Bispectral Index (BIS) Monitoring


  • BIS monitor was developed by Aspect Medical Systems
  • BIS = bispectral index
  • other ‘depth of anaesthesia’ monitors exist (e.g. Entropy)


  • used to monitor the depth of sedation or anaesthesia


  • Sensor – consists of disposable, wet gel electrodes
  • Cable
  • Monitoring module – interfaces with anaesthesia machine or monitoring systems


  •  best describe as a monitor of the depth of the hypnotic component of anaesthesia
  • frontoparietal application of electrodes
  • the monitor generates a number
    — 100 = normal cortical activity (maximum alertness)
    — 0 = cortical electrical silence
  • an EMG signal and Signal Quality Index is displayed as well as a single channel EEG

The BIS algorithm

  • EEG data recorded from healthy adults who underwent repeated transitions between consciousness and unconsciousness using different anaesthetic regimens
  • analysis identified those features of EEG recordings that best correlated with clinical depth of sedation/anaesthesia – in essence, the complexity of the EEG reduces with increasing depth of anaesthesia
  • these were fitted to a model by multivariate logistic regression
  • the resulting algorithm generates a bispectral index (BIS)
  • it has been validated on healthy and now other patient populations



  • BIS < 60 results in very low levels of post-op recall
  • shown to lower anaesthetic consumption
  • slightly quicker awaking
  • safe with diathermy and defibrillation


  • opioids produce changes in depth of consciousness not discernible by BIS
  • BIS is not able to predict movement in response to surgical stimulation
  • BIS values display incredible variability
  • not helpful when using N2O or ketamine
  • cannot use in children under 5


  • low BIS associated with increasing delirium -> this can increase morbidity and mortality
  • currently no high level evidence to guide use in ICU
  • possible role for patients who are paralysed in the titration of adequate amounts of sedation and analgesia
  • may have an emerging role in out-of-hospital cardiac arrest

CCC Neurocritical Care Series

Journal articles

  • Ball J. How useful is the bispectral index in the management of ICU patients? Minerva Anestesiol. 2002 Apr;68(4):248-51. PMID: 12024092.
  • Bennett C, Voss LJ, Barnard JP, Sleigh JW. Practical use of the raw electroencephalogram waveform during general anesthesia: the art and science.Anesth Analg. 2009 Aug;109(2):539-50. PMID: 19608830
  • Bigham C, Bigham S, Jones C. Does the bispectral index monitor have a role in intensive care? JICS 2012 Oct;13(4):314-319

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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