How can the risk of intraoperative awareness under general anesthesia be minimized?

Minimizing the Risk of Intraoperative Awareness Under General Anesthesia

Processed EEG monitoring should be used when total intravenous anesthesia (TIVA) is administered with neuromuscular blockade to prevent intraoperative awareness under general anesthesia. 1

Understanding Intraoperative Awareness

Intraoperative awareness under general anesthesia (AAGA) is a serious complication that can lead to significant psychological trauma, including post-traumatic stress disorder in up to 50% of affected patients 2. While the reported incidence varies across studies, it ranges from as low as 0.0068% 3 to approximately 0.1-0.2% 2 in the general population, with higher rates in high-risk patients.

Key Risk Factors for Intraoperative Awareness

1. Use of neuromuscular blocking agents (NMBs)

   • The vast majority of definite or probable cases occur during anesthetics involving NMBs 1
   • NMBs prevent patients from signaling awareness while conscious

2. Total intravenous anesthesia (TIVA)

   • Lack of reliable monitoring to confirm drug delivery to the patient 1
   • No end-tidal concentration monitoring available (unlike with inhalational agents)

3. Phases of anesthesia

   • Almost two-thirds of AAGA cases occur before the start or after the end of surgery 1
   • Induction and emergence are particularly vulnerable periods

4. Inadequate anesthetic dosing

   • Underdosing due to hemodynamic concerns
   • Failure to adjust dosing based on individual patient needs

Evidence-Based Prevention Strategies

1. Processed EEG Monitoring

• For TIVA with neuromuscular blockade: Processed EEG monitoring should be used 1
• For TIVA without NMBs: Processed EEG monitoring should be considered 1
• For inhalational anesthesia: May have a role in reducing AAGA, particularly during induction and emergence 1
• Implementation details:
  • Start monitoring before induction
  • Continue at least until full recovery from NMB effects is confirmed
  • Target BIS range of 40-60 during maintenance 1
  • Don't rely solely on index values; understand basic EEG waveforms and power spectral analysis 1

2. End-Tidal Anesthetic Concentration (ETAC) Monitoring

• For inhalational anesthetics: Monitor ETAC whenever inhaled anesthetics are used 1
• Target: Maintain ETAC > 0.7 age-adjusted MAC during maintenance 1
• Implementation details:
  • Enable audible alarms for low ETAC (< 0.7 age-adjusted MAC) 1
  • Use monitors with direct age-adjusted MAC alarm capability 1

3. Neuromuscular Monitoring

• Essential when using NMBs 1
• Implementation details:
  • Use quantitative neuromuscular monitoring devices
  • Apply monitor before administering NMBs
  • Confirm adequate recovery (ToF ratio > 0.9) before awakening and extubation
  • Prefer ulnar nerve monitoring; if using facial nerve, revert to ulnar nerve at end of surgery 1

4. Anesthetic Agent Selection and Administration

• Avoid benzodiazepines in ERAS pathways to allow rapid awakening 1
• Use short-acting agents such as propofol for induction 1
• For propofol infusions: Avoid abrupt discontinuation to prevent rapid awakening with anxiety and agitation 4
• For high-risk patients: Consider slower induction, titrated to clinical responses 4

Special Considerations

High-Risk Patients

• Cardiac patients: Use slower rates of administration in hemodynamically unstable patients 4
• Neurosurgical patients:
  • Avoid rapid boluses that could decrease cerebral perfusion pressure
  • Use slow bolus (approximately 20 mg every 10 seconds) or infusion 4
  • Consider hyperventilation and hypocarbia when increased ICP is suspected 4

Monitoring During Critical Periods

• Induction and emergence: These are particularly high-risk periods for awareness 1
• Patient transfers: Maintain the same standard of monitoring during transfers as in the operating room 1

Common Pitfalls to Avoid

1. Relying solely on clinical signs to assess anesthetic depth
2. Overreliance on single monitoring modality (combine ETAC and processed EEG when possible)
3. Inadequate monitoring during induction and emergence (two-thirds of awareness cases occur during these periods)
4. Failure to use quantitative neuromuscular monitoring when administering NMBs
5. Abrupt discontinuation of propofol infusions leading to rapid awakening 4

By implementing these evidence-based strategies, the risk of intraoperative awareness under general anesthesia can be significantly reduced, improving patient safety and preventing potentially devastating psychological consequences.