Awareness Under General Anesthesia

Mechanisms of AUGA

• Our monitors are still limited in assessing brain function to monitor anesthetic effects on our neurobiology, leading to a lack of ability to expressly monitor for awareness under anesthesia.¹
• While there is limited understanding of the neurobiological pathways underlying intraoperative awareness, the pathways of wakefulness have been well described in the locus coeruleus, tuberomammillary nucleus, hypothalamus, pontine reticular formation, dorsal raphe nucleus, and prefrontal cortex.
• Given the complexity of wakefulness and memory formation, not all intraoperative awareness is equivalent, and the Michigan Awareness Classification Instrument was developed to stratify AUGA.

• The incidence of awareness is approximately 0.1 – 0.2% of cases, and in about 20% published case reports, patients were able to identify voices.

Risk Factors and Reducing AUGA

• AUGA is most common at induction and emergence of general anesthesia
  • Difficult airway placement prolongs the induction phase and delays the delivery of maintenance anesthetics (total intravenous anesthesia (TIVA)/volatile) and increases the likelihood of awareness.
• Several risk factors are associated with AUGA, including surgical type, anesthetic choice, and patient characteristics.3
  • Surgical risk factors
    • Emergent surgery (trauma, Cesarean delivery)
    • Prolonged airway/difficult airway placement
    • Cardiopulmonary bypass cases
  • Anesthetic risk factors
    • Neuromuscular blockade (NMB) significantly increases the risk (1:82000 w/NMB vs 1:135900 w/o NMB)  16-fold increase3
    • TIVA
      • Absence of a reliable means to monitor anesthetic concentrations
        • Human pump error, IV failure, etc.
      • Even with target-controlled infusions and processed electroencephalogram (EEG), TIVA still results in intraoperative awareness at the target values for each, respectively.
    • Light anesthetics
    • Rapid sequence inductions and intubations
  • Patient risk factors
    • History of awareness
    • Acute hemodynamic compromise
    • Chronic substance use -> acquired resistance to anesthetics
    • Smoking

Reducing AUGA is a complex and incomplete field of study.

• First and foremost, minimizing the anesthesia risks listed above and ensuring adequate delivery of anesthesia at induction and throughout the case are paramount.
• EEG monitoring has gained popularity and has demonstrated good correlation with wakefulness and depth of anesthesia; however, few studies have sufficient power to accurately assess whether AUGA can be prevented.
• The utility of EEG monitoring (BIS, Entropy, Narcotrend, Patient State Analyzer, SNAP index, SedLine) has yielded mixed results: some reports that BIS reduces awareness by up to 82% (B-Aware Trial, 2004), whereas others show no significant difference (NCT00281489, 2008).
  • The US Food and Drug Administration states that the “Use of BIS monitoring to help guide anesthetic administration may be associated with the reduction of the incidence of awareness and recall in adults during general anesthesia and sedation.”⁵

Sequelae of AUGA

• If AUGA is suspected intraoperatively, the American Society of Anesthesiology guidelines recommend the immediate administration of a benzodiazepine, with the caveat that benzodiazepines do not have reliable retrograde recall prevention.³
  • Deepening the anesthetic and confirming the administration of the appropriate anesthetic is paramount.
• If the patient demonstrates AUGA postoperatively, a structured interview at several times. should be performed:
  • Immediate assessment in PACU: focus on what they can recall in detail
    • Do not dismiss any of the patient’s concerns, but be empathetic and listen.
  • 1 day postoperatively: many AUGA events do not happen until hours or days after the event
  • 1 month after the event, assess the patient to determine whether they require psychological or other support.
• The surgical and nursing teams should be informed of AUGA; similarly, the patient may find it helpful to meet with these teams, separately or together, to express their thoughts and concerns.
• The most common complaints of AUGA were auditory perception (66%), followed by inability to move (34%), sensation/weakness/paralysis (17%), pain (38%), and feelings of helplessness, panic, anxiety, and catastrophe (34%).⁴
• Postoperative sequelae include
  • Sleep disturbances (19%)
  • Nightmares (21%)
  • Fear of future anesthetics (20%)
  • Daytime anxiety (17%)
  • PTSD (71%)⁶