Awareness Under Anaesthesia

Definition

• Awareness with recall (AWR): conscious experience + explicit episodic memory — clinically significant
• Wakefulness without recall: conscious state during anaesthesia but no subsequent memory — underestimated and more common
• Disconnected consciousness: endogenous experience (dreaming) — not classified as intraoperative awareness

Incidence

• Overall incidence: approximately 1–2 per 1000 cases (0.1–0.2%) under general anaesthesia
• Incidence is higher in specific contexts:
  • Major trauma surgery: historical recall rates up to 43%
  • Cardiac surgery: ~1.5%
  • Caesarean section: ~0.4%
  • Emergency surgery: elevated
• ASA Closed Claims database: ~2% of all claims relate to awareness; approximately 20% of awareness claims were for "awake paralysis" (conscious but paralysed)

Causes and Risk Factors

Patient-Related

• Prior history of intraoperative awareness (strongest individual predictor)
• Morbid obesity
• Chronic substance abuse (alcohol, opioids, benzodiazepines) — increased anaesthetic requirement
• Chronic pain patients with opioid tolerance
• ASA physical status extremes (very sick patients tolerate less)

Surgery-Related

• Major trauma surgery
• Emergency surgery
• Obstetric surgery (especially caesarean section under GA)
• Cardiac surgery
• Procedures requiring "light" anaesthesia for haemodynamic reasons

Anaesthetic Technique-Related

• Inadequate volatile agent delivery (vaporiser malfunction, circuit disconnection)
• Total intravenous anaesthesia (TIVA) — no end-tidal monitor; higher risk
• Neuromuscular blocking agents (NMBAs) — mask clinical signs of inadequate depth (movement); most awareness under paralysis goes unrecognised at the time
• Medication errors (e.g., paralytic administered before induction agent)
• Failure to account for increased requirements (e.g., nitrous oxide as sole agent)
• Reliance on inadequate amnesic techniques

Pathophysiology / Why it Happens

Clinical Presentation

• Auditory perception (hearing conversations)
• Tactile sensation (feeling surgical instruments)
• Pain
• Paralysis and inability to signal (most distressing component)
• Emotional responses (terror, anxiety, helplessness)

• Hypertension, tachycardia
• Sweating, tearing, pupillary dilatation
• Patient movement (masked by NMBAs)

Consequences

Psychological Sequelae

• Mild: anxiety, sleep disturbance, nightmares
• Moderate: phobia of hospitals/future anaesthesia, social withdrawal
• Severe: Post-Traumatic Stress Disorder (PTSD) — occurs in a high proportion of patients who have AWR; may be severe and long-lasting
• Most patients reporting awareness are dissatisfied with how their concerns are managed post-operatively

Detection and Monitoring

1. Isolated Forearm Technique (IFT)

• First described by Tunstall in 1977 for caesarean section
• A tourniquet/BP cuff is inflated to 200 mmHg on one arm before NMBAs are given, isolating that limb from the paralysing effect
• Patient is commanded to "squeeze my hand" — voluntary response indicates wakefulness
• Considered the gold standard for detecting intraoperative consciousness
• Limitations: 30-minute maximum (limb ischaemia), largely remains a research tool
• If a purposeful response → increase hypnotic agent; if reflex movement → increase analgesia

2. EEG-Based Depth of Anaesthesia Monitors

• Bispectral Index (BIS): the most widely studied; a dimensionless number 0–100 derived from processed frontal EEG
  • Target range for GA: 40–60
  • Three RCTs showed BIS helps prevent awareness in high-risk populations, but not superior to an end-tidal anaesthetic gas (ETAG) protocol
  • Not currently recommended for routine use by the ASA
• Spectral entropy, SedLine, Narcotrend: other processed EEG monitors; similar principle
• Key limitation: EEG is a cortical measure, modulated by subcortical arousal systems; NMBAs, hypothermia, and pharmacological effects can confound interpretation

3. End-Tidal Anaesthetic Gas (ETAG) Monitoring

• Maintaining end-tidal volatile agent at ≥0.7–1.0 MAC provides reliable amnesia
• ETAG-guided protocols have been shown to be as effective as BIS in preventing awareness in clinical trials

4. Assessment after Anaesthesia — Brice Interview (Modified)

• Structured post-operative interview to detect unreported awareness:
  1. What is the last thing you remember before going to sleep?
  2. What is the first thing you remember after waking up?
  3. Do you remember anything between these times?
  4. Did you have any dreams during the operation?
  5. What was the worst thing about your operation?

Prevention

1. Preoperative: Identify high-risk patients; counsel appropriately; ensure realistic expectations, especially for monitored anaesthesia care (MAC) and regional anaesthesia
2. Equipment checks: Vaporiser function, circuit integrity, IV line patency before each case
3. Avoid sole reliance on NMBAs without adequate hypnotics
4. TIVA: Use TIVA pumps with anti-siphon and anti-free-flow valves; target-controlled infusion (TCI) with adequate propofol effect-site concentration
5. Volatile agents: Maintain end-tidal concentration consistent with amnesia; ETAG monitoring mandatory
6. Amnesics: Benzodiazepines (midazolam) or scopolamine as adjuncts in high-risk situations where volatile agents cannot be used at full MAC
7. BIS/EEG monitoring: Use in high-risk cases (prior awareness, TIVA, cardiac surgery, obstetric GA)
8. IFT: Consider in patients with prior awareness history or high-risk procedures

