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More patients than thought are conscious in surgery, especially women – cohort study

The largest study yet on connected consciousness during general anaesthesia suggests that the phenomenon may be more common than initially believed.

General anaesthesia has been around for more than a century, and rarely, patients remain aware under general anaesthesia, and can respond to outside stimuli, like pain.

However, afterwards they cannot recall what happened. This is known as “connected consciousness".

Now, researchers write that it affects one in 10 young adults, and women more than men, reports News24.

The study, published in the British Journal of Anaesthesia, reports that around one in 10 out of the 338 participants, aged 18 to 40, responded to commands while under anaesthesia by squeezing researchers’ hands in response to questions. None remembered this after surgery.

Earlier studies show connected consciousness occurred in 5% of general anaesthetics, but the researchers of this study were concerned that it could be happening more frequently in younger adults and was linked to the patient’s sex.

“There is a need for further research on the biological differences that may influence sensitivity to anaesthetic medication,” said senior author Dr Robert Sanders, an anaesthetist and neuroscientist at the University of Sydney in Australia.

An hour after waking up, participants were asked to recall 16 words they had heard under anaesthesia. Women were two to three times more likely than men to experience “connected consciousness”, they found.

When patients received a continuous level of anaesthesia in the minutes after anaesthesia was induced, and before intubation, the odds of connected consciousness were lower, the team wrote.

Connected consciousness vs anaesthesia awareness

The team pointed out an important difference between connected consciousness and “anaesthesia awareness” (waking up, where the patient can recall their surroundings, or even an event related to the surgery, such as pain, while under general anaesthesia.

But this happens to an even smaller percentage of people – only one or two out of every 1,000 medical procedures, notes the American Society of Anaesthesiologists.

Connected consciousness, on the other hand, means that the patient is only half-paying attention, but is not fully aware. About half of the 37 patients responded to commands that indicated they were in pain.

Lead author, assistant professor Richard Lennertz from the Department of Anaesthesiology at the University of Wisconsin School of Medicine and Public Health, said: “It is important to emphasise the overall safety of anaesthesia.

Patients had no memory of these experiences after surgery. This study highlights an ongoing commitment to patient safety in anaesthesiology and an opportunity for further improvement in patient care.”

Study details

Connected consciousness after tracheal intubation in young adults: an international multicentre cohort study

Richard Lennertz, Kane O. Pryor, Aeyal Raz, Jamie Sleigh, Amy Gaskell, Robert D. Sanders.

Published in the British Journal of Anaesthesia on 23 May 2022


Connected consciousness, assessed by response to command, occurs in at least 5% of general anaesthetic procedures and perhaps more often in young people. Our primary objective was to establish the incidence of connected consciousness after tracheal intubation in young people aged 18–40 yr. The secondary objectives were to assess the nature of these responses, identify relevant risk factors, and determine their relationship to postoperative outcomes.

This was an international, multicentre prospective cohort study using the isolated forearm technique to assess connected consciousness shortly after tracheal intubation.

Of 344 enrolled subjects, 338 completed the study (mean age, 30 [standard deviation, 6.3] yr; 232 [69%] female). Responses after intubation occurred in 37/338 subjects (11%). Females (13%, 31/232) responded more often than males (6%, 6/106). In logistic regression, the risk of responsiveness was increased with female sex (odds ratio [ORadjusted]=2.7; 95% confidence interval [CI], 1.1–7.6; P=0.022) and was decreased with continuous anaesthesia before laryngoscopy (ORadjusted=0.43; 95% CI, 0.20–0.96; P=0.041). Responses were more likely to occur after a command to respond (and not to nonsense, 13 subjects) than after a nonsense statement (and not to command, four subjects, P=0.049).

Connected consciousness occurred after intubation in 11% of young adults, with females at increased risk. Continuous exposure to anaesthesia between induction of anaesthesia and tracheal intubation should be considered to reduce the incidence of connected consciousness. Further research is required to understand sex-related differences in the risk of connected consciousness.


News24 article – ‘Conscious’ under anaesthesia: More common than previously believed (Open access)


See more from MedicalBrief archives:


What it’s like waking up during surgery


Algorithms accurately gauge unconsciousness under general anaesthesia


Nerve stimulation restores some consciousness after 15 years of PVS



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