Andrew Davidson graduated in medicine from The University of Melbourne, Australia. He has trained in anaesthesia in Nottinghamshire, the UK; and Melbourne, Australia. He underwent fellowships in paediatric anaesthesia at Sophie Children’s Hospital, Rotterdam; and Boston Children’s Hospital. He has received a Diploma of Biostatistics and Doctorate of Medicine (MD) from The University of Melbourne.
Dr Davidson is currently Director of Clinical Research for the Royal Children’s Hospital. He is also a Senior Staff Anaesthetist, Department of Anaesthesia & Pain Management, the Royal Children’s Hospital, Director of Anaesthesia Research at the Murdoch Childrens Research Institute and an Associate Professor, Department of Paediatrics, The University of Melbourne.
His clinical interest is paediatric neuroanaesthesia.
He is a Section Editor for the journal Pediatric Anesthesia, a Guest Editor for Anesthesia and Analgesia and an Associate Editor for Anesthesiology.
He has published over 70 peer reviewed papers, 10 book chapters and one book. He has received over 4 million dollars in research grants including four Australian National Health and Medical Research Council project grants. He is the principle investigator for the GAS study, a multi-national RCT examining neurotoxicity of anaesthesia in infants. His anaesthesia research interests are awareness, the EEG and anaesthesia, and neurotoxicity of anaesthesia. As Director of Clinical Research he has particular interests in trial design, the ethics of research in children, promoting clinical research in hospital environments, and the regulatory challenges facing clinical researchers.
Intra-operative awareness: how to prevent it, how to deal with it.
Andrew Davidson
The prevention and management of intra-operative awareness firstly requires a clear definition of the phenomenon. The clearest definition is that awareness is the free recall or explicit memory of events that occurred during anaesthesia at a time when the anaesthetist had intended the patient to be unconscious with no recall. Although this definition seems clear, the measure of awareness is difficult. It is a subjective experience. In some cases awareness clearly occurred while in others there is a risk that memories recalled during the procedure where in fact fragmentary memories in the peri-operative period. Detecting awareness may also be difficult if patients don’t immediately recall the event, or if they are reluctant to report it. Thus the science of awareness prevention is inherently imprecise.
There are two approaches to the science of preventing awareness. The first is to understand the mechanism and the second is to assess prevention strategies in clinical settings: cohort studies or trials.
The commonest cause of awareness is probably due to error or mechanical failure. These causes are well described and prevention can be modelled on preventing common errors. But the mechanism of awareness is not always so straightforward. We still have an incomplete understanding of the mechanisms of consciousness, memory and how anaesthetics actually work. We do have some idea of what dose of anaesthetic is usually needed to produce what most would call “unconsciousness” and to prevent memory formation, but in some cases memory may still form even with what appears to be an adequate dose. Could this be due to genetic reasons?
Our limitations in understanding consciousness, memory and anesthesia mechanisms limit our ability to completely understand why awareness may occur and it also limits our ability to monitor brain function to prevent awareness. Using the EEG is a crude and indirect measure of consciousness. From a mechanistic perspective there are reasons to see why it should work but also lots of reasons to see why it should sometimes fail.
There are now several studies that have looked at prevention strategies in a clinical setting. These studies show that BIS is better than standard of care in high risk groups – especially perhaps when TIVA is used. It has also been shown that aiming for a minimum anesthetic end tidal dose can reduce the risk of awareness. There is debate as to which is most effective, but it seems clear that if the anaesthetist aims for a particular BIS or end tidal concentration then the risk is reduced. Extrapolating these data to other patient populations is difficult. Generalising the results of clinical studies is easier when the mechanisms are understood. As we don’t completely understand mechanisms of awareness or the EEG relationship to consciousness then there will be some reluctance to apply the findings of the larger trials to other patient populations or even to individual patients.
Managing awareness involves asking if it has occurred. Anaesthetists should get into the habit of seeing their patients post op; and while direct asking is not always required they could ask about memories of the whole event or how they felt about the anaesthetic. In cases where awareness was more likely, then more direct questioning may be needed. Unfortunately if a florid awareness event did occur then patients may be reluctant to report this immediately. If awareness is suspected for any reason then the anaesthetist should follow up with a phone call a week or so later. Even then they may not report the event.
Awareness may be associated with distress and psychological disturbance including post traumatic stress disorder. If there is any hint of this, then the patient should be referred for psychological counselling. Unfortunately those at greatest risk of PTSD may be those least likely to report the event or to report any early symptoms. If there is a high risk of awareness and a suspicion of psychological distress then a repeat follow up call is needed.
When talking to patients about awareness the anaesthetist should be empathetic and understanding. Any factors that may have contributed to the event should be explained in full disclosure. The anaesthetist should also discuss the case at quality review meetings to determine if any systematic errors can be identified and corrected.
1. PERSONAL INFORMATIONS
Was born in Cologne / Germany on 18th October 1968.
Dr. Jost Kaufmann is a registered Specialist in Pediatrics and Anesthesiology and employed as Consultant Pediatric Anesthesiologist at one of the biggest pediatric hospitals in germany, the Children´s Hospital in Cologne. The department of pediatric anesthesia performs about 6.500 anesthetic procedures per annum, whereas more than a half of the patients is younger than 2 years and the smallest are less than 500 grams. More than 60 % of the procedures are performed with locoregional anesthesie (alone or in combination with general anesthesia).
Jackie Andrade has been studying memory and awareness in anaesthesia for 20 years and has published around 80 articles, books and chapters, about 30 of which are on anaesthesia. She was trained at the Universities of Cambridge and Manchester, followed by post-doctoral research at the Medical Research Council's Applied Psychology Unit in Cambridge and a lectureship at the University of Sheffield. She is currently Professor of Psychology at Plymouth University.
, DEAA, DESRA is associate professor of anesthesiology at the Academic Medical Center in Amsterdam. He is head of the acute pain service and pediatric anesthesia at the AMC and Lecturer in Anesthesiology at the University of Düsseldorf. His research interest includes regional anesthesia, pain medicine, pediatric anesthesia, neurotoxicity and neuroplasticity.
