Awareness Under Anaesthesia and Depth of Anaesthesia Monitoring

Quick Answer

Accidental awareness during general anaesthesia (AAGA) is a rare but devastating complication with an incidence of approximately 1:19,000 anaesthetics in the UK (NAP5 data). It is defined as explicit recall of sensory perceptions during intended general anaesthesia. Risk factors include patient factors (female sex, young age, previous awareness, difficult airway), surgical factors (cardiac surgery, caesarean section, major trauma), and anaesthetic factors (total intravenous anaesthesia without depth monitoring, neuromuscular blockade, light anaesthesia for haemodynamic instability). Consequences can be severe, with 51% of patients experiencing psychological sequelae including PTSD, anxiety, and depression.

Depth of anaesthesia (DOA) monitors, including bispectral index (BIS), entropy, and auditory evoked potentials, use processed electroencephalography (EEG) to provide a numerical index of hypnotic depth. The NAP5 audit found that patients who received end-tidal anaesthetic concentration (ETAC) monitoring with a target of ≥0.7 MAC, or BIS-guided anaesthesia with target 40-60, had the lowest awareness risk. Current evidence from the B-Aware and BAG-RECALL trials suggests BIS monitoring reduces awareness during high-risk TIVA but provides no additional benefit over ETAC monitoring during volatile anaesthesia.

Prevention Strategy:

• Pre-induction machine and drug check
• ETAC monitoring with target ≥0.7 MAC for volatile anaesthesia
• BIS monitoring (target 40-60) for high-risk cases and all TIVA
• Minimise use of neuromuscular blockade where possible
• AAGA checklist for high-risk patients
• Prompt investigation and support if awareness suspected

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Definitions

Awareness with Explicit Recall

Definition: Conscious perception of events during general anaesthesia with subsequent explicit (declarative) memory formation, allowing the patient to recall specific details when questioned postoperatively.

Characteristics:

• Patient can describe sensory experiences (auditory, tactile, visual)
• May recall conversations, surgical events, or environmental sounds
• Memory is accessible to conscious retrieval
• Most commonly reported: auditory perceptions (voices, sounds) > tactile (pain, paralysis) > visual
• Classified by Brice questionnaire responses [PMID: 2658468, PMID: 24836920]

Modified Brice Questionnaire:

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 your operation?
5. What was the worst thing about your operation?

Awareness without Explicit Recall (Implicit Memory)

Definition: Processing of intraoperative information without conscious recall, demonstrated by changes in behaviour or performance on psychological tests.

Characteristics:

• Patient has no conscious memory of events
• May exhibit psychological effects without knowing cause
• Demonstrated experimentally through priming tasks
• Clinical significance uncertain; may contribute to unexplained postoperative behavioural changes
• Cannot be detected by standard questioning [PMID: 9523802]

Detection Methods (Research):

• Word stem completion tasks
• Perceptual identification tasks
• Preference tasks
• Category generation tests

Dreaming During Anaesthesia

Definition: Subjective experience of dream content during general anaesthesia, reported by 20-40% of patients.

Characteristics:

• Distinguished from awareness by absence of accurate recall of intraoperative events
• Content usually pleasant or neutral; rarely distressing
• May be confused with awareness if dream content involves surgical themes
• More common with ketamine, propofol, and light anaesthesia
• Does not constitute true awareness unless dream accurately reflects real events
• Not associated with psychological sequelae in most cases [PMID: 15310346, PMID: 21282398]

Differentiation from AAGA:

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Epidemiology and Incidence

NAP5 Data (5th National Audit Project)

The NAP5 audit (2011-2012) was the largest prospective study of awareness, providing the most accurate incidence data for general anaesthesia-related awareness. [PMID: 25316645, PMID: 25104234]

Key Findings:

Patient Demographics (NAP5):

• Female: 63% of awareness cases (RR 1.5-2.0)
• Mean age: 45 years (younger patients at higher risk)
• ASA 3-5: 40% of cases (sicker patients)
• Previous awareness: 8% reported prior episode

Clinical Circumstances:

• 75% of cases occurred during induction or emergence
• 46% associated with problems at induction
• 25% occurred during maintenance
• Paralysis without adequate hypnosis most common scenario

Historical Context

Pre-NAP5 Incidence Estimates:

Reason for Discrepancy:

• Earlier studies used structured questioning (higher detection)
• NAP5 relied on spontaneous reporting (under-reporting likely)
• True incidence likely 1:1,000 to 1:5,000 when systematically sought
• Methodology differences significant [PMID: 15310349, PMID: 10781463]

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Risk Factors

Patient Factors

Strongly Associated:

Possible Associations:

• Red hair (MC1R gene variants): anecdotal, may require higher volatile concentrations
• ASA 3-5 status: haemodynamic compromise limits anaesthetic depth
• Anxiety: heightened awareness, possible memory consolidation effects [PMID: 24836920, PMID: 25316645]

Surgical Factors

High-Risk Surgery:

Obstetric Anaesthesia (GA Caesarean Section):

