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Awareness — Risk Factors, BIS, Brice Questionnaire

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Intraop I · 8 min read

Routine cases: 1-2 per 1000. Cardiac, OB, trauma: much higher. End-tidal MAC ≥0.7 or BIS 40-60 — pick one, do it well.

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Identify high-risk awareness scenarios.
Use BIS/SedLine/PSI appropriately.
Prevent awareness with multimodal strategy.
Respond to a patient who reports awareness.

Incidence + risk factors

KeyRoutine GA: 1-2 per 1000 cases.

Higher-risk groups

cardiac surgery (~1%)
OB emergency C-section under GA (~1%)
trauma (up to 10%)

Common thread: hemodynamic instability constrains anesthetic depth.

Other risk factors

chronic opioid + benzo + ketamine users (tolerance)
history of awareness
TIVA without depth monitoring
MAC <0.7 by clinical necessity
paralyzed for the case (no motor signs to alert)
female sex
age <60
ASA 3-5
light-anesthetic intentional plans

Document predictors in the pre-op note and the plan that mitigates them.

Awareness during anesthesia: risk factors include light anesthesia, paralysis, TIVA misuse, cardiac/OB/trauma cases; prevention with adequate dosing, depth monitoring, MAC awareness.

B-Aware → BAG-RECALL — what the trials actually showed

KeyB-Aware (Myles et al, Lancet 2004): BIS-guided GA in high-risk patients cut awareness vs standard practice established BIS as protective.

B-Unaware (Avidan, NEJM 2008): BIS-guided vs end-tidal-anesthetic-concentration (ETAC) guided — equivalence.

BAG-RECALL (2011, NEJM): same equivalence in larger high-risk cohort.

Clinical reading: either protocol-driven monitoring works (BIS 40-60 OR ETAC ≥0.7 MAC); the discipline of the protocol matters more than the technology.

Both clearly beat no-protocol practice.

Processed EEG (BIS) clinical pearls/pitfalls: don't rely on BIS alone for awareness prevention - use minimum MAC and benzodiazepines in high-risk cases; check signal quality, EMG artifact, electrode placement; correlate with clinical signs and end-tidal anesthetic concentration.

BIS 40-60 vs end-tidal ≥0.7 MAC — when to pick which

End-tidal MAC

free with any modern machine
universally available
evidence-equivalent in most settings

Default for volatile-based balanced anesthesia.

BIS adds value when you can't get a useful MAC reading: TIVA (no end-tidal volatile), cardiac/critical cases tolerating MAC <0.7 by necessity, MH-trigger-free anesthetic with TIVA in MH-susceptible patient.

Limitations of BIS

lag 15-30 sec
EMG + cautery artifact
unreliable with ketamine + N₂O + dexmedetomidine (all alter EEG without proportional sedation)
cerebral injury or low temperature distorts

Don't toggle between monitors mid-case — pick one and commit.

Processed EEG (BIS) limitations - overview/definitions: BIS does not reliably correlate with ketamine, nitrous oxide, or dexmedetomidine anesthesia; can be falsely elevated by EMG signal or low by hypothermia. Not a definitive awareness monitor; complements clinical assessment.

Common process failures that drive awareness

KeySpecific recurring patterns in closed-claims awareness: (1) syringe swap — intended induction agent was actually muscle relaxant.

Empty/failed vaporizer — refill before light cases, check level pre-induction.

Disconnect at start of case before connection to ventilator.

IV infiltration — TIVA drug going into tissue instead of vein.

Underdosed RSI in unstable patient + immediate emergence not anticipated.

Wrong-volatile-channel (sevo dialed up but ETT goes through machine still on standby).

Mitigation

end-tidal MAC alarm on
BIS as backup
vigilance during the first 5 min + first incision (peak awareness windows)

Vaporizer filling errors: wrong agent fill (incorrect concentration delivery and patient risk), overfilling (liquid in fresh gas line, high concentration), spillage/tip risk; always check agent, fill level, and secure mounting.

Modified Brice questionnaire

KeyPost-op screening for explicit recall.

Five questions, asked at 24 hr + 7 days + 30 days (recall sometimes delayed): (1) What is the last thing you remember before falling asleep?

What is the first thing you remember on waking up?

Do you remember anything in between?

Did you dream during the procedure?

What was the worst part of the experience?

Positive screen = explicit recall of intra-op events

Sensitivity high; specificity lower (dreams + PACU memories misclassified).

Confirm with detailed structured interview + chart review by the M&M committee or designated reviewer.

When awareness occurs — disclosure + PTSD prevention

KeyAcknowledge + validate the patient's experience without minimization.

Document the Brice findings + your conversation.

Notify surgeon, risk management, and provide written ASA awareness brochure.

Arrange psychological evaluation within 1-2 weeks — PTSD develops in 30-50% of awareness victims without intervention.

Open disclosure + structured follow-up significantly reduces PTSD.

QI: bring case to M&M, identify the process failure (one of the patterns above), implement systems change.

Patient should be flagged for awareness-prophylaxis protocol at any future anesthetic.

Pressure (decubitus) injury prevention in the OR: risk factors (long case, hypotension, diabetes, low albumin), staging (I-IV), and intervention bundle - padding bony prominences, repositioning, head/heel/sacrum/elbow attention.

Adjunct strategies in high-risk cases

Cardiac surgery

scopolamine 0.4 mg IV pre-bypass (amnestic)
midazolam 0.05 mg/kg supplements
BIS-guided depth during low-MAC pump time
isoflurane on bypass via oxygenator (target gas-analyzer concentration)

Trauma

ketamine 0.5 mg/kg supplements during massive transfusion (preserves hemodynamics + adds amnesia)
scopolamine if anticipating need for low MAC
midazolam after stabilization

OB emergency C-section GA

brief midazolam 1-2 mg after cord clamp (avoid before — neonatal depression)
ketamine 0.5 mg/kg
ensure ETAC ≥1 MAC after delivery

Across all high-risk: never substitute paralytic for anesthetic.

Paralyzed-but-awake is the worst-case scenario.

Volatile anesthetic pharmacokinetics - Compound A: sevoflurane + dry CO2 absorber forms Compound A (fluoromethyl-difluorovinyl ether) with theoretical renal toxicity; mitigate with fresh gas flow >=2 L/min and moist absorbers.

⚠ Common pitfalls

Trusting BIS alone in ketamine, N₂O, or dexmedetomidine cases — false readings.
Skipping depth monitoring during TIVA with paralysis — highest awareness risk.
Dismissing a patient's awareness report — long-term PTSD implications.
Aiming for BIS 40-60 in elderly without considering frailty — burst suppression risk.

💎 Clinical pearls

Awareness incidence ~0.1-0.2% overall; ~1% in cardiac, OB, trauma — higher in these.
BAG-RECALL trial: BIS-guided vs ETAC-guided showed equivalent awareness rates; both work.
Brice questionnaire post-op for high-risk cases — early detection allows early support.
If awareness reported: validate, document, refer to psych — do NOT dismiss as dream.

Recap

Awareness incidence ~0.1-0.2% overall; ~1% in cardiac, OB, trauma — higher in these.
BAG-RECALL trial: BIS-guided vs ETAC-guided showed equivalent awareness rates; both work.
Brice questionnaire post-op for high-risk cases — early detection allows early support.
If awareness reported: validate, document, refer to psych — do NOT dismiss as dream.

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