Inhaled nitric oxide and methemoglobin in full-term infants with persistent pulmonary hypertension of the newborn.

Inhaled nitric oxide (iNO), a potent pulmonary vasodilator, has become a mainstay therapy for neonates with persistent pulmonary hypertension of the newborn (PPHN). However, it also oxidizes hemoglobin to methemoglobin (metHgb), thereby reducing the delivery of oxygen to tissues. Studies have suggested that elevated levels of metHgb may be avoided by limiting iNO concentration to less than 40 parts per million (ppm). However, the relationship between iNO exposure and elevated levels of metHgb (greater than 4%) has not been examined. Therefore, we studied this relationship in full term newborns with PPHN. We reviewed the charts of twenty-eight neonates with a diagnosis of PPHN admitted to our Intensive Care Nursery between 1/92 and 10/97. Our retrospective analysis demonstrated that: (1) high metHgb levels can occur with exposure to low iNO concentration (three of eight newborns with maximum metHgb levels >4% had been exposed to no more than 40 ppm of iNO concentration); and (2) cumulative iNO ( summation operatoriNO) exposure was the best predictor of elevated metHgb levels (seven of nine newborns receiving summation operatoriNO>2000 ppm x hour had maximum metHgb levels >4%). Copyright 2002 Elsevier Science Ltd.