• Pre-delivery: Light anaesthesia to avoid fetal depression (0.5 MAC, no opioid)
• Rapid sequence induction with limited time for assessment
• Highest reported incidence: 0.4% (1:250) in some series
• Post-delivery deepening reduces but does not eliminate risk
• NAP5: Caesarean section awareness rate 1:670 (all GA) [PMID: 25316645, PMID: 8259223]

Anaesthetic Factors

Technique-Related:

TIVA-Specific Risks:

• No breath-by-breath feedback of drug delivery (unlike ETAC)
• IV line disconnection/occlusion may go undetected
• Pump programming errors
• Drug dilution errors
• Syringe swap errors
• Patient factors affecting pharmacokinetics (obesity, renal/hepatic impairment)

NAP5 Key Finding: TIVA without processed EEG monitoring had higher awareness incidence than volatile anaesthesia with ETAC monitoring. Recommendation: All TIVA cases should have DOA monitoring. [PMID: 25316645]

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Consequences of Awareness

Psychological Sequelae

The NAP5 audit documented significant psychological morbidity following awareness:

Immediate Effects:

• Acute distress during event: 65%
• Pain: 43%
• Paralysis (most distressing): 55%
• Attempted movement: 31%
• Feeling of dying/suffocation: 19%

Long-Term Sequelae (NAP5):

Post-Traumatic Stress Disorder (PTSD):

• Full PTSD criteria met in 20-35% of awareness cases
• Symptoms: flashbacks, nightmares, avoidance, hypervigilance
• May develop weeks to months after event
• Paralysis during awareness strongest predictor of PTSD
• Requires specialist psychological treatment
• May never fully resolve in severe cases [PMID: 10781463, PMID: 18227325, PMID: 22618539]

Predictors of Severe Psychological Sequelae:

• Pain experienced during awareness
• Paralysis with inability to signal distress
• Duration of awareness
• Pre-existing psychological vulnerability
• Perceived helplessness
• Delayed recognition and support

Medicolegal Implications

Awareness is a significant source of medicolegal claims against anaesthetists.

Claim Data:

• 2-3% of all anaesthesia malpractice claims
• Average settlement: AUD $50,000-150,000 (varies by jurisdiction)
• Successful claims increasing despite unchanged incidence
• Psychological injury claims often exceed physical injury claims

Legal Considerations:

• Duty of care: Reasonable standard of monitoring and drug delivery
• Informed consent: Awareness risk should be mentioned in high-risk cases
• Documentation: Record anaesthetic depth (ETAC, BIS), drug doses, clinical signs
• Response: Prompt recognition, apology, support, and documentation

Defensible Practice:

• Follow institutional guidelines and checklists
• Use appropriate monitoring (ETAC ≥0.7 MAC or BIS 40-60)
• Document anaesthetic depth throughout procedure
• Investigate and document any suspected awareness
• Offer psychological support and follow-up [PMID: 23823774, PMID: 28426523]

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Depth of Anaesthesia Monitors

Bispectral Index (BIS)

Technology: BIS (Medtronic/Covidien) is the most widely studied and used DOA monitor, providing a dimensionless index from 0 (isoelectric EEG) to 100 (fully awake).

Signal Processing:

1. Single frontal EEG channel acquisition (FP1-Fpz or equivalent)
2. Artefact rejection (EMG, electrical interference)
3. Fast Fourier transform for frequency analysis
4. Bispectral analysis (phase coupling between frequencies)
5. Burst suppression detection
6. Algorithm combines multiple parameters into single index

BIS Components:

• Beta ratio: Log (P30-47Hz / P11-20Hz) - higher with awareness
• SynchFastSlow: Bispectral measure of phase synchronisation
• Burst suppression ratio: Percentage of isoelectric epochs
• QUAZI suppression index: Nearly suppressed activity

Target Ranges:

Evidence for BIS:

• B-Aware trial: 82% reduction in awareness with BIS monitoring in high-risk patients [PMID: 15306525]
• BAG-RECALL trial: No difference between BIS and ETAC-guided anaesthesia for volatile agents [PMID: 21555826]
• Meta-analyses: Benefit in high-risk patients and TIVA; no benefit over ETAC for volatile [PMID: 27541145]

Entropy (GE Healthcare)

Technology: Entropy monitoring uses spectral entropy analysis of the EEG to measure irregularity (unpredictability) of the signal.

Components:

• State Entropy (SE): 0.8-32 Hz, reflects cortical activity (hypnotic component)
• Response Entropy (RE): 0.8-47 Hz, includes frontal EMG (higher frequencies)
• RE-SE difference: >10 suggests inadequate analgesia (EMG activation)

Entropy Values:

Advantages:

• Provides separate indices for hypnosis (SE) and EMG activity (RE)
• RE-SE difference may indicate nociception/lightening
• Similar performance to BIS in clinical studies

Evidence:

• Comparable to BIS for awareness prevention
• RE-SE difference correlates with inadequate analgesia
• Limited large-scale RCT data compared to BIS [PMID: 17389817, PMID: 15166300]

Narcotrend (MonitorTechnik)

Technology: German-developed monitor using pattern recognition of EEG stages, based on Loomis and Kugler sleep EEG classifications.

Narcotrend Stages:

Advantages:

• Visual EEG display with classification
• Raw EEG always visible for interpretation
• Good performance in paediatric patients
• CE marked; widely used in Europe

Evidence:

• Comparable to BIS in preventing awareness
• Validated in adults and children
• Limited RCT data; primarily observational studies [PMID: 12693967, PMID: 16616305]

Auditory Evoked Potential (AEP) Monitors

Technology: AEP monitors measure the brain's electrical response to auditory stimuli (clicks), assessing the integrity of auditory processing pathways.

AEP Components:

• Brainstem AEP (BAEP): 0-10 ms latency; unaffected by anaesthesia
• Middle latency AEP (MLAEP): 10-100 ms; affected by anaesthetic depth
• Late cortical AEP (LCAEP): >100 ms; abolished by surgical anaesthesia

AEP Index (AAI):

• Derived from MLAEP amplitude and latency
• Range 0-100 (similar to BIS)
• Target range: 15-25 for adequate anaesthesia
• Requires auditory stimulation (headphones)

Advantages:

• Directly measures auditory pathway (awareness is often auditory)
• May detect impending awareness earlier than EEG-based monitors
• Less affected by EMG artefact

Disadvantages:

• Requires continuous auditory stimulation
• Hearing impairment affects validity
• More complex setup
• Limited by signal averaging delay

Evidence:

• A-Line AEP monitor demonstrated awareness reduction in one RCT
• Less widely studied than BIS
• Not widely available in current practice [PMID: 9474520, PMID: 16782909]

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How Processed EEG Works

EEG Basics

Electroencephalography Fundamentals: The EEG records electrical activity from the cerebral cortex, primarily reflecting postsynaptic potentials of pyramidal neurons.

Signal Characteristics:

• Amplitude: 10-200 microvolts (10-200 μV)
• Frequency: 0.5-50 Hz (clinically relevant)
• Generated by synchronised activity of cortical pyramidal cells
• Volume conduction to scalp electrodes

EEG Frequency Bands:

EEG Changes with Anaesthetic Depth:

Processing Algorithms

Time Domain Analysis:

• Amplitude measures (mean, peak)
• Burst suppression ratio (percentage of suppressed epochs)
• Zero crossing frequency

Frequency Domain Analysis (Spectral Analysis):

• Fast Fourier Transform (FFT) converts time-domain signal to frequency spectrum
• Power spectral density: distribution of signal power across frequencies
• Spectral edge frequency (SEF95): frequency below which 95% of power lies
• Median frequency: frequency dividing spectrum in half

Bispectral Analysis:

• Examines phase coupling between different frequency components
• Quadratic phase coupling indicates non-linear interactions
• Bicoherence: normalised measure of phase coupling
• Unique to BIS; reflects cortical interactions

Entropy Analysis:

• Shannon entropy: measure of signal irregularity/unpredictability
• Highly ordered signals (like sine waves) have low entropy
• Complex, irregular signals (awake EEG) have high entropy
• Anaesthesia reduces entropy as EEG becomes more regular

Algorithm Integration:

• Multiple parameters combined using proprietary algorithms
• Weighting coefficients derived from large databases
• Continuous recalculation (typically every 1-5 seconds)
• Smoothing applied to reduce artefact influence [PMID: 10534463, PMID: 11081507]

Limitations

EMG Artefact:

• High-frequency (>30 Hz) signals from facial muscles
• Can falsely elevate BIS values (mistaken for beta activity)
• Occurs with: inadequate neuromuscular blockade, pain, light anaesthesia
• Paradoxically, paralysis can unmask true low BIS values
• EMG artefact indicator on BIS monitor should be monitored [PMID: 11081507]

Ketamine:

• Produces dissociative anaesthesia with paradoxically high BIS values (70-90)
• EEG shows beta activation despite unconsciousness
• DO NOT rely on BIS alone for ketamine-based anaesthesia
• May combine with propofol/volatile for reliable monitoring [PMID: 12571267]

Paediatric Patients:

• Neonatal and infant EEG differs from adult patterns
• Higher amplitude, slower frequencies at baseline
• Age-specific algorithms required but limited validation
• BIS may overestimate depth in infants <1 year
• Use with caution; clinical signs remain important [PMID: 12693967, PMID: 17478456]

Neurological Conditions:

• Dementia, cerebral palsy, epilepsy affect baseline EEG
• May produce spuriously low or high values
• Interpret in clinical context
• Cannot rely solely on processed EEG

Other Limitations:

• Hypothermia: Reduces BIS values independently of anaesthetic depth
• Hypoglycaemia: May produce EEG changes
• Cerebral ischaemia: Produces burst suppression
• Electrical interference: Operating room equipment, cautery
• Signal quality indicator should be green before interpreting values

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Evidence for DOA Monitoring

B-Aware Trial (2004)

Study Design:

• Prospective, randomised, double-blind
• 2,463 high-risk patients (cardiac, trauma, rigid bronchoscopy, caesarean, ASA 4-5)
• BIS-guided anaesthesia (target 40-60) vs routine care
• Primary outcome: Definite awareness (Brice questionnaire)

Results:

• Awareness: BIS group 2 (0.17%) vs control 11 (0.91%)
• Relative risk reduction: 82% (p=0.022)
• Number needed to treat (NNT): 138
• First RCT demonstrating BIS reduces awareness in high-risk patients

Limitations:

• High-risk population only
• Standard care group not protocolised
• Small absolute numbers of awareness
• Cannot extrapolate to routine, low-risk anaesthesia [PMID: 15306525]

BAG-RECALL Trial (2011)

Study Design:

• Prospective, randomised, assessor-blinded
• 5,713 patients at high awareness risk
• BIS-guided (target 40-60) vs ETAC-guided (target ≥0.7 MAC) volatile anaesthesia
• Primary outcome: Definite or possible awareness

Results:

• Awareness: BIS group 7 (0.24%) vs ETAC group 2 (0.07%)
• No significant difference (p=0.98)
• BIS group numerically more awareness (not statistically significant)
• ETAC-guided anaesthesia non-inferior to BIS

Conclusions:

• For volatile anaesthesia with ETAC monitoring, BIS provides no additional benefit
• ETAC ≥0.7 MAC is protective against awareness
• BIS value lies in TIVA and situations without ETAC monitoring

Key Difference from B-Aware:

• BAG-RECALL had ETAC-protocolised control group
• B-Aware control group had no specific depth protocol
• Demonstrates importance of any depth monitoring, not specifically BIS [PMID: 21555826]

Michigan Awareness Control Study (MACS)

Findings:

• Electronic anaesthetic record review of 185,000 cases
• 0.0068% incidence of awareness (much lower than NAP5)
• BIS monitoring associated with reduced awareness (OR 0.51, 95% CI 0.26-0.99)
• Effect strongest in high-risk patients
• Supports role of BIS but not as sole strategy [PMID: 23823774]

NAP5 Recommendations

Based on the comprehensive NAP5 audit, the following recommendations were made for awareness prevention: [PMID: 25316645, PMID: 25104234]

For Volatile Anaesthesia:

• Monitor end-tidal anaesthetic concentration (ETAC) in all cases
• Maintain ETAC ≥0.7 age-adjusted MAC (prevents awareness in vast majority)
• DOA monitoring optional but may add safety margin

For TIVA:

• Use processed EEG monitoring (BIS, entropy) for all TIVA cases
• Target BIS 40-60 or equivalent
• Cannot rely on clinical signs alone (especially with NMB)
• Consider ETAC monitoring during TIVA (confirms lack of volatile, may add awareness drug if fail)

For High-Risk Cases:

• Cardiac surgery, obstetric (GA), major trauma, ASA 4-5
• Consider DOA monitoring even with volatile
• Use AAGA checklist preoperatively
• Document depth parameters throughout

General Recommendations:

• Minimise neuromuscular blockade where possible
• Ensure functioning anaesthetic delivery systems
• Maintain vigilance during induction and emergence
• Post-operative interview for suspected awareness

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Prevention Strategies

AAGA Checklist

A structured checklist for awareness prevention, particularly for high-risk cases:

Pre-Induction:

• Anaesthetic machine checked; vaporizer filled
• TIVA pumps programmed correctly; lines patent
• Neuromuscular monitoring available
• DOA monitor available and electrodes applied (if indicated)
• High-risk patient identified; technique planned

Induction:

• Adequate induction dose administered
• Loss of consciousness confirmed before paralysis
• Anaesthetic delivery commenced (volatile or TIVA running)
• ETAC or BIS confirms adequate depth before intubation

Maintenance:

• ETAC ≥0.7 MAC or BIS 40-60 continuously
• Clinical signs monitored (HR, BP, sweating, lacrimation)
• NMB level assessed; avoid excessive paralysis
• Any lightening addressed promptly

Emergence:

• Anaesthesia not discontinued until surgery complete
• NMB reversed adequately
• Spontaneous ventilation before extubation (if possible)
• Post-operative visit planned

Adequate Dosing

Induction:

• Propofol: 1.5-2.5 mg/kg (reduce in elderly, increase in young)
• Thiopental: 3-5 mg/kg
• Confirm loss of eyelash reflex and verbal response before NMB
• Allow adequate time for drug effect (arm-brain circulation time)

Maintenance (Volatile):

• Target ETAC ≥0.7 age-adjusted MAC
• Account for age reduction in MAC (6-7% per decade after 40)
• Add N2O 50-70% as adjunct if tolerated
• Supplemental opioid for analgesia

Maintenance (TIVA - Propofol/Remifentanil):

• Propofol target-controlled infusion (TCI): Marsh 3-6 μg/mL effect-site
• Remifentanil TCI: Minto 2-8 ng/mL effect-site
• Titrate to BIS 40-60
• Reduce propofol in elderly, hepatic impairment

Alarm Settings

BIS Monitor:

• Set low alarm: 40 (to avoid excessive depth)
• Set high alarm: 60 (to alert to potential awareness)
• Audio alarm must be audible

ETAC Monitoring:

