MEGALOBLASTIC HÆMOPOIESIS IN PATIENTS RECEIVING NITROUS OXIDE

Abstract

In a prospective study the incidence of megaloblastic change after ventilation with nitrous oxide for periods of up to 24 h has been determined and the cause of the altered D.N.A. synthesis studied with the deoxyuridine (dU) suppression test in 22 patients undergoing cardiac bypass surgery. 8 patients who received nitrous oxide and oxygen for 24 h had megaloblastic bone-marrow aspirates and abnormal dU suppression tests at the end of ventilation. 5 patients who received no nitrous oxide had normoblastic aspirates and normal dU suppression tests. Of the remaining 9 patients, who received nitrous oxide during the operation only, 3 had abnormal dU suppression tests at 24 h. The abnormality revealed by the dU suppression tests was identical with that found in vitamin-B 12 deficiency, but the patients' serum-B 12 concentrations were normal. These results suggest that nitrous oxide interferes with the function of vitamin B 12. Nitrous oxide oxidises vitamin B 12 in vitro, and probably also in vivo when premixed 50% nitrous oxide and 50% oxygen mixture ('Entonox') is given.