What Happens to the Unconscious Brain Under Anesthesia During Surgery? Dreaming and Awareness with Recall

What does the brain do during surgery with general anesthesia? It is pretty clear that it keeps many autonomic  bodily function going well, because the anesthetist monitors these very closely to make sure the depth of anesthetic does not shut down anything needed to keep the patient alive, and that anything compromised to some degree (respiration, for example) is carefully supplemented.  A more interesting question might be: What  is the mind up to?

Two interrelated brain-mind phenomena in patients undergoing surgery under the influence of anesthesia have  stimulated a good deal of ongoing study: dreaming with recall, and awareness with recall.

Studies suggest that the overall percentage of patients who dream and can recall their dreams ranges  from about 22% if they are questioned about it within an hour or two post-surgically, with progressively lower rates (down to 2%-4%) reported if the patients are interviewed days or weeks later. Virtually all authorities suggest that patient memories of having dreamed, and their content of most of these dreams, are not long retained.

Commentators suggest that since very few anesthesia rooms use EEG monitors that can independently detect dreaming activity, the willingness of the patients to admit to dreaming and their willingness to discuss their dreams is likely to bias   survey results. Analyses tend to conflict somewhat in terms of the gender of the more likely dreamer, but tend to agree on the age range, body type, and certain common lifestyle indicators.

Young fit, thin females having relatively short surgical procedures are cited one study of nearly 7,000 patients as the most likely candidates for dream recall, in one Swedish study. But an Australian & New Zealand study of 300 patients points to younger active males, and suggests that people who dream during regular sleep and can remember it, seem much more likely to report that they dreamt and can recall the content of the dream after surgery.

One interesting finding is that women are more likely to report dreaming after the fact of surgery, if they were anxious about their surgery prior to the operation, a trend not noticed as readily in men. 

What do most patients who report dreaming, dream about? Work, family and recreational activities appear most common by far, although Victorian-era reports of anesthesia obsessed that anesthetics might induce a higher percentage of, or more vivid, dreaming about having sex, that could have unfortuante consequences for all concerned..

A 2007 article in Anesthesiology (106: 1232-1326) included a detailed study of  multiple cases of surgeons and dentists being accused of sexually assaulting women in the period from 1849-1888, largely because the women under anesthesia appeared to have had dreams of having sex with the doctor.

While not ruling out the possibility that such an abuse can happen, the authors document accusations that resulted in convictions that in hindsight (or with closer contemporary examination of circumstances : e.g.  a vividly detailed claim by a female patient during a dental extraction that the dentist had sex with her, despite the fact that the husband, who testified for the dentist, was in the dental surgery room during the entire procedure) suggested that the practitioners clearly deserved the benefit of at least reasonable doubt. The conclusion of the article is a timely warning to all those who use anesthesia in their practice, that in light of the frequency of dreams with sexual content in women, (that is not intended as a sexist remark: for reasons yet to be explained, there really are few recorded complaints coming from men) it is mandatory to have a third party in the vicinity for the protection of both patient and practitioner.

Apart from the above instance, one of the more worrisome possibilities is that people will dream about their surgeries and confuse what they dreamt happened to them in vivid terms of gore, pain, or surgical catastrophes for what actually happened. The literature suggests that this does happens in a small number of cases (2-3% of surgeries).  But when the patients  eventually realize, sometimes on their own, and sometimes with reassurance from doctors or recovery room nurses, that the content was in fact a dream, and not an actual experiencing of the procedure, the memory of the dream fades and any negative emotional impact goes with it. Their satisfaction with the surgeon and the surgery appear to be unaffected,   and both are rated positively on post-operative questionnaires.

In less than 1% of surgeries, despite the best efforts of anesthesiologists, patients are undeniably able to recall with great accuracy the details of their surgeries. While the reasons for this continue to be under ongoing investigation, it seems more likely to occur under certain surgical situations when the deepest level of anesthesia is not in the larger  interest of the patient ----trauma surgery, heart surgery, and caesarian sections where it would harm the baby. Some studies which used the more standardized measure of depth of anesthesia, called the BiSpectral Index or BIS, rather than the impressionistic reports of the anesthetist,   give results that conflict with the working hypothesis that comparative shallowness of anesthesia leads to more dreaming or more actual awareness.

The types of anesthetic and adjuvant medications used show some, but not a clear cut,  correlation to the risk of vivid dreaming with recall and actual awareness with recall. A Spanish study of 4001 patients disclosed somewhat greater risk of awareness with recall for   O2/NO2 based anesthesia, and suggested that halogenated anesthetics and the use of benzodiazepines (tranquilizers) reduce that   risk. An Italian study claims that scopolamine injected intramuscularly flat-out prevents dreams altogether.

One of the few studies designed to determine whether or not a given anesthetic at low doses might still be able to   block extremely unpleasant memories, such as those connected with surgery was conducted at U.Cal.Irvine.  Volunteers were given .001, .002, or .0025 inhalation doses of a commonly used anesthetic , sevoflurane, or placebo. All volunteers were then shown a series of slides, some with neutral content, such as a cup of coffee, but others were gory, such as a bleeding severed human hand. The following week all volunteers were given PET scans that measured activity in various areas of the brain, while they revisited the same slides. The theory was that the brains would show heightened activity with a second encounter with the horrifying images, a behavior observed in other studies of emotional memory formation. At   concentrations of sevoflurane  lower than .0025, the heightened level of activity was detected as predicted. The scans indicated that brain was  primed to remember quickly,  and particularly energized by the image of the hand. But at .0025 levels, the brain acted as if it had never “seen” the image before. The scientists suggested that this particular anesthetic works to eliminate emotional memory by suppressing the amygdale-to-hippocampus processing route.  Such knowledge might be enable comparison testing of anesthetics when there seems to be high risk of dreaming or awareness with recall, because it shows how recall can be successfully eliminated.

For some reason, surgeries that occur during nighttime seem to  result in both increased reports of dreaming and in verifiable anesthesia with awareness, and some authors have suggested that the natural predisposition to dream at nighttime would provide the best explanation. But this  causative relationship is undercut by the fact that most patients who report verifiable awareness during daytime surgeries also report having dreamed as well. One study noted that they report the awareness first, and subsequently the dream, suggesting that the patients are making a conscious, if  surprisingly not a generally angry effort, to make this factual experience of awareness known as soon as possible.  They consider the dream a separate event that does not explain away the awareness.

The best estimates for periods of actual awareness to occur are the beginning and towards the end of the operation. Surprisingly few patients report actually feeling acute pain during incisions and other procedures that would be expected to evoke pain potentials. They tend, rather, to feel a general sense of pressure being applied.

In   very, very few cases ( less than one tenth of one percent)  of surgeries performed under general anesthesia, the recall with awareness seems to generate emotional disturbance of a severe, PTSD nature, and professional psychotherapy is recommended. Curiously, the most resilient among these cases are children, who seem to get over it more quickly and completely.

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Tony Stankus tstankus@uark.edu Life Sciences Librarian & Professor, University of Arkansas Libraries MULN 233 E, 365 North McIlroy Avenue, Fayetteville, AR 72701-4002, Voice: 479-409-0021; Fax 479-575-4592