From the Guidelines
For intraoperative anesthesia, the recommended target range for processed EEG monitoring, such as Bispectral Index (BIS) or similar indices, is typically between 40-60, as this range is associated with a low risk of awareness and optimal anesthesia depth. This recommendation is based on the most recent guidelines from the Association of Anaesthetists, which suggest that processed EEG monitoring can aid in adjusting the dose of anesthetic drug and reduce the incidence of adverse effects, including accidental awareness during general anesthesia (AAGA) 1. The use of processed EEG monitoring, such as BIS, has been shown to reduce the risk of AAGA, improve early recovery times, and reduce the incidence of postoperative delirium and postoperative cognitive dysfunction 1.
When using processed EEG monitoring, it is essential to develop a basic understanding of EEG waveforms and the interpretation of information from power spectral analysis, rather than relying solely on index values displayed by the monitors 1. The monitoring should start before induction and continue at least until full recovery from the effects of the neuromuscular blockade drug has been confirmed 1.
Key considerations for processed EEG monitoring include:
- Starting monitoring before induction of anesthesia
- Continuing monitoring until full recovery from neuromuscular blockade
- Adjusting anesthetic dose based on individual patient factors, such as age and comorbidities
- Using processed EEG monitoring as part of a comprehensive approach to anesthesia monitoring, including clinical signs and hemodynamic parameters 1.
By following these guidelines and using processed EEG monitoring effectively, anesthetists can optimize anesthesia depth and reduce the risk of adverse effects, ultimately improving patient outcomes and quality of life.
From the Research
Targets for Depth of Anaesthesia Monitoring
The targets for depth of anaesthesia monitoring are not strictly defined, but several studies provide guidance on the recommended ranges.
- A study published in 2019 2 found that BIS target values differed between studies, but all were within a range of values between 40 to 60.
- Another study from 2001 3 observed that the BIS scores of responders to voice were significantly different from nonresponders, with a mean BIS score of 86 +/- 10 for responders and 74 +/- 14 for nonresponders.
- A 2011 study 4 noted that deep anesthesia (BIS < 45) during the intraoperative period is associated with increased postoperative mortality.
Factors Affecting Depth of Anaesthesia Monitoring
Several factors can affect the accuracy of depth of anaesthesia monitoring, including:
- The use of neuromuscular blocking agents, which can affect the readings of brain function monitors 5
- The type of anaesthetic agent used, which can influence the relationship between BIS scores and sedation depth 3
- Inter-individual variability in BIS scores, which can make it difficult to predict sedation depth 6, 3
Recommendations for Practice
Based on the available evidence, it is recommended that: