Recommended Exposure Limits for Desflurane and Isoflurane

Berry questions whether the National Institute of Occupational Safety and Health (NIOSH)-recommended exposure limits for isoflurane and desflurane are appropriate. This is an issue we addressed in our article [1]. The 2-ppm ceiling for volatile anesthetics was indeed established before isoflurane and desflurane became available [2]; this limit is nonetheless applicable. It is also worth remembering that NIOSH does not consider these maximal acceptable concentrations to be optimal or even demonstrably "safe." Instead, they constitute practically obtainable levels of environmental toxins that NIOSH considers hazardous and for which no safe levels have been defined. These leads to their explicit statement: "NIOSH is unable to identify a safe level of exposure for waste anesthetic gases. Therefore, it recommends that the risk be minimized by reducing exposures to the greatest extent possible." Berry points out that "isoflurane and desflurane have different potencies [and] are metabolized to different compounds" than the anesthetics considered by NIOSH. However, there is no basis for assuming that toxicity scales with potency. It is, in fact, unlikely because anesthetic toxicity is presumably mediated by mechanisms other than the ones that modulate anesthetic action. Of course, the concentrations we observed were fully reported in our article. Readers are thus free to compare these values with whatever exposure limits they might consider appropriate. It is obvious that "future work should be directed toward establishing recommended exposure limits for the volatile anesthetics currently in use." This is especially true because, as Berry concedes, no laboratory studies or epidemiologic surveys have evaluated the toxicity associated with occupational exposure to these commonly used drug. Before embarking on such large and expensive epidemiological investigations, however, it seems reasonable to first evaluate exposure levels in various settings. Our study does so-and identifies nontrivial nitrous oxide, isoflurane, and desflurane concentrations in one postanesthetic care unit. Daniel I. Sessler, MD Department of Anesthesia; University of California-San Francisco; San Francisco, CA 94143 Ludwig Boltzmann Institute for Clinical Anesthesia and Intensive Care; Outcomes Research[trade mark sign] Group; Department of Anesthesia and General Intensive Care; University of Vienna; Vienna, Austria