Human bone marrow biochemical function and megaloblastic hematopoiesis after nitrous oxide anesthesia.

Prolonged exposure to nitrous oxide (N2O) inhibits bone marrow function. The duration of exposure to nitrous oxide necessary to induce these changes and their permanence is unknown. The possible prophylactic effect of prior treatment with folinic acid has not been examined previously. Bone marrow function in patients receiving nitrous oxide was assessed by the deoxyuridine (dU) suppression test. Morphologic changes in the bone marrow were also studied. One group was exposed for under 6 h, the next for between 12 and 24 h and a control group who received nonitrous oxide. The control group and the short exposure group showed no abnormality of bone marrow function. The long exposure group had abnormal dU supression tests and a megaloblastic hematopoiesis. The changes observed in this group resolved 12 h after discontinuance of the anesthetic. The changes observed could be prevented by the preoperative administration of folinic acid. The absence of either morphologic or dU suppression test abnormalities following N2O anesthesia for periods of less than 6 h confirms the safety of this anesthetic for the majority of operations for which it is used. It has been confirmed that prolonged exposure to the gas causes impaired marrow function which is of a temporary nature and may be prevented by the prior administration of folinic acid.