Awareness under Anaesthesia

Awareness under anesthesia (AUA), or accidental awareness during general anesthesia (AAGA), is a rare (0.1% to 0.2% in low-risk surgeries) but can rise to 1–2% in high-risk cases (e.g., cardiac surgery, trauma, or cesarean sections) . Proper assessment is critical to diagnose AUA, evaluate psychological sequelae, and guide management.

1. Initial Clinical Assessment

Structured Interviews

The Brice Interview is the gold standard for detecting AUA postoperatively. It includes:

  1. "What was the last thing you remembered before going to sleep?"

  2. "What was the first thing you remembered after waking up?"

  3. "Did you dream or have other experiences during the procedure?"

  4. "What was the worst thing about your operation?"

  5. "What was the next worst thing?" .

    • This method identifies explicit recall and distinguishes AUA from dreams or emergence delirium.

Modified Brice Questionnaire

Expands on the Brice Interview to include:

  • Sensory details (e.g., auditory, tactile, pain).

  • Emotional impact (e.g., fear, helplessness) .

2. Psychological and Trauma Assessment

Post-Traumatic Stress Disorder (PTSD) Screening

Up to 70% of AUA patients develop psychological sequelae, including PTSD (10–25%) . Tools include:

  • PTSD Checklist (PCL-5): Assesses intrusion, avoidance, and hyperarousal symptoms.

  • Impact of Event Scale-Revised (IES-R): Evaluates distress related to traumatic recall .

Michigan Awareness Classification Instrument (MACI)

Classifies AUA severity:

  • Class 0: No recall.

  • Class 1: Isolated auditory perceptions.

  • Class 2: Tactile awareness (e.g., pressure, tube sensations).

  • Class 3: Pain or distress.

  • Class 4: Paralysis with terror ("awake paralysis") .

    • A "D" modifier denotes psychological distress (e.g., "Class 3D") .

3. Objective Monitoring and Scoring Systems

Depth of Anesthesia (DoA) Metrics

  • Bispectral Index (BIS):

    • EEG-based score (40–60 = adequate anesthesia;

    • <40 = deep sedation;

    • >60 = risk of awareness) .

  • End-Tidal Anesthetic Concentration (ETAC): Measures volatile anesthetic delivery (e.g., MAC >1.0 reduces AUA risk) .

  • Auditory Evoked Potentials (AEP): Monitors brainstem response to sounds (Pk = 0.80–0.94 for detecting consciousness) .

Limitations

  • BIS reliability is reduced with ketamine, nitrous oxide, or EEG abnormalities .

  • No single tool is 100% sensitive; multimodal monitoring is recommended.

4. Documentation and Follow-Up

  • Medico-legal documentation: Detail anesthetic doses, equipment checks, and intraoperative vital signs .

  • Referrals: Psychology/psychiatry for PTSD, sleep clinics for nightmares, and support groups .

  • Prevention for future surgeries: Use of benzodiazepines pre-op, avoidance of neuromuscular blockers if possible, and DoA monitoring .

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