Bispectral Index (BIS) Monitoring

OVERVIEW

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

USES

• used to monitor the depth of sedation or anaesthesia

DESCRIPTION

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

METHOD OF USE

•  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

COMPLICATIONS

Benefits

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

Problems

• 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

EVIDENCE IN ICU

• 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

References and Links

LITFL

• CCC — Electroencephalogram
• CCC — Continuous EEG Monitoring
• CCC — BIS Monitoring

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