Studies on the haemopoietic toxicity of nitrous oxide in man

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Abstract
N2O inactivates vitamin B12 and in man can produce a megaloblastic anemia. Hematological and biochemical changes were studied in 9 surgical patients ventilated with 70% N2O for up to 24 h and in 3 control patients. There was a rise in the numbers of hypersegmented neutrophils in peripheral blood following N2O. Serial bone marrow aspirates showed gross megaloblastic change after 24 h of N2O which had reverted to normoblastic but dyserythropoietic hemopoiesis by 1 wk. Giant forms of early myeloid precursors were also seen after 24 h ventilation with N2O but by 1 wk abnormalities were evident in more mature cells, metamyelocytes and segmented neutrophils. Megaloblastosis was associated with abnormal dU [deoxyuridine ] suppression which showed a correction pattern similar to that seen in vitamin B12 deficiency. Administration of N2O was also associated with a progressive rise in serum folate and fall in serum Met levels. No similar patterns were seen in the 3 control patients.