Asleep or awake? That is the question… A review of techniques available for monitoring the depth of anaesthesia
More details
Hide details
Department of Anaesthesiology and Intensive Care, School of Medicine, Collegium Medicum, University of Warmia and Mazury in Olsztyn, Poland
Department of Nursing, School of Public Health, Collegium Medicum, University of Warmia and Mazury in Olsztyn, Poland
Submission date: 2019-08-19
Final revision date: 2020-01-22
Acceptance date: 2020-03-14
Online publication date: 2020-04-14
Corresponding author
Lidia Glinka   

Department of Anaesthesiology and Intensive Care, School of Medicine, Collegium Medicum, University of Warmia and Mazury, Warszawska 30, 10-082 Olsztyn, Poland. Phone:+4889 524 53 08.
Pol. Ann. Med. 2020;27(2):214-219
The problem of intraoperative awareness concerns about 0.1%–0.2% of patients .The perfect method to evaluate the depth of sleep should be objective, so that the response is quick and precise – to increase or decrease the depth of anaesthesia. More scales originated in order to detect cases of intraoperative awareness. Also, new equipment was built so that anaesthesiologists could properly monitor the depth of anaesthesia.

The aim is to describe methods and devices monitoring the depth of anaesthesia.

Material and methods:
This work was based on the available literature and the experience of the authors.

Results and discussion:
Recently a few devices were constructed, all of which can be divided into passive and active systems. Passive systems assess the collected data, while active ones first stimulate and then receive and process data. Passive systems use computer analysis of electroencephalographic signal, and some of them additionally evaluate alterations of frontal electromyogram. According to some, monitors currently available on the market show around 80% effectiveness in preventing intraoperative awareness. Other researchers showed that evidence of their effect on intraoperative awareness is limited.

It seems that when it comes to the effect of anaesthetic agents on such a precise organ as the brain, there is still much to discover. As long as we do not fully know what awareness is and what mechanisms influence the state of staying awake and of anaesthetic sleep, and on which levels it happens, we will not be able to prevent intraoperative awareness effectively.

