Anaesthesia awareness or intraoperative awareness is a situation in which the patient is partially awake during a surgery. How common are such incidences and what are potential problems associated?
Previous estimates were at 1 in a 1000 patients (1‰) suffer from intraoperative awareness:
The medical literature suggests that in- traoperative awareness with recall while under general anesthesia may occur to some degree at a frequency of approximately 1 – 2 in 1,000 anesthetics. Most patients experiencing intraoperative awareness do not feel any pain.
Source: American Association of Nurse Anaesthetists, Patient Awareness Brochure.
However, the 5th National Audit Project (NAP5) conducted a study on accidental awareness during general anaesthesia in 2014 with the largest test group so far found that incidents were as low as 1 in 19.000 cases. This huge project has been compiled into a book (with the chapters available as PDF here), below are just some extracts:
Source: 5th National Audit Project of The Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland: Accidental Awareness during General Anaesthesia in the United Kingdom and Ireland. Report and findings of the 5th National Audit Project, Chapter 6, p. 40. 2014
However, not all incidents were accompanied with pain or distress:
The proportion of patients judged to have experienced distress at the time of the AAGA increased with Michigan score (Figure 7.5): distress was most common when pain and paralysis were experienced together, with 17 of 22 patients reporting distress (77%).
Source: 5th National Audit Project of The Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland: Accidental Awareness during General Anaesthesia in the United Kingdom and Ireland. Report and findings of the 5th National Audit Project, Chapter 7, p. 51. 2014
This means that of the on-average 0.0051% cases of AAGA, only 77% reported distress, and of those 77%, 80% experienced pain and paralysis, the sort of locked-in-experience that is presented in most newspapers.
The actual chance of such a locked-in-experience is thus 0.0031%.
Values taken from: National Safety Council, What Are the Odds of Dying From..., 2017. nsc.org.