General anesthetics: neuroprotective or neurotoxic?

ABSTRACT

Many historical general anesthetics have been waxed and waned in the market of anesthetic field, mostly due to organ toxicities related to their metabolism, active metabolites and biodegradation, or other reasons. Modern anesthetics available now are known to undergo metabolism to the extent of clinical insignificance compared with the old ones. However, animal studies provided extensive evidences showing that general anesthetics are neurotoxic or neuroprotective in certain circumstances along with the advancement of knowledge on simultaneous neural injury and healing processes. Until now, there have been few prospective randomized clinical trials conducted to reveal these two issues. In fact, the concerns of the long-term effect of anesthetics on cognitive and behavior decline seem to be in arrears compared with those of the immediate effect of anesthetics, such as the rapidity of onset/offset of action, intraoperative hemodynamic controls or postoperative nausea and vomiting, etc. At present, we anesthesiologists, are challenged with the rapidly changing environments, in which the elderly population grows or a variety of sedation depth are required especially for patients of extreme ages. Concerns on anesthetics' effects with double edged sword are mounting from basic scientists and/or anesthesiologists, as well as public society, such as FDA in US. Therefore, I review the current findings from animal and human researches regarding the anesthetic potentials for neuroprotection and/or neurotoxicity under certain circumstances and their links with findings of clinical researches.