What BIS (Bispectral Index) values are recommended for general anesthesia?

BIS Values for General Anesthesia

BIS values of 40 to 60 have been recommended for general anesthesia to ensure adequate depth of anesthesia while minimizing the risk of awareness. 1

Understanding BIS Monitoring

• BIS monitoring is a noninvasive method that uses electroencephalographic (EEG) waveforms to assess a patient's level of consciousness during anesthesia 1
• The BIS monitor analyzes EEG signals using complex algorithms to generate a BIS index ranging from 0 to 100 1
• Higher BIS values indicate greater consciousness: 100 represents fully awake, while 0 represents complete EEG suppression 1

BIS Value Ranges and Clinical Correlations

• BIS values between 40 and 59 correspond to general anesthesia 1
• BIS values between 60 and 69 indicate deep sedation 1
• BIS values between 70 and 90 represent moderate sedation 1
• BIS values below 40 denote deep hypnosis 1

Evidence Supporting BIS Monitoring in General Anesthesia

• BIS monitoring has been shown to reduce the incidence of intraoperative awareness during general anesthesia when maintained between 40-60 2, 3
• In a large multicenter controlled trial, BIS-guided anesthesia (target 40-60) reduced confirmed awareness cases to 0.14% compared to 0.65% in the control group 2
• For elderly patients (>60 years), targeting a lighter level of anesthesia with a BIS of approximately 50 can significantly reduce postoperative delirium 4, 5

Clinical Applications and Limitations

• BIS monitoring is particularly valuable during total intravenous anesthesia (TIVA) with neuromuscular blocking drugs 6
• The American Society of Anesthesiologists recommends processed EEG monitoring such as BIS for patients at higher risk of awareness 4
• BIS values may be affected by certain anesthetic agents differently - ketamine and sevoflurane may paradoxically increase BIS values despite adequate anesthesia depth 1
• BIS monitoring may not reliably predict awareness reactions to intubation in some patients, even when values are maintained between 50-60 7

Practical Implementation

• For most surgical procedures under general anesthesia, maintain BIS values between 40-60 1
• During induction and intubation, be aware that BIS values may lag behind actual consciousness changes 7
• During maintenance phase, stable BIS values between 40-60 indicate appropriate anesthetic depth 2
• Avoid excessive anesthetic depth (BIS <40) as it may increase the risk of hemodynamic instability and delayed recovery 5
• Avoid BIS values >60 during maintenance as this increases the risk of awareness 2, 3

Special Considerations

• In elderly patients, target BIS values around 50 to reduce postoperative delirium while maintaining adequate anesthesia 4, 5
• Avoid burst suppression patterns (very low BIS values) in elderly patients as this increases the risk of postoperative delirium 5
• Temperature changes during procedures may affect BIS values - hypothermia reduces anesthetic requirements by approximately 1.2 BIS units per 1°C reduction 1
• BIS monitoring should be used as a complement to, not a replacement for, clinical judgment and traditional monitoring methods 1