NITROUS oxide has long been known to be an impotent and unpredictable human anesthetic.1 In this issue of the journal, Chen et al.1 report that nitrous oxide in clinical use is a potent and predictable human genotoxin. The authors observe that maintenance of anesthesia with 70% nitrous oxide and sevoflurane in patients undergoing colorectal surgery doubles the incidence of DNA damage assessed by the in vitro alkaline single cell gel electrophoresis {i.e., "SCGE" or "comet") assay compared or 80% oxygen and sevoflurane. Genotox-icity using the comet assay has been previously reported with chronic occupational exposure to low concentrations of nitrous oxide, after isoflurane anesthesia with and without nitrous oxide, and after sevoflurane anesthesia without nitrous oxide.
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