Awareness during Anesthesia.
By Mohamed Ghoneim. Oxford, Butterworth-Heinemann, 2000. Pages: 208. Price: $59.95.
Awareness during anesthesia is an increasing concern among anesthesiologists. In part, this has been driven by the introduction of the BIS®monitor (Aspect Medical Systems Inc., Natick, MA), which the Food and Drug Administration has cleared for “monitoring the effects of certain anesthetic agents.”*The interest has also been driven by studies in neuropsychology that use clinical anesthesia as a human laboratory to study implicit and explicit memory in a variety of controlled environments.
Awareness during Anesthesia offers the practicing anesthesiologist a useful review of the current status of research in this field. It is divided into nine chapters, all written by well-qualified experts. These chapters include an overview of the research into intraoperative awareness, a review of the available data on both explicit and implicit memory formation during anesthesia, discussions of the utility of auditory evoked potentials and the Aspect BIS®monitor to assess the intraoperative mental state, a review of studies using the isolated forearm technique, and interesting assessments of the emotional and legal consequences of intraoperative awareness.
A few chapters merit special recognition. Ghoneim's chapter, “Implicit memory for events during anesthesia,” is a model review of the scientific literature. Despite a strong personal investment in the field, Professor Ghoneim brings critical appraisal and welcome skepticism to his review of more than 200 studies in the area of awareness, recall, and memory during sedation and anesthesia. He finds common shortcomings in study design, execution, and data analysis. This chapter should be mandatory reading for anyone designing clinical trials that explore awareness and memory during anesthesia. Given the strong case for solid scientific research, I was surprised that the chapter failed to lament the lack of randomized, double-blinded trials in this area.
Other chapters also were also commendable. The chapter by Russell, “Memory when the state of consciousness is known: studies of anesthesia with the isolated forearm technique,” convinced me that I should try the isolated forearm technique in the operating room. The chapter by Wang, “The psychological consequences of explicit and implicit memories of events during surgery,” presents a compelling argument that intraoperative awareness can lead to long-term emotional sequelae. The final chapter, “Medicolegal consequences of awareness during anesthesia,” by Domino and Aitkenhead, offers useful statistics on the incidence of awareness in malpractice litigation and a thoughtful review of the various mistakes in anesthetic technique that are likely to lead to inadequate drug delivery and intraoperative awareness.
The highlight of the book was the chapter by Thornton and Sharpe, “The auditory evoked responses and memory during anesthesia.” First, these authors are engaging writers—I was in hysterics by the second page. Their summaries of the available data were succinct, well-organized, and thoughtfully presented. Their linkage of auditory evoked potentials to brain function was logical and compelling. Last, their final conclusion was clear:“based on currently available evidence we remain convinced that memory formation does not occur in anesthetized (unconscious) patients, and therefore it is unlikely that an unconscious patient will have memory for stimuli presented during unconsciousness.” Earlier chapters had presented conflicting study results that left me, a nonexpert in this field, unable to form any conclusion as to whether my overdosed patients were listening to intraoperative banter.
The textbook is not without its flaws. The chapter by Jones and Aggarwal, “Monitoring the depth of anesthesia,” was a polemic about the shortcomings of the Bispectral Index and the virtues of auditory evoked potentials, a technique closely associated with the authors. The chapter by Andrade, “Learning during sedation, anesthesia, and surgery,” was similarly disappointing, representing a splicing of several of the author's published manuscripts. Also surprising was the lack of chapters from neuroscientists. It is unclear whether this is an oversight by the editor or reflects a lack of interest by neuroscientists in the use of the anesthetized state to understand the process of memory formation. Awareness during Anesthesia drags the reader through multiple reviews of the same studies. A future edition would benefit from better integration between chapters and less duplication.
Awareness during Anesthesia will be an invaluable resource to anyone considering research in intraoperative mental status. Practicing clinicians will also find the material interesting. However, they might want to consider Ghoneim's recent review in Anesthesiology, 1which offers a summary of the key clinical conclusions, or his earlier review of the available scientific literature. 2