Awareness during general anesthesia: concepts and controversies

Unintended awareness with recall is estimated to occur during about 1 in every 750 general anesthetics. Patients experiencing intraoperative awareness may develop symptoms of post-traumatic stress disorder. To understand how awareness during general anesthesia occurs, its risk factors, strategies for prevention, and the potential role of various drugs used during anesthesia, I begin with a brief review of research on how and where anesthetics suppress different central nervous system functions. I critique the major clinical studies on intraoperative awareness, discussing a number of uncertainties arising from limitations in the scientific methods applicable in this setting. Controversies in this topic are due in part to inconsistent and inadequate data on the impact of awareness events on patients, and divergent views about the value of encephalographic monitoring. I also outline strategies for preventing intraoperative awareness and managing cases when they occur.