• Set low alarm: 0.7 MAC (minimum acceptable for awareness prevention)
• Respond promptly to low ETAC alarms

Agent Analyser:

• Monitor inspired and expired anaesthetic concentrations
• Alarms for low/absent agent detection

Equipment and Drug Verification

Pre-Use Checks:

• Vaporizer filled and functional
• TIVA pumps tested, programmed correctly
• IV lines patent, no disconnections
• Anaesthetic circuit integrity confirmed

Intraoperative Vigilance:

• Regular visual confirmation of drug delivery
• Check TIVA pump rate and remaining volume
• Verify vaporizer dial setting matches intended dose
• Respond to any alarms immediately

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Management of Suspected Awareness

Intraoperative Recognition

Signs Suggestive of Awareness (Without NMB):

• Purposeful movement
• Eye opening, tears
• Swallowing, coughing
• Grimacing

Signs Suggestive of Lightening (With or Without NMB):

• Tachycardia (>20% increase from baseline)
• Hypertension (>20% increase)
• Sweating
• Lacrimation
• Pupil dilation
• BIS >60 or rising trend

Isolated Forearm Technique (IFT):

• Tourniquet placed on arm before NMB given
• Forearm muscles not paralysed; patient can move fingers
• Can request hand squeeze to confirm consciousness
• Research tool; not routine practice [PMID: 24836920]

Immediate Response to Suspected Awareness

If Awareness Suspected Intraoperatively:

1. Deepen anaesthesia immediately:

   • Bolus propofol 50-100 mg or thiopental 50-100 mg
   • Increase volatile concentration
   • Give opioid bolus (fentanyl 50-100 μg)

2. Reassure verbally:

   • Calmly state "You are having an operation. You are safe. We are looking after you."
   • Even if uncertain if patient can hear, verbal reassurance is harmless and potentially beneficial

3. Consider benzodiazepine:

   • Midazolam 1-2 mg IV may induce anterograde amnesia
   • Does not "erase" existing memories but may prevent consolidation
   • Ethically debated; some consider it attempting to cover up event

4. Document event:

   • Time of suspected awareness
   • Clinical signs observed
   • BIS/ETAC values
   • Actions taken

Postoperative Management

Immediate Post-Operative Visit:

• See patient within 24 hours
• Use modified Brice questionnaire
• Ask open-ended questions; avoid suggesting awareness
• Listen carefully and empathetically
• Do not dismiss or minimise concerns

If Awareness Confirmed:

1. Acknowledge and apologise:

   • Express genuine empathy: "I am very sorry this happened to you."
   • Explain what may have occurred
   • Do not be defensive; open disclosure

2. Document thoroughly:

   • Patient's account verbatim
   • Anaesthetic record review
   • Any equipment checks performed
   • Plan for follow-up and support

3. Offer psychological support:

   • Early psychological referral (within 2 weeks)
   • Trauma-focused cognitive behavioural therapy (TF-CBT) is effective
   • May require long-term therapy for PTSD
   • Support groups may be helpful

4. Report and review:

   • Local incident reporting system
   • Root cause analysis if indicated
   • Consider equipment testing
   • ANZCA Webairs reporting (Australia)

5. Plan for future anaesthesia:

   • Document awareness clearly in medical record
   • Recommend DOA monitoring for all future GAs
   • Consider regional/neuraxial alternatives
   • Provide letter for patient to carry [PMID: 25316645, PMID: 22618539]

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Medicolegal Aspects

Standard of Care

Current Standard (Australia/New Zealand):

• ETAC monitoring considered mandatory for volatile anaesthesia
• DOA monitoring (BIS/entropy) strongly recommended for TIVA
• NAP5 recommendations widely accepted as best practice
• Failure to follow guidelines may be considered breach of duty

Documentation Requirements:

• Anaesthetic technique and drug doses
• Depth parameters (ETAC, BIS) at regular intervals
• Clinical response to surgical stimulation
• Any suspected awareness and actions taken

Open Disclosure

Australian National Open Disclosure Standards:

• Awareness is a notifiable adverse event
• Honest, timely communication with patient
• Expression of regret ("sorry this happened")
• Explanation of investigation and actions
• Support and follow-up offered

Elements of Disclosure:

• What happened (factual account)
• How it happened (if known)
• Actions to be taken
• Support available
• Apology does not constitute admission of liability (in most Australian jurisdictions)

Risk Management

Proactive Measures:

• Follow NAP5/institutional guidelines
• Use appropriate monitoring for technique
• Document depth parameters
• Preoperative discussion of awareness risk in high-risk cases

Reactive Measures:

• Prompt investigation of suspected awareness
• Open disclosure with patient
• Psychological support referral
• Equipment testing and root cause analysis
• Incident reporting for system learning

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander peoples, as well as Maori in New Zealand, may face specific considerations regarding awareness under anaesthesia and depth of anaesthesia monitoring that require culturally informed care.

Health Disparities and Access: Aboriginal and Torres Strait Islander Australians experience higher rates of comorbidities including cardiovascular disease, diabetes, renal disease, and obesity that may increase anaesthetic complexity. These conditions can affect drug pharmacokinetics and may necessitate dose adjustments that could impact awareness risk. Higher prevalence of chronic pain and opioid use in some communities may increase tolerance and awareness risk if standard doses are insufficient.

