Investigations into the effect of nitrous oxide anaesthesia on folate metabolism in patients receiving intensive care.

Anaesthesia with nitrous oxide inactivates vitamin B12 and impairs DNA synthesis in bone marrow cells. The secondary development of folate deficiency may prolong the recovery from these abnormalities in some seriously ill patients. This was investigated, using the deoxyuridine (dU) suppression test, in 48 patients admitted to an Intensive Care Unit (ICU). On admission to the ICU, following nitrous oxide anaesthesia, the pattern of correction of the abnormal dU-suppression tests was typical of that seen in vitamin B12 deficiency; 3 days later the pattern had changed to that usually seen in folate deficiency. During the same period the serum folate levels fell to subnormal values. Further evidence for the development of folate deficiency was provided by treatment with physiological amounts of folic acid which accelerated the recovery of the bone marrow abnormalities present after nitrous oxide anaesthesia. Urinary folate excretion was measured by radioassay, and increased following anaesthesia with nitrous oxide, however, this was insufficient by itself to explain the development of folate deficiency.