Long-term effects of nitrous oxide anaesthesia on laboratory and clinical parameters in elderly Omani patients: a randomized double-blind study

Aims: This study examined the long-term effects of nitrous oxide anaesthesi a on serum levels of cobalamin and folate, red cell folate levels and haema tological parameters, and neurological status in elderly Omani patients. Methods: Sixty-nine consecutive patients undergoing ophthalmic surgery were randomly and double-blind assigned to nitrous oxide or propofol anaesthesi a. They met the following entry criteria: age 55 years or above, no major o rgan failure, no clinical signs or symptoms of cobalamin or folate deficien cy, mean cell volume (MCV) less than or equal to 96 fl, haematocrit (Hct) h igher than 0.3 and no cobalamin and/or folate substitution therapy during t he preceding months. Serum levels of cobalamin and folate, red cell folate levels, and haematological parameters were measured prior to anaesthesia an d 3-5 weeks later. At that time, the patients also underwent thorough neuro logical examination. Results: Data of 51 patients were complete and considered for analysis. In both nitrous oxide and propofol group, the range of exposure time was compa rable (+/-1 h). In the nitrous oxide group, a slight but significant decrea se in haemoglobin, Hct, and red blood cell count (RBC) (P < 0.001) was obse rved, whereas there was a mild increase in mean cell haemoglobin (MCH) and mean cell volume (P < 0.05). In addition, there was a significant decrease in serum folate levels (P < 0.05). Hct and RBC decreased slightly in the pr opofol group (P < 0.05), whereas there was a small increase in MCH. There w as no difference between the two anaesthetics with regard to serum cobalami n and red cell folate levels, but there was a significant decrease in serum folate levels in the nitrous oxide group compared to those in the propofol group. Three patients with pre-existing low red cell folate levels, who we re randomized to nitrous oxide anaesthesia, developed clinical symptoms of folate deficiency. Conclusions: This study showed that short-term (40-80 min) nitrous oxide an aesthesia did not affect cobalamin levels but reduced serum folate levels i n this elderly population. Although this reduction was clinically irrelevan t, some patients with pre-existing asymptomatic folate deficiency developed nitrous oxide-induced folate deficiency.