issue=1|pages=1–33|year=2008|issn=0973-0311|url=http://www.theiaforum.org/Article_Folder/measuring-depth-of-anaesthesia-available-monitoring-systems.pdf|access-date=2011-01-02|url-status=dead|archive-url=https://web.archive.org/web/20101128180221/http://theiaforum.org/Article_Folder/measuring-depth-of-anaesthesia-available-monitoring-systems.pdf|archive-date=2010-11-28}}

(Commercial interest publications)

• [https://web.archive.org/web/20191204173217/https://www.anandic.com/en/training-center/bis-education BIS Education] BIS Education

{{DEFAULTSORT:Bispectral Index}}

Category:Anesthesia

Category:Anesthetic equipment