Access to surgery in remote and rural areas may involve lengthy transfers to regional centres, with anaesthetic services potentially having limited access to advanced monitoring such as processed EEG devices. Ensuring equity of care requires that depth of anaesthesia monitoring be available for high-risk cases regardless of location.

Cultural Safety in Communication: If awareness occurs in an Aboriginal or Torres Strait Islander patient, the psychological impact may be compounded by historical trauma, distrust of healthcare systems, and different cultural understanding of medical experiences. Involvement of Aboriginal Health Workers (AHWs) and Aboriginal Liaison Officers (ALOs) in post-operative communication is essential. Family and community may need to be involved in discussions according to the patient's wishes and cultural protocols.

For Maori patients in Aotearoa New Zealand, the concept of wairua (spiritual wellbeing) may be particularly affected by awareness experiences. Involvement of whanau (extended family) and Maori health workers in post-event support is important. Te Whare Tapa Wha model (addressing tinana, hinengaro, whanau, and wairua) should guide holistic support.

Recommendations for Culturally Safe Practice:

• Ensure equity of access to DOA monitoring regardless of geographical location
• Pre-operative assessment should include cultural considerations and interpreter services if required
• If awareness suspected, early engagement of cultural support services
• Follow-up must accommodate community and family obligations
• Documentation should respect cultural preferences while ensuring medicolegal requirements met
• Consider remote community follow-up via telehealth if patient has returned home

[PMID: 29024541, PMID: 32165945]

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SAQ Practice Question

Question (20 marks)

ANZCA Final Examination Written Paper

A 35-year-old woman is scheduled for emergency laparotomy for blunt abdominal trauma following a motor vehicle accident. She is haemodynamically unstable with a blood pressure of 80/50 mmHg despite fluid resuscitation, and is estimated to have lost 2 litres of blood. She is awake and anxious, repeatedly asking "Will I feel anything during the operation?"

(a) Identify the specific risk factors for accidental awareness during general anaesthesia (AAGA) in this patient. (5 marks)

(b) Describe the depth of anaesthesia monitoring options available and their relative merits for this patient. (5 marks)

(c) Outline your anaesthetic technique and specific strategies to minimise awareness risk while maintaining haemodynamic stability. (6 marks)

(d) After the operation, the patient reports possible awareness. Describe your immediate and long-term management. (4 marks)

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Model Answer

(a) Risk Factors for AAGA (5 marks)

Patient Factors:

• Female sex (1.5-2× higher awareness risk)
• Young age (35 years; faster drug metabolism, higher requirements)
• Anxiety and heightened awareness (may enhance memory consolidation)

Surgical Factors:

• Emergency trauma surgery (NAP5: 2-3× higher risk than elective)
• Major trauma with haemodynamic instability (limits anaesthetic dose)
• Likely rapid sequence induction (limited time for assessment)

Anaesthetic Factors:

• Haemodynamic instability mandates light anaesthesia to avoid cardiovascular collapse
• Likely requirement for neuromuscular blockade (masks signs of lightening)
• Possible TIVA use if haemodynamic instability precludes volatile agents
• High catecholamine state may increase anaesthetic requirements
• Time pressure and clinical urgency may limit depth monitoring setup

NAP5 Data: Major trauma awareness incidence reported as 1:100-1:500, substantially higher than elective surgery (1:19,600).

(b) Depth of Anaesthesia Monitoring Options (5 marks)

Bispectral Index (BIS):

• Most widely validated DOA monitor
• Provides 0-100 index; target 40-60 for surgical anaesthesia
• Advantages: Easy application, continuous display, evidence for awareness reduction in high-risk patients (B-Aware trial)
• Limitations in this case: May be falsely elevated by EMG artefact (pain response, shivering), ketamine (if used) produces paradoxically high values despite unconsciousness
• Recommended if TIVA planned (no ETAC feedback)

End-Tidal Anaesthetic Concentration (ETAC):

• Measures volatile agent delivery breath-by-breath
• Target ≥0.7 age-adjusted MAC protective
• Advantages: Already integrated into standard monitoring, no additional electrodes required, validated by NAP5 and BAG-RECALL
• Limitations: Only applicable for volatile anaesthesia; does not measure consciousness directly
• Preferred if volatile anaesthesia feasible

Entropy (SE/RE):

• Similar to BIS; may provide additional information via RE-SE difference
• Comparable accuracy to BIS
• Less widely available than BIS

Clinical Signs:

• Heart rate, blood pressure, sweating, lacrimation, pupil size
• Unreliable in trauma (catecholamine surge, haemodynamic instability)
• Even less reliable with neuromuscular blockade
• Not sufficient as sole awareness indicator in this high-risk patient

Recommendation: Use BIS monitoring in addition to ETAC if volatile used, or BIS essential if TIVA required due to haemodynamic instability.