None declared.
None declared.
Rondio Z. [Anesthesiology in Poland – 50th anniversary of the specialty]. Anest Intens Ter. 2002;4:235–236 [in Polish].
Plomley F. Operations upon the Eye. To the Editor of The Lancet. Lancet. 1847;1:134–135. In: The History of Anesthesiology. Reprint Series: Part 4. Signs And Stages of Anesthesia. 1974. https://www.woodlibrarymuseum..... Accessed February 1, 2019.
Snow J. On the Inhalation of Vapors of Ether in Surgical Operations: Containing a Description of the Various Stages of Etherization, and a Statement of the Result of Nearly Eighty Operations in which Ether has been Employed in St. George’s and University College Hospitals. London: John Churchill; 1847.
Guedel AE. Inhalational anesthesia. A fundamental quide. New York: Macmillan; 1937.
Ghoneim M. Etiology and risk factor of intraoperative awereness. In: Mashour GA, ed. Consciousness, Awareness and Anesthesia. New York: Cambridge University Press; 2010.
Woodbridge P. Changing concepts concerning depth of anesthesia. Anesthesiology. 1957;18(4):536–550.
Prys-Roberts C. Anesthesia: a practical or impractical construct? Br J Anaesth. 1987;59(11):1341–1345.
Shafer SL, Stanski DR. Defining depth of anesthesia. Handb Exp Pharmacol. 2008;182:409–423.
Ziętkiewicz M, Nestorowicz A. Intraoperative awareness – recommendations of the Committee on Quality and Safety in Anaesthesia. Polish Society of Anaesthesiology and Intensive Therapy. Anaesthesiol Intensive Ther. 2012;44(2):57–62.
Myles PS, Williams D, Hendrata M, Anderson H, Weeks A. Patient satisfaction after anaesthesia and surgery: Results of a prospective survey of 10,811 patients. Br J Anaesth. 2000;84(1):6–10.
Nordström O, Engström AM, Persson S, Sandin R. Incidence of awareness in total i.v. anaesthesia based on propofol, alfentanil and neuromuscular blockade. Acta Anaesthesiol Scand. 1997;41(8):978–984.
Sandin RH, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: A prospective case study. Lancet. 2000;355(9205):707–11.
Sebel PS, Bowdle TA, Ghoneim MM, et al. The incidence of awareness during anesthesia: A multicenter United States study. Anesth Analg. 2004;99:833–839.
Leslie K, Myles PS, Forbes A, Chan MT, Short TG, Swallow SK. Recovery from bispectral index - guided anaesthesia in a large randomized controlled trial of patients at high risk of awareness. Anaesth Inten Care. 2005;33:443–451.
O’Connor MF, Daves SM, Tung A, Cook RI, Thisted R, Apfelbaum J. BIS monitoring to prevent awareness during general anesthesia. Anesthesiology. 2001;94(3):520–522.
Godard N, Smith D. Unintended awareness and monitoring of depth of anaesthesia. Contin Educ Anaesth Crit Care Pain Crit Care Pain. 2013;13(6):213–217.
Wu CC, Mok MS, Lin CS, Han SR. EEG-bispectral index changes with ketamine versus thiamylal induction of anesthesia. Acta Aneasthesiol Sin. 2001;39(1):11–15.
Sleigh JW, Barnard JPM. Entropy is blind to nitrous oxide. Can we see why? Br J Anaesth. 2004;92(2):159–161.
Laitio RM, Kaskinoro K, Särkelä MO, et al. Bispectral index, entropy, and quantitative electroencephalogram during single xenon anesthesia. Anesthesiology. 2008;108(1):63–70.
Kowalczyk M. Perioperative monitoring of central nervous system’s functions. Anest Ratow. 2017;11:336–334 [in Polish].
Weber F, Walhout LC, Escher JC. The impact of Narcotrend™ EEG-guided propofol administration on the speed of recovery from pediatric procedural sedation-A randomized controlled trial. Paediatr Anaesth. 2018;28(5):443–449.
Machała W, Śmiechowicz K, Patyk M, Lesiak P. Multimodal brain monitoring during anaesthesia. A review. Anestezjol Intens Ter. 2005;4:268–273 [in Polish].
Rudner R, Jałowiecki P, Kawecki P. Modern electroencephalography and anaesthesiology. Anestezjol Int Ter. 2001;4:253–260 [in Polish].
American Society of Anesthesiologists Task Force on Intraoperative Awareness. Practice advisory for intraoperative awareness and brain function monitoring. A Report by the American Society of Anesthesiologists Task Force on Intraoperative Awareness. Anesthesiology. 2006;104(4):847–864.
Singh S, Bansal S, Kumar G, Gupta I, Thakur JR. Entropy as an indicator to measure depth of anaesthesia for laryngeal mask airway (LMA) insertion during sevoflurane and propofol anaesthesia. J Clin Diagn Res. 2017;11(7):UC01–UC03.
Mathews D, Christenson C, Farhang B, Mathews J. Comparison of the qCON and Sedline depth of anesthesia monitors to predict the hypnotic effect during desflurane general anesthesia. Accessed: February 1, 2019.
Li TN, Li Y. Depth of anaesthesia monitors and latest algorithms. Asian Pac J Trop Med. 2014;7(6):429–437.
Solari D, Miroz JP, Oddo M. Opening a window to the injured brain: non-invasive neuromonitoring with quantitative pupillometry. In: Vincent JL, ed. Annual Update in Intensive Care and Emergency Medicine 2018. Cham: Springer. 2018:503–509.
Ekman A, Lindholm ML, Lennmarken C, Sandin R. Reduction in the incidence of awareness using BIS monitoring. Acta Anaesthesiol Scand. 2004;48(1):20–26.
Punjasawadwong Y, Phongchiewboon A, Bunchungmongkol N. Bispectral index for improving anaesthetic delivery and postoperative recovery. Cochrane Database Syst Rev. 2007;4:CD003843.
Punjasawadwong Y, Phongchiewboon A, Bunchungmongkol N. Bispectral index for improving anaesthetic delivery and postoperative recovery. Cochrane Database Syst Rev. 2014;6:CDOO3843. 1858.CDOO3843.pub3.
Shetty RM, Bellini A, Wijayatilake DS. et al. BIS monitoring versus clinical assessment for sedation in mechanically ventilated adults in the intensive care unit and its impact on clinical outcomes and resource utilization. Cochrane Database Syst Rev. 2018;21(2):CDO11240.
Shepherd J, Jones J, Frampton G, Bryant J, et al. Clinical effectiveness and cost-effectiveness of depth anaesthesia monitoring(E-Entropy, Bispectral index and Narcotrend);a systematic review and economic evaluation. Health Technol Assess. 2013;17(34):1–264.
Journals System - logo
Scroll to top