Management When Awareness is Suspected or Confirmed

Medico-Legal Aspects

• Awareness claims constitute approximately 2% of ASA Closed Claims cases
• Women undergoing GA without a volatile agent are disproportionately represented in recall claims
• Awake paralysis (paralytic given before induction) is largely preventable with careful drug labelling and sequence checks
• Informed consent for GA should, especially in high-risk procedures, include awareness as a potential risk

Summary Box (Exam Key Points)

Awareness Under Anaesthesia

Definition

• Awareness with recall (AWR): conscious experience + explicit episodic memory — clinically significant
• Wakefulness without recall: conscious state but no subsequent memory — more common, underestimated
• Disconnected consciousness: dreaming under anaesthesia — not classified as true intraoperative awareness

Incidence

• ~2% of ASA Closed Claims Project cases relate to awareness
• ~20% of those claims were for "awake paralysis" (conscious + paralysed, unable to signal)

Causes and Risk Factors

Patient-Related

• Prior history of intraoperative awareness (strongest predictor)
• Morbid obesity
• Chronic substance abuse (alcohol, opioids, benzodiazepines) — increased anaesthetic requirements
• Chronic pain patients with opioid tolerance
• Long-term anxiolytic/sedative use
• Extremes of physiological reserve (very sick patients tolerate less agent)

Surgery-Related

• Major trauma, emergency, obstetric (caesarean GA), cardiac surgery
• Procedures requiring deliberately light anaesthesia (haemodynamic fragility)

Anaesthetic Technique-Related

• Neuromuscular blocking agents (NMBAs) — mask movement, the most reliable clinical sign of inadequate depth
• TIVA without end-tidal monitoring (no MAC equivalent)
• Vaporiser malfunction / circuit disconnection / IV line failure
• Medication errors (e.g., paralytic given before induction agent)
• Nitrous oxide as sole agent
• Failure to increase dose during periods of intense stimulation

Pathophysiology

Clinical Features

What the Patient May Experience

• Auditory perception (hearing voices, surgical sounds)
• Tactile sensation (pressure, instruments)
• Pain
• Inability to move or communicate (most distressing — sense of paralysis and helplessness)
• Emotional distress: terror, panic, anxiety

Intraoperative Signs (may all be absent due to NMBAs or β-blockers)

• Hypertension, tachycardia
• Sweating, lacrimation, pupillary dilatation
• Patient movement

Consequences

• Mild: anxiety, sleep disturbance, nightmares, intrusive memories
• Moderate: fear of future anaesthesia, hospital phobia, social withdrawal
• Severe: Post-Traumatic Stress Disorder (PTSD) — occurs in a high proportion; can be severe and long-lasting
• Most patients reporting awareness are dissatisfied with how their concerns are subsequently managed

Detection

1. Isolated Forearm Technique (IFT)

• First described by Tunstall, 1977 for caesarean section under GA
• BP cuff or tourniquet inflated to ≥200 mmHg on one arm before NMBA administration → isolates limb from paralysis
• Command given: "If you can hear me, open and close the fingers of your right hand"
• Voluntary response = wakefulness confirmed
• Gold standard for detecting intraoperative consciousness in real time
• Limitations:
  • Maximum 30 minutes per application (limb ischaemia risk)
  • Largely remains a research tool
  • Limited access to limbs in some procedures
• If purposeful response → increase hypnotic; if reflex movement → increase analgesia

2. Depth of Anaesthesia Monitors (Processed EEG)

• Bispectral Index (BIS): most studied; dimensionless 0–100 scale derived from frontal EEG
  • Target 40–60 for general anaesthesia
  • Three RCTs showed BIS reduces awareness in high-risk populations — but not superior to ETAG-guided protocols
  • ASA does not currently recommend routine use
• Other monitors: SedLine, Narcotrend, Entropy
• Limitations: affected by NMBAs (reduced EMG artefact → falsely low BIS), hypothermia, pharmacological interference; EEG measures only cortical activity

3. End-Tidal Anaesthetic Gas (ETAG) Monitoring

• Maintaining end-tidal volatile agent at ≥0.7–1.0 MAC reliably produces amnesia
• ETAG-guided protocols are as effective as BIS in clinical trials
• Mandatory monitoring for volatile-based anaesthesia

4. Modified Brice Interview (Post-operative Detection)

1. What is the last thing you remember before going to sleep?
2. What is the first thing you remember after waking up?
3. Do you remember anything in between?
4. Did you dream during the operation?
5. What was the worst thing about the operation?

Prevention

Management When Awareness Occurs

Intraoperatively

• Immediately deepen anaesthesia (increase volatile / propofol bolus)
• Administer benzodiazepine (e.g., midazolam) for anterograde amnesia
• Ensure adequate analgesia
• Document the episode: timing, end-tidal concentrations, drug dosages

Post-operatively

• Conduct modified Brice interview
• Obtain a detailed account of the patient's experience
• Be transparent, empathetic, and non-dismissive — fully answer the patient's questions
• Refer for psychological counselling / PTSD screening and follow-up
• Incident reporting and involvement of risk management if needed
• Litigation awareness: document everything contemporaneously

Medico-Legal Considerations

• Women undergoing GA without a volatile agent are disproportionately represented in recall claims
• "Awake paralysis" is largely preventable with correct drug sequence and labelling checks
• Informed consent for GA should include awareness as a risk, especially in high-risk procedures
• Failure to disclose and manage awareness post-operatively is a major contributor to litigation

Summary for Exam