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

Nitrous oxide (N2O) 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 N2O was also measured during intraoperative exposure. Mean urinary N2O in the 676 subjects at the end of exposure was 40 micrograms/l (range 1-3805 micrograms/l); in 10 of the 676 subjects, urinary N2O was in the range 279-3805 micrograms/l (mean 1202 micrograms/l). The 98th percentile was 120 micrograms/l. Mean blood N2O at the end of exposure, measured in 101 subjects, was 21 micrograms/l (median 16 micrograms/l, range 1-75 micrograms/l). Blood and urine N2O (1.5 micrograms/l and 4.9 micrograms/l, respectively) in 25 subjects, 18 h after exposure, was significantly higher than in occupationally non-exposed subjects (blood 0.91 microgram/l, urine 1 microgram/l). Environmental exposure was significantly related to blood and urinary N2O (r = 0.59 and r = 0.64, respectively). Blood and urinary N2O were significantly related to each other (r = 0.71), and were equivalent to about 25% of the environmental exposure level. The mean urinary N2O of 1202 micrograms/l in 10/676 subjects was not related to environmental exposure in the operating theatre. The highest urinary N2O levels measured in these 10/676 subjects could be explained by an asymptomatic urinary infection.