Anaes · Depth of anaesthesia & awareness
Depth of anaesthesia & awareness
Also known as Depth of anaesthesia · Awareness under anaesthesia · Accidental awareness · NAP5 · Bispectral index · Processed EEG · Implicit awareness · Explicit recall
The depth of anaesthesia and the awareness under anaesthesia concern the assurance of the unconsciousness and the amnesia, and the prevention of the traumatic awareness. The framework rests on the components of the anaesthetic depth (the hypnosis, the immobility, the analgesia), the definition and the types of the awareness (the explicit, the implicit, the pain, the recall), the NAP5 (the incidence and the risk factors), the processed EEG (the BIS and the entropy) and the evidence (the B-Unaware and the BAG-RECALL trials), the high-risk situations (the paralysed, the TIVA, the cardiac, the caesarean, the trauma), the psychological consequences and the follow-up, and the prevention.
Practise this topic
On this page
Study tools
Your progress
Saved on this device.
Target exams
Red flags
- The accidental awareness under the general anaesthesia is the rare (about 1 in 19 600 in NAP5; 1 in 8 200 with neuromuscular blockade) but the psychologically-traumatic complication, the most-feared by the patients. The highest risk in the paralysed patient, the TIVA, the cardiac, the caesarean, the trauma, the difficult airway, the light anaesthesia for the haemodynamic compromise. The prevention: the adequate dosing, the avoidance of the muscle relaxant without the hypnotic, the monitoring (the processed EEG in the high-risk), the alarm for the vaporiser failure, and the structured follow-up of any report.
Meet the patient
A thirty-four-year-old woman is intubated for an emergency caesarean under rapid sequence induction. Hours later, in recovery, she tells the nurse she could hear the surgeons arguing and felt she could not move or breathe. She is shaking, and she is telling the truth.[6]
This is the scenario NAP5 was built to capture — a paralysed patient, light anaesthesia kept for the neonate, and an explicit memory that will outlive the operation. NAP5 cases were overwhelmingly unintended awareness during neuromuscular blockade, and three-quarters of obstetric awareness in Odor's cohort arose at induction or emergence. Hold the question every awareness case turns on, was the patient paralysed, and was there a hypnotic on board when she was?, and the rest of the topic falls into place.[8][6]
References12ShowHide
- [1]Yu H, et al. Depth of anesthesia monitoring: Current evidence, clinical impact, and future directions J Int Med Res, 2026.PMID 42333677
- [2]Berger-Estilita J, et al. Making brain monitoring routine: why processed EEG monitoring should be standard practice J Clin Monit Comput, 2026.PMID 42247119
- [3]Rieck E, et al. The potential of processed EEG monitoring systems in predicting postoperative cognitive deficits J Clin Anesth, 2026.PMID 42160881
- [4]Graham M, et al. Minimizing the Harm of Accidental Awareness Under General Anesthesia: New Perspectives From Patients Misdiagnosed as Being in a Vegetative State Anesth Analg, 2018.PMID 28922237
- [5]Pandit JJ, et al. Movements During Intended General Anesthesia and Psychologically Traumatic Accidental Awareness: Explanatory Role of the Efference Copy Network Anesth Analg, 2026.PMID 40911489
- [6]Odor PM, et al. Incidence of accidental awareness during general anaesthesia in obstetrics: a multicentre, prospective cohort study Anaesthesia, 2021.PMID 33434945
- [7]Sury MR, et al. Accidental awareness during anesthesia in children Paediatr Anaesth, 2016.PMID 27059416
- [8]Pandit JJ, et al. 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: summary of main findings and risk factors Br J Anaesth, 2014.PMID 25204697
- [9]Avidan MS, et al. Anesthesia awareness and the bispectral index N Engl J Med, 2008.PMID 18337600
- [10]Avidan MS, et al. Prevention of intraoperative awareness in a high-risk surgical population N Engl J Med, 2011.PMID 21848460
- [11]Cook TM, et al. 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: patient experiences, human factors, sedation, consent, and medicolegal issues Br J Anaesth, 2014.PMID 25204696
- [12]Aasheim A, et al. Association of Age, Sex and ASA Physical Status With Bispectral Index Values During General Anaesthesia: A Large Observational Cohort Study Acta Anaesthesiol Scand, 2026.PMID 42289314