Background: One-third of infants with persistent pulmonary hypertension of the newborn (PPHN) do not respond to inhaled nitric oxide (iNO). If iNO is not delivered to the pulmonary vasculature because of parenchymal lung disease, it cannot interact with hemoglobin to form methemoglobin (MHb). Objective: To study the correlation between oxygenation response to iNO in infants with PPHN secondary to parenchymal lung disease and initial MHb% to cumulative NO exposure (ppm × hours) ratio (MHb/ΣNO). Study Design: Retrospective chart review of neonates with PPHN secondary to parenchymal lung disease treated with iNO comparing non-responders (PaO2/FiO2 ratio<10 change with iNO) with responders (≥10 change). Result: Non-responders (n=16) had a PaO2/FiO2 of 83±48 (mean ± s.d.) and decreased to 74 ± 44 after iNO. PaO2/FiO2 increased from 70 ± 48 to 151 ± 63 with iNO among responders (n=36). The MHb/ΣNO ratio was low (0.024 ± 0.012) among non-responders compared with responders (0.07 ± 0.053, P<0.005). Conclusion: Inadequate oxygenation response to iNO is associated with lower MHb/ΣNO, suggesting suboptimal delivery of iNO to the pulmonary vasculature.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health
- Obstetrics and Gynecology