Engineering:Bispectral index

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BIS monitor

Bispectral index (BIS) is one of several technologies used to monitor depth of anesthesia. BIS monitors are used to supplement Guedel's classification system for determining depth of anesthesia. Titrating anesthetic agents to a specific bispectral index during general anesthesia in adults (and children over 1 year old) allows the anesthetist to adjust the amount of anesthetic agent to the needs of the patient, possibly resulting in a more rapid emergence from anesthesia. Use of the BIS monitor could reduce the incidence of intraoperative awareness during anaesthesia.[1] The exact details of the algorithm used to create the BIS index have not been disclosed by the company that developed it.

BIS cannot be used as the sole monitor of anaesthesia, as it is affected by several other factors, including the anaesthetic drugs used (BIS is relatively insensitive to agents such as ketamine and nitrous oxide), and muscle movement or artefact from surgical equipment. BIS is used as an adjunct to monitoring under anaesthesia - its use has been shown to reduce overall dose of anaesthetic agent used and therefore may improve recovery time from anaesthesia.[2]

History

The BIS was introduced by Aspect Medical Systems, Inc. in 1994[3] 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.[4]

Calculation

Bispectral index monitor indicating a nearly isoelectric pattern of electroencephalographic 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.[5] 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.[6] 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).[7]

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.[8]

Limitations

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

  • Unreliability with certain drugs, such as ketamine, nitrous oxide and ephedrine.[9][10] Ketamine may produce a paradoxical transient increase in BIS values as this increase is associated with deepening of the hypnotic state.[11]
  • Difficulty titrating anesthetics in patients 6 months or younger.[9]
  • Interference by other medical devices such as electrosurgical cautery.[9]
  • Unreliable in cases of hypothermia or neurological impairment.[9]
  • Events unrelated to titration of anesthetic drugs can produce rapid changes in BIS values, such as cerebral hypoperfusion, gas embolism, and hemorrhage.[12]
  • The BIS value may lag behind the observed clinical state by 5 to 15 seconds related to EEG processing.[13]

Benefits

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:[9]

  • Reduced time to extubation and discharge from the operating room and PACU
  • Reduced risk of postoperative nausea and vomiting
  • Reducing the use of propofol
  • Reduced risk of awareness, unless this claim is questioned by some studies.[14]

Relevance

The BIS is an electroencephalogram-derived multivariant scale that, when a drug such a propofol is used, correlates with the metabolic rate of glucose.[15] Both loss of consciousness and awakening from anesthesia are correlated with this scale.[16] The efficacy of BIS index monitoring is not without controversy.[17]

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.[14][18] A Cochrane review in 2014[19] 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.[20]

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] 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] Furthermore, not all conscious patients will have a high BIS value.[21]

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.[22] Its numbers cannot be relied upon in all situations, including brain death, circulatory arrest or hypothermia.[23][24][25][26] 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[27]) 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 Trial[28] 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.[29] However, this result was not reproduced by a recently published randomized control trial, the "B-Unaware Trial".[18] 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]

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.[30] 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.[31][32]

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."[33]

