Methemoglobinemia, nitric oxide

Nitric oxide oxidizes hemoglobin to methemoglobin, two-thirds of which is reduced by nicotinamide adenine dinu-cleotide (NAD) methemoglobin reductase (1). Several ethnic groups, such as native Americans, have NAD methemoglobin reductase deficiency. There have been reports of methemoglobinemia after accidental overdosage of inhaled nitric oxide in native Americans and others (1). 

There may also be partial deficiency of methemoglobin reductase in neonates (1). In the Neonatal Inhaled Nitric Oxide Study the dose of inhaled nitric oxide had to be reduced in 11 of 114 patients (9.6%) because of raised methemoglobin. At doses of 1.25-80 ppm, methemoglobinemia is uncommon in one study only three of 471 (0.6%) patients discontinued therapy for this reason (17). 

A 7-month-old girl was ventilated with inhaled nitric oxide 40 ppm and developed methemoglobinemia after the application of Emla to an 8 cm area of skin for 5 hours (17). Shortly after removal she developed cyanosis, with a methemoglobin concentration of 16%, which resolved with two doses of methylthioninium chloride. 

Sinisterra S, Miravet E, Alfonso 1, Soliz A, Papazian O. Methemoglobinemia in an infant receiving nitric oxide after the use of eutectic mixture of local anesthetic. J Pediatr 2002 141(2) 285-6. 

D. Inhaled nitric oxide (eg, used tor therapeutic purposes as a pulmonary vasodilator in neonates) can have extrapulmonary effects, including reduced platelet aggregation, methemoglobinemia, and systemic vasodilation. 

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