Accidental awareness under anesthesia (AAUA) has long been regarded as an uncommon complication in the operating room. Yet for the small percentage of patients who experience it, AAUA can leave lasting psychological scars. As evidence grows about its underlying risk factors and impact, European clinicians and surgical teams face a significant mandate: prevention, preparation, and comprehensive support for affected patients.

AAUA is postoperative recall of intraoperative events or responsiveness to commands despite anesthesia, the latter known as “connected consciousness.” Its toll is far from minor, encompassing acute traumatic experiences and long-term sequelae like posttraumatic stress, nightmares, and anxiety.

It occurs in roughly 0.1%-0.2% of surgical patients — meaning hundreds of thousands worldwide each year. But a 2023 meta-analysis of 64 studies and nearly 100,000 patients found that the risk is not evenly distributed, with women being more vulnerable to the experience.

Why Are Some Patients at Higher Risk?

According to the meta-analysis, not only there were more confirmed cases of postoperative recall among women than among men but also women exhibited higher mean intraoperative responsiveness. Also, in one study but not another, women were reported to require higher doses of propofol for the anesthesia to be effective.

Physiologic differences may play a role: Women in the reviewed studies had higher processed EEG readings during surgery, indicating lighter states of anesthesia.

Beyond gender, other risk factors have emerged.

“It’s an important issue of concern to anesthetists and patients alike,” said Philip Barclay, MBBS, honorary senior clinical lecturer at Imperial College London and consultant anesthetist at Chelsea and Westminster Hospital NHS Foundation Trust, both in London, England. Drawing on findings from the fifth National Audit Project (NAP5) and subsequent 2019 UK guidelines, Barclay identified key risk domains:

• Patient factors: Emergency surgery, obesity, difficult airway, female sex, and young adulthood
• Anesthetic factors: Rapid sequence induction for patients at risk for pulmonary aspiration, neuromuscular blockade, and total intravenous (IV) anesthesia
• Organizational factors: Out-of-hours operations or the involvement of junior anesthetists

High-risk specialties include obstetrics — where C-sections combine multiple risk factors — and cardiothoracic surgery, where lower drug doses are sometimes used due to cardiac vulnerability. Additional guidance by the UK’s Royal College of Anaesthetists links low blood pressure and the use of muscle relaxants — which inhibit patient movement or signaling — to elevated AAUA risk.

Intriguingly, the phenomenon might have a neurobiological basis as well. A 2023 study by Trinity College Dublin researchers found that patients who experienced AAUA tended to have larger volumes of frontal gray matter and stronger frontoparietal brain connections, potentially supporting continued conscious experience despite general anesthesia.

Why Does Accidental Awareness Occur?

Understanding why AAUA happens is critical for prevention. Careful, individualized evaluation before surgery can help flag patients with high susceptibility.

Vincent Bonhomme, MD, PhD, professor at Liege University Hospital in Liege, Belgium, emphasized that episodes of connected consciousness during anesthesia — whether accompanied by explicit recall — may be due to insufficient hypnotic anesthetic dosing, which can occur accidentally (as with an IV line detachment or empty vaporizer) or may be intentional for clinical reasons, as during a C-section or in frail patients. Some individuals are also naturally resistant to certain anesthetics, especially those on chronic liver enzyme-inducing medications.

Bonhomme also distinguishes between two scenarios:

• Episodes with explicit recall: Less common, but potentially more distressing, occurring in fewer than 1 in 1000 procedures. The risk is associated more with patient fragility, the use of chronic disease medications, a previous episode, or specific procedures like C-sections.
• Episodes without explicit recall: Detected more often, in up to 4.6% of procedures, and typically recognized only if the patient does not receive muscle relaxants or with techniques like the isolated forearm method. In this technique, inflating a blood pressure cuff above systolic pressure preserves movement in one arm after neuromuscular blockade; finger movement in response to command can signal intraoperative awareness.

Prevention: Systematic, Team-Based Approaches

Preventing AAUA calls for detailed presurgical evaluation and a team-wide commitment to perioperative safety. Bonhomme stressed the need for anesthetists to specifically screen for risk factors of connected consciousness. Maintaining vigilance over potential triggers — such as inadequate drug doses or the presence of medications that affect anesthetic metabolism — is central.

Institutional safety measures are equally vital. A 2023 study by researchers in the UK, Switzerland, Ireland, Denmark, and Slovakia underscored the value of practices like:

• Standard drug trolley setups
• Ensuring all staff are familiar with updated operating theater protocols
• Ready access to patient medical records during procedures
• Regular anesthetic simulation training for staff
• Maintaining easily accessible difficult airway equipment

Managing the Aftermath: Supporting and Investigating

When AAUA is suspected or confirmed, swift, structured action is needed. Five steps summarize current best practice:

• Immediate medical support: Anesthetists must carefully monitor for signs of intraoperative awareness throughout the perioperative period and act according to established protocols.
• Routine screening: Use structured tools like the Brice questionnaire to prospectively identify unreported cases because patients may be reluctant to volunteer details.
  • “What’s the last thing you remember before anesthesia?”
  • “What’s the first thing you remember after?”
  • “Do you recall anything in between?”
• Proper debriefing: Validation is essential. If the patient describes explicit recall, their experience must be acknowledged and not dismissed. Teams should provide consistent, empathetic communication, and patients should be encouraged to recount events in their own words, detailing the nature (auditory, tactile, painful, or paralysis) of their sensations.
• Timely referral: Referral to psychological support may be indicated, especially when symptoms persist. A 2-week follow-up is standard, with further referral for formal assessment if needed. Even asymptomatic patients should be advised to seek help if issues arise later.
• Thorough analysis: After patient debriefing, the event must be reviewed to identify causes, using frameworks like NAP5 classifications and correlating patient reports with anesthetic charts. A multidisciplinary group — unbiased and specialized — should lead this inquiry to inform future prevention.

Above all, transparency and patient-centered communication must guide the response to AAUA.

“A reasonable explanation for why accidental awareness occurred should be provided to the patient,” Bonhomme advised. Clinicians should reassure individuals that recurrence is not inevitable and ensure documentation is complete for future care.

AAUA remains rare, but its impact is powerful. As research clarifies both risk and remedy, a culture of proactive prevention and compassionate follow-up will be the best safeguard for patients placed under anesthesia.

Barclay reported having no relevant financial relationships.

Bonhomme reported receiving support for research, honoraria, and consultancy from Orion Pharma, Medtronic, Edwards Lifesciences, Grünenthal, and Elsevier.