Publish date: 13 January 2021

Around 1 in 250 women may experience accidental awareness during pregnancy-related surgery – including caesarean section – under general anaesthesia, and some may experience long-term psychological harm, according to a study involving 72 hospitals led by UCLH.

The study sheds light on why this awareness may occur – finding an association with certain anaesthetic drugs (thiopentone) and muscle relaxants. Emergency operations late at night were also associated with awareness.

Researchers said the work demonstrates the need for evidence-based guidelines in this area. The Obstetric Anaesthetists' Association in conjunction with the Association of Anaesthetists have already started this work.

It is anticipated that the results of this project will lead to changes in the practice of individual anaesthetists, their training and hospital support systems both nationally and internationally.

While accidental awareness is rare, women with concerns about the issue are advised to contact their obstetric centre for information and support.

Accidental awareness occurs when a patient is temporarily conscious during a general anaesthetic and can remember things that happened during surgery, perhaps feeling pain or being unable to move. More commonly however, awareness occurs during the transition at the very start and end of a general anaesthetic (i.e. before and after surgery), as the patient is going to sleep or waking up. Although accidental awareness during general anaesthesia is rare, and the experiences usually only lasted for a few seconds or minutes, the complication remains an important concern for both patients and anaesthetists.

The study, published in Anaesthesia (a journal of the Association of Anaesthetists), found that 1 in 256 women undergoing pregnancy-related surgery, including caesarean section, under general anaesthesia experienced awareness – a figure much higher than reported before. A recent national audit into accidental awareness (NAP5) indicated that approximately 1 in every 19,000 patients undergoing general anaesthesia spontaneously reported accidental awareness to medical staff.

This new research was driven by the suggestion from NAP5 that women having caesarean section, or other surgery at childbirth, may have a higher incidence of awareness. The researchers studied over 3,000 women having general anaesthesia for obstetric procedures in 72 NHS hospitals in England and found 12 reports of awareness: seven (58%) of patients were distressed and five (42%) felt paralysed (that they were unable to move, which may occur due to the common use of drugs to relax muscles during general anaesthesia for pregnant women). Two women (17%) felt paralysis with pain. Other sensations included tugging, stitching, feelings of dissociation and being unable to breath. Longer term psychological harm often included features of post-traumatic stress disorder.

Factors associated with accidental awareness during general anaesthesia were high (overweight) body mass index (BMI) (25–30 kg/m2); low (underweight) BMI (<18.5 kg/m2); out-of-hours surgery; and use of ketamine or thiopental for induction.

The authors said there could be other factors contributing to the cases of awareness, noting that childbirth is a time of heightened attention to surrounding events, meaning brief episodes of awareness may be magnified in recall, as are other details of the birthing experience. Another possibility is that the hormonal changes associated with pregnancy influence memory, recall or event sensitivity to general anaesthesia and increase the likelihood of awareness.

Dr Peter Odor, Project Lead and Consultant Anaesthetist at University College Hospital in London, explained: “This research is patient-focussed throughout. We identified a complex range of risk factors for awareness, including drug types and organisational variables. Although the incidence of awareness during caesarean section is much higher than that in the general surgical population, it is important to emphasise that general anaesthesia remains safe and around half the patients that experienced awareness did not find it distressing. Although we have provided many answers, questions remain as to exactly why awareness is more common in pregnant women; our next steps are to apply the lessons learned from this study to help reduce risk in the future.”

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