Postoperative myeloneuropathy: a preventable complication in patients with B12 deficiency.

Two cases of postoperative neurological deterioration following routine neurosurgical procedures are presented. In each instance, the patient was found to have hematological abnormalities present preoperatively consistent with vitamin B12 deficiency and to have undergone general anesthesia involving N2O. This caused inactivation of the remaining marginal stores of B12 with resultant neurological decompensation. The frequent use of N2O in general anesthesia and the significant incidence of B12 deficiency make it imperative that the surgeon be aware of this complication and its easy prevention. The preoperative recognition of B12 deficiency and N2O-induced neurological deterioration in patients with B12 deficiency is reviewed.