Urinary N2O as a measure of biologic exposure to nitrous oxide anaesthetic contamination

Occupational exposure of midwives to nitrous oxide on delivery suites

AIMS

To compare environmental and biological monitoring of midwives for nitrous oxide in a delivery suite environment.

METHODS

Environmental samples were taken over a period of four hours using passive diffusion tubes. Urine measurements were taken at the start of the shift and after four hours.

RESULTS

Environmental levels exceeded the legal occupational exposure standards for nitrous oxide (100 ppm over an 8 hour time weighted average) in 35 of 46 midwife shifts monitored. There was a high correlation between personal environmental concentrations and biological uptake of nitrous oxide for those midwives with no body burden of nitrous oxide at the start of a shift, but not for others.

CONCLUSIONS

Greater engineering control measures are needed to reduce daily exposure to midwives to below the occupational exposure standard. Further investigation of the toxicokinetics of nitrous oxide is needed.

Solid-phase microextraction gas chromatographic-mass spectrometric method for the determination of inhalation anesthetics in urine

Solid-phase microextraction (SPME) has been applied to the headspace sampling of inhalation anesthetics (i.e. nitrous oxide, isoflurane and halothane) in human urine. Analysis was carried out by gas chromatography-mass spectrometry using a capillary column with a divinylbenzene porous polymeric stationary phase. A SPME divinylbenzene-Carboxen-polydimethylsiloxane coated fiber, 2 cm long, was used, and its performances were compared with those of a Carboxen-PDMS in terms of sensitivity, extraction efficiency, extraction time, fiber coating-urine distribution coefficient. For both fibers, linearity was established over four orders of magnitude, limits of detection were below 100 ng/l for nitrous oxide and below 30 ng/l for halogenated. Precision calculated as %RSD was within 3-13% for all intra- and inter-day determinations. The method was applied to the quantitative analysis of anesthetics in the urine of occupationally exposed people (operating room personnel).

Interferences of urinary tract infection in the measurement of urinary nitrous oxide

OBJECTIVES

To investigate the effective role of micro-organisms in producing N2O.

METHODS

The N2O in either urine samples inoculated with 24 microbial strains or urine samples from patients with urinary tract infections were measured.

RESULTS

Gram negative bacilli generally produced high amounts of nitrous oxide (N2O), whereas Gram positive cocci and yeasts did not. The production of N2O depends on the incubation time and follows exponential kinetics, reaching a plateau at 48 hours. Furthermore, the results of urinocultures agreed well with N2O concentrations found in urine samples: samples negative for bacteria were found to contain very low concentrations of N2O whereas those positive--for example, for Enterobacteriaceae--gave highest N2O values.

CONCLUSION

The urinary tract infections caused by Gram negative bacilli are important confounding factors in biological monitoring practices of exposure to inhalation anaesthetics. The current methods adopted to avoid these factors (urine acidification, storage of samples at 4 degrees C) are not good enough because of the relative acid tolerance of some strains and the production of N2O directly into the bladder.

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.

Anesthetic in urine as biological index of exposure in operating-room personnel

The aim of this study was to determine if a relationship existed between some inhalation anesthetics airborne exposure levels (Cl) and the concentration of anesthetics in samples of urine produced throughout the exposure time (Cu). The concentrations of nitrous oxide (N2O), halothane (fluothane), enflurane (ethrane), and isoflurane (forane) in the ambient atmosphere were determined in 190 operating theaters of 41 hospitals in Italy. Nitrous oxide, halothane, enflurane and isoflurane were detected in the urine of 1521 exposed subjects (anesthetists, surgeons, and nurses). The environmental measurements were performed using personal passive samplers, and the biological measurements were performed using the head space method. Significant correlations were found between the anesthetics concentration in urine produced during the shift collected after a 4-h exposure (Cu, microgram/L) and anesthetics environmental concentration (Cl, ppm). The results show that the urinary anesthetic concentration can be used as an appropriate biological exposure index. The biological values (urinary concentration values) proposed are the following: nitrous oxide, 25 micrograms/L, for an environmental value of 50 ppm; halothane, 97 micrograms/L, corresponding to 50 ppm of environmental exposure; 6.2 micrograms/L, corresponding to 2 ppm of environmental exposure; enflurane, 145 micrograms/L for an environmental exposure of 75 ppm and 5.6 micrograms/L for an environmental exposure of 2 ppm; isoflurane, 5.3 micrograms/L for an environmental exposure of 2 ppm. The values proposed are the respectively 95% lower confidence limit and therefore should be considered as a protection for the individual, especially if each biological value is corrected according to analytical variability of the measurements. In our opinion, the method of choice in the assessment of occupational exposure to inhalation anesthetics is the measurement of the urinary anesthetic concentration.

