Vitamins in Nitrous Oxide Study

Background and significance: Recent studies have shown that nitrous oxide (N2O) anesthesia may be associated with an increased risk of adverse cardiovascular outcomes. It is well-known that N2O inhibits vitamin B12-dependent enzymes and as a result increases plasma homocysteine concentrations. Homocysteine has been identified as risk factor for cardiovascular disease. Therefore elevations in homocysteine after N2O may be a causative factor in N2O toxicity. In a previous investigation, we found that patients who carry a homozygous mutation in the MTHFR gene develop higher homocysteine levels after N2O anesthesia than non-carriers. These patients might be at higher risk for adverse cardiac outcomes from N2O. Thus, there may be a pharmacogenetic mechanism to account for the adverse cardiac outcomes from N2O. Moreover, prevention of N2O-increased homocysteine concentrations in these high risk patients by perioperative vitamin B12 and folate supplementation might decrease the incidence of adverse cardiac outcomes.

Hypothesis: Patients carrying a homozygous MTHFR 677C>T or 1298 A>C variant allele will have a higher incidence rate of postoperative myocardial ischemia after N2O anesthesia [detected by serial TnI measurements] due to elevated homocysteine levels than normal "wild-type" non-carriers, and that the incidence rate will be reduced if they receive perioperative vitamin B12/folate supplementation.

Primary outcome: Myocardial ischemia in the first 72 hours after surgery (measured by serial troponin and ECGs).

Secondary outcome: Composite endpoint of 30-day mortality and major cardiac morbidity (non-fatal MI)

Design: Randomized controlled trial. 500 patients will receive N2O during surgery and will be randomized to receive B-vitamins or placebo. 125 patients will receive no N2O and no B-vitamins (control arm). Mendelian randomization of MTHFR genotype.

Intervention: IV vitamin B12 (1 mg) and folate (5 mg) pre- and postoperatively

Study setting: Barnes-Jewish-Hospital, St. Louis, MO

Patients: Patients scheduled for major surgery with or at risk for coronary artery disease

Inclusion criteria

• Adult patients; age >18 yrs, ASA III-IV
• Previously diagnosed coronary artery disease or at risk for coronary artery disease
• Scheduled for major surgery (>2 hrs)

Exclusion criteria

• Patients not expected to live past 24 hours (ASA 5)
• Patients with significant pulmonary disease requiring supplemental oxygen
• Patients taking supplemental vitamin B12 or folate
• Contraindication against N2O (pneumothorax, mechanical bowel obstruction, middle ear occlusion, laparoscopic surgery, raised intracranial pressure)
• Hypersensitivity to cobalamins
• Leber's disease (hereditary optic nerve atrophy) [vitamin B12 interaction]
• Seizure disorder [folate interference]