Odor, Peter Mark; (2023) Accidental awareness during general anaesthesia in obstetric surgery. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Accidental awareness during general anaesthesia (AAGA) occurs when a patient becomes unintentionally conscious during general anaesthesia, which may involve unpleasant memories of experiences during surgery. Contributory factors that may increase risk of AAGA coincide in pregnant women undergoing general anaesthesia for childbirth related surgery. Whilst obstetric general anaesthesia has largely been substituted by spinal and epidural (termed neuraxial) anaesthetic techniques, in which a mother can be awake and pain free during childbirth, general anaesthesia is still necessary to facilitate surgery rapidly in emergency situations or for mothers with certain medical conditions. In this thesis I investigate the distinct characteristics of general anaesthesia for pregnant women undergoing surgery for childbirth, whether these characteristics increase risk of AAGA, and changes to obstetric anaesthetic technique occurring in the context of wider anaesthetic developments over time. I provide evidence on the incidence, experiences, risk factors and psychological consequences of AAGA in peripartum women. Challenges to large scale clinical study of AAGA are explored and addressed in the design of a multi-centre, prospective, cross-sectional cohort study of women receiving general anaesthesia for obstetric surgery in 72 hospitals in England. A four-stage process for screening patients using direct questioning, verifying with corroborative detail, adjudicating and classifying descriptions of experiences is described. The interactional nature of research interviews, statistical modelling, psychological factors and the neurophysiology of memory are considered during development of study methodology. Psychological morbidity was assessed for 12 months after surgery. As part of an embedded study, descriptive epidemiology of obstetric patients and general anaesthesia techniques were identified, alongside risk factors for airway complications. A total of 3,115 patients were recruited, 12 of whom had certain/probable or possible AAGA: a prevalence of 0.39% or 1 in 256 (95%CI 149–500) for all obstetric surgery. Distressing experiences were reported by seven (0.22%) patients, paralysis by five (0.16%) and paralysis with pain by two (0.06%). Associations were identified between AAGA and patient risk factors (abnormal body mass index), organisational factors (out-of-hours surgery) and pharmacological factors (use of thiopental during induction of anaesthesia). Contextual factors relating anaesthesia for obstetric patients with AAGA and other anaesthesia complications, including difficult airway management, were evaluated. My study methodology and it’s context, in English public sector hospitals, identified a higher risk of AAGA in obstetric patients than previously detected using other methods and locations. These results have implications for healthcare policy of obstetric anaesthesia, informed consent of patients receiving general anaesthesia and post-natal screening care. I conclude on recommendations to minimise awareness risk for future patients and address the challenge of implementing systemic improvements in obstetric general anaesthesia care and patient safety.

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