The hematological effects of nitrous oxide anesthesia in pediatric patients

BACKGROUND: Prolonged administration of nitrous oxide causes an increase in plasma homocysteine in children via vitamin B₁₂ inactivation. However, it is unclear whether nitrous oxide doses used in clinical practice cause adverse hematological effects in pediatric patients. METHODS: This retrospective study included 54 pediatric patients undergoing elective spinal surgery: 41 received nitrous oxide throughout anesthesia (maintenance group), 9 received nitrous oxide for induction and/or emergence (induction/emergence group), and 4 did not receive nitrous oxide (nitrous oxide-free group). Complete blood counts obtained before and up to 4 days after surgery were assessed for anemia, macrocytosis/microcytosis, anisocytosis, hyperchromatosis/hypochromatosis, thrombocytopenia, and leukopenia. The change (Δ) from preoperative to the highest postoperative value was calculated for mean corpuscular volume (MCV) and red cell distribution width (RDW). RESULTS: No pancytopenia was present in any patient after surgery. All patients had postoperative anemia, and none had macrocytosis. Postoperative MCV (mean [99% confidence interval]) peaked at 86 fL (85-88 fL), 85 fL (81-89 fL), and 88 fL (80-96 fL) and postoperative RDW at 13.2% (12.8-13.5%), 13.3% (12.7-13.8%), and 13.0% (11.4-14.6%) for the maintenance group, the induction/emergence group, and the nitrous oxide-free group. Two patients in the maintenance group (5%) developed anisocytosis (RDW >14.6%), but none in the induction/emergence group or in the nitrous oxide-free group (P = 0.43). Both ΔMCV (P = 0.52) and ΔRDW (P = 0.16) were similar across all groups. CONCLUSIONS: Nitrous oxide exposure for up to 8 hours is not associated with megaloblastic anemia in pediatric patients undergoing major spinal surgery.