See also

References

  1. ↑ "Depth of anaesthesia monitors – Bispectral Index (BIS), E-Entropy and Narcotrend-Compact M - Guidance and guidelines - NICE". 21 November 2012. http://www.nice.org.uk/guidance/dg6. 
  2. ↑ "Bispectral index for improving intraoperative awareness and early postoperative recovery in adults". The Cochrane Database of Systematic Reviews 9 (9): CD003843. September 2019. doi:10.1002/14651858.CD003843.pub4. PMID 31557307. 
  3. ↑ "An introduction to bispectral analysis for the electroencephalogram". Journal of Clinical Monitoring 10 (6): 392–404. November 1994. doi:10.1007/bf01618421. PMID 7836975. 
  4. ↑ "Covidien Completes Acquisition Aspect Medical Systems". businesswire.com (Press release).
  5. ↑ "Monitoring depth of anaesthesia". Indian J Anaesth 46 (4): 323–332. 2002. http://medind.nic.in/iad/t02/i4/iadt02i4p323.pdf. Retrieved 3 August 2010. 
  6. ↑ "Depth of anesthesia and bispectral index monitoring". Anesthesia and Analgesia 90 (5): 1114–1117. May 2000. doi:10.1097/00000539-200005000-00021. PMID 10781463. 
  7. ↑ "The effect of bispectral index monitoring on long-term survival in the B-aware trial". Anesthesia and Analgesia 110 (3): 816–22. March 2010. doi:10.1213/ANE.0b013e3181c3bfb2. PMID 19910621. 
  8. ↑ "Open Reimplementation of the BIS Algorithms for Depth of Anesthesia". Anesthesia and Analgesia 135 (4): 855–864. October 2022. doi:10.1213/ANE.0000000000006119. PMID 35767469. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 "Bispectral Index". StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. 2022. https://www.ncbi.nlm.nih.gov/books/NBK539809/. 
  10. ↑ "Chapter 44. processed eeg monitoring.". The Anesthesia Guide.. McGraw Hill. 2013. ISBN 978-0-07-176049-2. https://accessanesthesiology.mhmedical.com/content.aspx?bookid=572&sectionid=42543628. 
  11. ↑ "Comparative effects of ketamine on Bispectral Index and spectral entropy of the electroencephalogram under sevoflurane anaesthesia". British Journal of Anaesthesia 94 (3): 336–340. March 2005. doi:10.1093/bja/aei047. PMID 15591328. 
  12. ↑ 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&sectionid=61588541
  13. ↑ "Chapter 43 - Can We Prevent Recall during Anesthesia?". Evidence-Based Practice of Anesthesiology (Second ed.). W.B. Saunders. 2009. pp. 291–295. doi:10.1016/B978-1-4160-5996-7.00043-2. ISBN 978-1-4160-5996-7. 
  14. ↑ 14.0 14.1 "Use of BIS monitoring was not associated with a reduced incidence of awareness". Anesthesia and Analgesia 100 (4): 1221. April 2005. doi:10.1213/01.ane.0000149022.48021.24. PMID 15781568. 
  15. ↑ "Quantitative EEG correlations with brain glucose metabolic rate during anesthesia in volunteers". Anesthesiology 89 (2): 323–333. August 1998. doi:10.1097/00000542-199808000-00007. PMID 9710389. 
  16. ↑ "Recovery of consciousness after thiopental or propofol. Bispectral index and isolated forearm technique". Anesthesiology 86 (3): 613–619. March 1997. doi:10.1097/00000542-199703000-00013. PMID 9066327. 
  17. ↑ "Bispectral index monitoring". Anesthesiology Clinics of North America 19 (4): 947–66, xi. December 2001. doi:10.1016/s0889-8537(01)80018-3. PMID 11778388. 
  18. ↑ 18.0 18.1 "Anesthesia awareness and the bispectral index". The New England Journal of Medicine 358 (11): 1097–1108. March 2008. doi:10.1056/NEJMoa0707361. PMID 18337600. 
  19. ↑ "Our evidence - Cochrane". http://summaries.cochrane.org/CD003843/ANAESTH_monitoring-the-bispectral-index-bis-to-improve-anaesthetic-delivery-and-patient-recovery-from-anaesthesia. 
  20. ↑ "Enlaces". SAR Madrid. http://www.sarmadrid.org/html/enl/enlacesDoc.html#docSedar. 
  21. ↑ "Response of bispectral index to neuromuscular block in awake volunteers". British Journal of Anaesthesia 115 (Suppl 1): i95–i103. July 2015. doi:10.1093/bja/aev072. PMID 26174308. 
  22. ↑ "The bispectral index declines during neuromuscular block in fully awake persons". Anesthesia and Analgesia 97 (2): 488–491. August 2003. doi:10.1213/01.ane.0000072741.78244.c0. PMID 12873942. 
  23. ↑ "Artifact in the bispectral index in a patient with severe ischemic brain injury". Anesthesia and Analgesia 98 (3): 706–7, table of contents. March 2004. doi:10.1213/01.ANE.0000099360.49186.6B. PMID 14980924. 
  24. ↑ "Falsely increased bispectral index values caused by the use of a forced-air-warming device". European Journal of Anaesthesiology 23 (7): 618–619. July 2006. doi:10.1017/s0265021506210779. PMID 16677436. 
  25. ↑ "An observational study of bispectral index monitoring for out of hospital cardiac arrest". Resuscitation 69 (2): 207–212. May 2006. doi:10.1016/j.resuscitation.2005.07.022. PMID 16378674. 
  26. ↑ "Entropy is more resistant to artifacts than bispectral index in brain-dead organ donors". Intensive Care Medicine 33 (1): 133–136. January 2007. doi:10.1007/s00134-006-0429-6. PMID 17091243. 
  27. ↑ "Espacenet - Bibliographic data". http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=9737586A1&KC=A1&FT=D. 
  28. ↑ P. Myles, K. Leslie et al. Lancet 2004
  29. ↑ "Corticosteroids for supraglottitis". British Journal of Anaesthesia 92 (3): 454–455. March 2004. doi:10.1093/bja/aeh527. PMID 14970144. 
  30. ↑ "Awareness during anesthesia in children: a prospective cohort study". Anesthesia and Analgesia 100 (3): 653–661. March 2005. doi:10.1213/01.ANE.0000150604.73481.00. PMID 15728046. 
  31. ↑ "An observational study exploring amplitude-integrated electroencephalogram and spectral edge frequency during paediatric anaesthesia". Anaesthesia and Intensive Care 40 (2): 275–284. March 2012. doi:10.1177/0310057X1204000210. PMID 22417022. 
  32. ↑ "Sevoflurane-induced changes in infants' quantifiable electroencephalogram parameters". Pediatric Anesthesia 24 (7): 766–773. July 2014. doi:10.1111/pan.12366. PMID 24612073. http://researchopen.lsbu.ac.uk/461/6/Sevoflurane-induced_changes_in_infants_quantifiable_electroencephalogram_parameters.pdf. 
  33. ↑ "Awakening". The Atlantic. 2013. https://www.theatlantic.com/magazine/archive/2013/01/awakening/309188/. 

Further reading

External links

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