The effects of nitrous oxide on plasma homocysteine, vitamin B12 and folic acid levels and evaluation of possible risk factors inpatient undergoing major surgery.

The objectives of this randomized controlled trial were to examine the effects of nitrous oxide, preoperative folate, vitamin B12 status and the other risk factors on plasma homocysteine levels and to assess whether these variables correlate with postoperative complications in patients undergoing major surgery. Therefore, contributing to choose the proper anesthetic technique and prevent possible postoperative complications was aimed.250 volunteered-patients, aged between 30-70 yr, were randomly included into the study. 23 patients, those who had longer or shorter duration of anesthesia than expected, were excluded from the study and the data of the remaining 227 patients were evaluated statistically.In both groups of patients, demographic characteristics, nutritional status and history of concomitant illness were recorded in a questionnaire before the operation.While the nitrous oxide-free group (n=125) received 33% oxygen with 67% air, 33% oxygen with 67% nitrous oxide mixture was administered to patients assigned to nitrous oxide-based anesthesia (n = 125). In both groups, the induction of anesthesia was performed with propofol 2 mg/kg, rocuronium 0.6 mg/kg and fentanyl 0.1 mg/kg and anesthesia was maintained with sevoflurane.On the day of surgery, before the induction of anesthesia, venous blood sample was taken from each of the study participants and plasma vitamin B12, folate and homocysteine concentrations were measured. Patients were screened for a predetermined set of postoperative complications occuring in the first 24 postoperative hours. Also, on the 24th postoperative hour, blood samples were obtained in order to analyze homocysteine levels. Blood samples were transported at 2-4OC. Plasma was immediately seperated and assays were performed at Celal Bayar University Hospital Biochemistry Laboratory.The nitrous oxide group had a significantly increased plasma homocysteine concentration when compared with the nitrous oxide-free group. However, despite the increase in homocysteine levels, we did not observe any major complication due to hyperhomocysteinemia.In the present study, male gender and advanced age were also observed to be the predisposing factors of plasma homocysteine concentration elevations.As shown by other studies, we found that there is a negative correlation between homocysteine and vitamin B12 concentrations.We also assessed that, while dietary intake of milk is associated with plasma vitamin B12 and homocysteine levels, dietary intake of vegetables or fruits is related with folate concentrations.In conclusion, the present study suggests that nitrous oxide is related with elevated homocysteine levels, however, more studies, performed in a broad and different range of risk groups, are required to evaluate the claims about hyperhomocysteinemia causing postoperative complications. Nevertheless, preoperative vitamin B12 and folate concentration assays may have beneficial effects on prevention of possible complications.