Biological monitoring of occupational exposure to enflurane (ethrane) in operating room personnel

Biological monitoring of occupational exposure to enflurane (ethrane) can be achieved by measuring concentrations of inorganic fluorides in the blood and urine and of enflurane in alveolar air and venous blood. Measurement of these concentrations, however, has limitations. Another method for monitoring exposure to enflurane is to measure its concentration in urine throughout the period of exposure. In this study, we measured the environmental and urinary concentrations of enflurane. Enflurane in the ambient atmosphere was determined in 18 operating theaters of eight hospitals in Italy. Ambient air concentrations exceeded the National Institute for Occupational Safety and Health-recommended time-weighted average exposure level of 1 ppm (median: 1.31 ppm). Enflurane was detected in urine of 159 exposed subjects (anesthetists, surgeons, and nurses). A significant correlation was found between enflurane concentration in urine produced during the shift and environmental concentration (r = 0.77, p = .0001). The results showed that urinary enflurane concentration can be used as an appropriate biological exposure index. The biological values proposed are 153 micrograms/l, corresponding to 75 ppm of environmental exposure; 22 micrograms/l, corresponding to 10 ppm of environmental exposure; and 3.5 micrograms/l, corresponding to 1 ppm of environmental exposure. The proposed values can be regarded as time-weighted average samples, reflecting exposure for a 4-h period.

Urinary excretion of unmetabolized benzene as an indicator of benzene exposure

Benzene concentrations in urine samples (Cu, ng/L) from 110 workers exposed to benzene in chemical plants and gasoline pumps were determined by injecting urine supernate into a gas chromatograph. The urine was saturated with anhydrous N2SO4 to facilitate the passage of benzene in the air over the urine. The solvent was stripped from the urine surface and concentrated on an adsorbent substrate (Carbotrap tube) by means of a suction pump (flow rate 150 ml/m). Wash-up of the head space was achieved by simultaneous intake of filtered air through charcoal. Benzene was thermically desorbed and injected in a column (thermal tube disorder, Supelco; 370 degrees C thermal flash; borosilicate capillary glass column SPB-1, 60 m length, 0.75 mm ID, 1 microns film thickness; GC Dani 8580-FID). Benzene concentrations in the urine from 40 non-exposed subjects (20 smokers > 20 cigarette/d and 20 nonsmokers) were also determined [median value of 790 ng/L (10.17 nmol/L) and 131 ng/L (1.70 nmol/L), respectively]. The 8-h time-weighted exposure intensity (Cl, micrograms/m3) of individual workers was monitored by means of charcoal tubes. The median value for exposure to benzene was 736 micrograms/m3 (9.42 mumol/m3) [geometric standard deviation (GSD) = 2.99; range 64 micrograms/m3 (0.82 mumol/m3) to 13,387 micrograms/m3) (171.30 mumol/m3)]. The following linear correlation was found between benzene concentrations in urine (Cu, ng/L) and benzene concentrations in the breathing zone (Cl, micrograms/m3): log(Cu) = 0.645 x log(Cl) + 1.399 r = .559, n = 110, p < .0001 With exclusion of workers who smoked from the study, the correlation between air benzene concentration and benzene measured in urine was: log(Cu) = 0.872 x log(Cl) + 0.6 r = .763, n = 63, p < .0001 The study results indicate that the urinary level of benzene is an indicator of occupational exposure to benzene.

Evaluation of exposure to isoflurane (Forane): environmental and biological measurements in operating room personnel

The concentration of isoflurane (Forane) in the ambient atmosphere was determined in 11 operating theaters of 5 hospitals in Italy. The concentration of isoflurane in the ambient air exceeds the recommended time-weighted average exposure levels (median value: 113 mumol/m3). Isoflurane was detected in the urine of 45 exposed subjects (anesthetists, surgeons, and nurses). A significant correlation was found between the isoflurane concentration in urine produced during the shift (Cu' nmol/l) and isoflurane environmental concentration (Cl' mumol/m3) (Cu = 0.243 X Cl + 3.712) (r = .90). The results show that the urinary isoflurane concentration can be used as an appropriate biological exposure index. The authors suggest a biological exposure index of 18 nmol/l (3.4 micrograms/l). This is the biological value obtained after 4 h of an average environmental exposure to 81 mumol/m3 (2 ppm).