(c) Anaesthetic Technique and Awareness Prevention Strategies (6 marks)

Pre-Induction:

• Apply BIS monitoring before induction
• Prepare vasopressors (noradrenaline infusion) to support blood pressure during induction
• Have blood products immediately available
• Brief team: "High awareness risk patient; will prioritise depth monitoring"

Induction:

• Ketamine 1-2 mg/kg IV: Provides analgesia and amnesia with cardiovascular stability
• Alternative: Reduced propofol dose (0.5-1 mg/kg) with midazolam 1-2 mg for amnesia
• Add opioid cautiously (fentanyl 1-2 μg/kg) for blunting intubation response
• Rocuronium for rapid sequence (not suxamethonium if possible - avoid fasciculation effects)
• Confirm loss of consciousness before paralysis if time permits

Maintenance:

• Prefer volatile agent (sevoflurane/desflurane) if haemodynamics tolerate: target ETAC ≥0.7 MAC
• If TIVA required: Low-dose propofol TCI (2-3 μg/mL effect-site) titrated to BIS 40-60
• Add ketamine infusion 0.25-0.5 mg/kg/hr for opioid-sparing and amnestic effect (note: BIS unreliable with ketamine)
• Benzodiazepine (midazolam 2-5 mg) for anterograde amnesia
• Minimise neuromuscular blockade to what is surgically necessary

Specific Strategies:

• Vasopressor/inotrope support allows adequate anaesthetic dosing without hypotension
• Target-controlled transfusion to restore circulating volume
• Accept higher heart rate/BP during light anaesthesia rather than hypotension with excessive depth
• Continuous BIS monitoring with alarm at 60; respond immediately to rising values
• Verbal reassurance intermittently (patient may be processing even if unconscious)
• N2O 50-70% as adjunct if FiO2 requirements permit (reduces volatile/TIVA requirement)

(d) Management of Suspected Awareness (4 marks)

Immediate Management (within 24 hours):

• Visit patient personally; allow her to describe experience without prompting
• Use modified Brice questionnaire: "What is the last thing you remember before falling asleep? What is the first thing you remember after waking? Do you remember anything in between?"
• Listen empathetically; do not dismiss or minimise
• Acknowledge distress: "I am very sorry you had this experience."
• Review anaesthetic record: BIS values, ETAC, drug doses, documented events
• Document her account verbatim in medical record

Open Disclosure:

• Explain what is known about what occurred
• Describe any factors that may have contributed (haemodynamic instability requiring light anaesthesia)
• Offer apology and express empathy (not admission of liability)
• Explain support available

Psychological Support:

• Early referral to psychologist/psychiatrist experienced in trauma (within 2 weeks)
• Explain possibility of PTSD and importance of treatment
• Offer follow-up contact and ongoing support
• Provide patient information resources (AAGBI awareness leaflet)

Long-Term Management:

• Document awareness clearly in permanent medical record
• Letter to GP detailing event and recommendations for future anaesthesia
• Provide patient with card/letter to present to future anaesthetists
• Recommend DOA monitoring for all future general anaesthetics
• Consider regional/neuraxial alternatives where possible
• Incident report to local system and ANZCA Webairs
• Root cause analysis if system factors identified

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Viva Scenario

Opening Stem

Examiner: You are the consultant anaesthetist called to assess a 45-year-old woman who reported possible awareness to the PACU nurse following a laparoscopic cholecystectomy. The anaesthesia was provided by a trainee under distant supervision using a TIVA technique with propofol and remifentanil. No depth of anaesthesia monitor was used. The patient is tearful and anxious.

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Expected Dialogue

Examiner: What are your initial concerns?

Candidate: This is a serious situation requiring immediate attention. My concerns are:

1. For the patient: She may have experienced awareness, which is a distressing event with potential for significant psychological sequelae including PTSD. She needs empathetic support, information, and access to psychological services.

2. For the system: TIVA without depth of anaesthesia monitoring is a recognised risk factor for awareness (NAP5 data). This represents a potential gap in practice that needs to be addressed.

3. For the trainee: They need support, education about the incident, and understanding that awareness can occur despite best practice, though DOA monitoring may have helped.

4. For documentation and disclosure: This needs to be handled appropriately for patient welfare and medicolegal protection.

Examiner: How would you approach the patient?

Candidate: I would approach her promptly, within the PACU if she is stable, ensuring privacy and adequate time.

My approach would be:

• Introduce myself as the consultant anaesthetist
• Acknowledge that I understand she has concerns about what she experienced during the operation
• Use the modified Brice questionnaire to systematically enquire:
  • "What is the last thing you remember before falling asleep?"
  • "What is the first thing you remember after waking up?"
  • "Do you remember anything in between these two points?"
  • "Did you dream during your operation?"
  • "What was the worst thing about your operation?"
• Listen carefully and allow her to describe experiences in her own words
• Not interrupt or suggest details
• Document her account verbatim

Examiner: She describes hearing voices talking about the surgery and feeling pressure in her abdomen but no pain. She couldn't move or open her eyes. How do you interpret this?

Candidate: This description is consistent with awareness with explicit recall.

