Methemoglobinemia due to nitric oxide therapy in a child after cardiac surgery.

A 5-month-old boy with trisomy 21 had repair of ventricular septal defect, atrial septal defect, and ligation of a patent ductus arteriosus. Due to severe pulmonary hypertension, NO inhalation was instituted postoperatively. Over the course of next few hours, he developed life-threatening methemoglobinemia.