Nitrous oxide in blood and urine of operating theatre personnel and the general population

Nitrous oxide (N-2O) was assayed in 676 urine samples and 101 blood samples provided after exposure by operating theatre personnel from nine hospitals. The blood and urine assays were repeated in 25 subjects 18 h after the end of exposure. For 80 subjects, environmental N-2O was also measured during intraoperative exposure. Mean urinary N-2O in the 676 subjects at the end of exposure was 40 mu-g/l (range 1-3805 mu-g/l); in 10 of the 676 subjects, urinary N-2O was in the range 279-3805 mu-g/l (mean 1202 mu-g/l). The 98th percentile was 120 mu-g/l. Mean blood N-2O at the end of exposure, measured in 101 subjects, was 21 mu-g/l (median 16 mu-g/l, range 1-75 mu-g/L). Blood and urine N-2O (1.5 mu-g/l and 4.9 mu-g/l, respectively) in 25 subjects, 18 h after exposure, was significantly higher than in occupationally non-exposed subjects (blood 0.91 mu-g/l, urine 1 mu-g/l). Environmental exposure was significantly related to blood and urinary N-2O (r = 0.59 and r = 0.64, respectively). Blood and urinary N-2O were significantly related to each other (r = 0.71), and were equivalent to about 25% of the environmental exposure level. The mean urinary N-2O of 1202 mu-g/l in 10/676 subjects was not related to environmental exposure in the operating theatre. The highest urinary N-2O levels measured in these 10/676 subjects could be explained by an asymptomatic urinary infection.