Key features supporting awareness:

• Auditory perceptions (hearing voices) - the most common awareness modality
• Tactile sensations (pressure) correlated with surgical events
• Paralysis (couldn't move) - likely reflecting neuromuscular blockade
• Unable to signal distress (couldn't open eyes)

This pattern - sensory awareness with paralysis - is particularly distressing and strongly associated with subsequent PTSD (NAP5 data: paralysis was the strongest predictor of psychological sequelae).

The absence of pain suggests some analgesic effect (likely from remifentanil), but the lack of amnesia indicates inadequate hypnotic depth.

Examiner: What do you tell her?

Candidate: I would communicate with empathy and honesty:

"Thank you for telling me about your experience. I am very sorry this happened to you. What you are describing sounds like you may have been aware during part of your operation. This is a rare but recognised complication of general anaesthesia.

I understand how distressing this must have been, especially not being able to move or communicate. You are safe now, and the surgery was completed successfully.

We take this very seriously. I want to ensure you receive appropriate support. Some people experience ongoing distress after an experience like this, and there are effective treatments available.

I will review the anaesthetic record in detail to understand what happened. I will arrange for you to see a psychologist who specialises in this area. I will also provide you with information about what to expect and how to access support.

Do you have any questions? Is there anything I can do for you right now?"

Examiner: Review of the anaesthetic record shows propofol TCI 3-4 μg/mL effect-site, remifentanil 3-4 ng/mL, rocuronium 50 mg at induction with no repeat doses. What are your observations?

Candidate: Several observations from the record:

Propofol dosing:

• 3-4 μg/mL effect-site is within typical range but on the lower end
• In a 45-year-old woman, this may be inadequate, particularly without BIS confirmation
• Individual variation in propofol sensitivity is substantial
• NAP5 found higher awareness risk with low-end TIVA dosing

Absence of DOA monitoring:

• This is a significant factor
• NAP5 strongly recommends processed EEG monitoring for all TIVA
• Without BIS/entropy, there was no objective measure of hypnotic depth
• TIVA awareness incidence 1:8,000 with monitoring approaches 1:4,000-1:5,000 without

Remifentanil:

• Provides excellent analgesia (patient reported no pain)
• Does NOT provide hypnosis or prevent awareness at typical doses
• May mask signs of lightening (no hypertension/tachycardia response)

Neuromuscular blockade:

• Single dose of rocuronium; likely still partially paralysed during period of awareness
• Paralysis prevented movement that might have alerted anaesthetist
• Classic awareness scenario: paralysed without adequate hypnosis

Likely mechanism: Inadequate propofol effect-site concentration (possibly due to patient factors or dosing) with paralysis preventing movement as a warning sign, compounded by absence of DOA monitoring.

Examiner: What are the medicolegal implications?

Candidate: There are several medicolegal considerations:

Standard of Care:

• NAP5 recommendations are widely accepted as best practice
• DOA monitoring for TIVA is strongly recommended (approaching standard of care)
• Failure to use BIS/entropy for TIVA may be considered below expected standard
• However, awareness can occur even with optimal monitoring

Defensibility:

• Documentation of anaesthetic technique and dosing is important
• Absence of DOA monitoring during TIVA is a vulnerability
• Prompt acknowledgment, open disclosure, and support are protective
• Attempting to minimise or deny the event would be detrimental

Open Disclosure:

• Awareness is a notifiable adverse event
• Honest communication with patient is required
• Apology ("sorry this happened") is appropriate and not admission of liability
• Document disclosure conversation

Incident Reporting:

• Report to local incident management system
• Consider reporting to ANZCA Webairs
• Root cause analysis may be indicated
• Focus on system improvement, not blame

Trainee Support:

• Trainee needs support and education
• Awareness can occur despite reasonable practice
• However, learning opportunity regarding DOA monitoring importance
• Consultant bears ultimate responsibility for supervision standard

Risk Mitigation:

• Ensure patient has psychological support
• Document all communications
• Review departmental TIVA protocols
• Consider whether guideline or equipment change required

Examiner: What recommendations would you make for the department?

Candidate: Based on this event and NAP5 evidence, I would recommend:

Equipment:

• Ensure DOA monitors (BIS, entropy) available in all theatres
• Consider mandating DOA monitoring for all TIVA cases

Protocols:

• Update departmental TIVA protocol to require processed EEG monitoring
• Develop AAGA checklist for high-risk cases
• Establish ETAC targets ≥0.7 MAC for volatile anaesthesia

Education:

• Case-based teaching on awareness risk factors and prevention
• Trainee education on DOA monitoring interpretation
• Awareness of NAP5 recommendations

Support:

• Establish pathway for psychological support following suspected awareness
• Contact with experienced psychologist identified
• Patient information resources available

Reporting:

• Clear incident reporting pathway
• Regular audit of awareness reports
• M&M discussion of this case (anonymised)

Long-term:

• Consider participation in national awareness reporting
• Regular review of departmental awareness incidence
• Quality improvement initiatives

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Last updated: February 2026 | Next review: February 2027 ANZCA PS26: Guidelines on Consent for Anaesthesia or Sedation NAP5: 5th National Audit Project on Accidental Awareness during General Anaesthesia