Impaired vitamin B12 metabolic status in healthcare workers occupationally exposed to nitrous oxide

Abstract

Background. Previous studies demonstrated inactivation of vitamin B12 by nitrous oxide (N2O). The intraoperative exposure to N2O was shown to induce megaloblastic anaemia and myelopathy in subjects with subclinical vitamin B12 deficiency. In contrast, no data concerning the influence of occupational exposure to N2O on vitamin B12 metabolic status are available to date. In the present study, the vitamin B12 status in operating theatre personnel was assessed in relation to the extent of exposure. Methods. Ninety-five operating theatre nurses with the history of exposure to N2O and 90 unexposed counterparts were examined. Vitamin B12 and folic acid were measured by immunoassay. Total homocysteine (tHcy), an indicator of impaired vitamin B12 metabolism, was determined by high performance liquid chromatography. N2O concentration was monitored by adsorption gas chromatography and mass spectrometry. Results. No significant differences were found between both groups with respect to haematological parameters and folic acid. However, subjects exposed to N2O presented with lower vitamin B12 [372.8 (12.1) vs 436.8 (13.2) pmol litre-1, P<0.001] and higher tHcy [11.2 (0.5) vs 8.9 (0.5) μmol litre-1, P=0.006]. The changes in vitamin B12 status were aggravated in subjects exposed to N 2O in concentrations substantially exceeding occupational exposure limit (180 mg m-3) [vitamin B12: 341.9 (17.7) vs 436.8 (13.2) pmol litre-1, P=0.006; tHcy: 12.9 (0.7) vs 8.9 (0.5) μmol litre -1, P=0.047]. Conclusions. Exposure to N2O in healthcare workers is associated with alterations of vitamin B12 metabolic status, the extent of which depends on the level of exposure. © The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved.