[Clinical evaluation of instantly generated inhaled nitric oxide in the treatment of neonatal pulmonary arterial hypertension].

Objective: To explore the efficacy and safety of instantly generated inhaled nitric oxide (iNO) for treating neonatal pulmonary arterial hypertension (PAH) complicated with severe hypoxic respiratory failure. Methods: This single-center, single-arm, prospective study included 32 neonates with PAH complicated with hypoxic respiratory failure who were hospitalized in the neonatal intensive care unit (NICU) of Beijing Children's Hospital Affiliated to Capital Medical University from March 2023 to March 2025 and received immediate iNO generation therapy. The demographic data, maternal pregnancy, mechanical ventilation parameters, arterial blood gas indexes, other hospitalization data and safety indexes of iNO treatment were collected. The time point for starting iNO treatment was set as 0 h, and the observation time points were 1, 6, 12, 24, 48 h after treatment and when iNO treatment was stopped. The positive reaction of iNO treatment was defined as the decrease of oxygenation index (OI)>10% or the increase of arterial partial pressure of oxygen (PaO₂)>10% after treatment. The OI, mechanical ventilation parameters, arterial blood gas index changes and treatment positive reaction ratio were analyzed to evaluate the effectiveness of iNO treatment, and the nitrogen dioxide concentration, methemoglobin (MetHb) concentration and other indicators were analyzed to evaluate the safety of iNO treatment. Paired t test or Wilcoxon signed rank sum test was used to compare the observation indexes at different treatment times. Friedman test was used to compare the concentration of nitrogen dioxide and MetHb at multiple treatment times. Receiver operating characteristic (ROC) curve was used to analyze the best cut-off value of OI related indexes to distinguish the treatment outcome of iNO. Results: Among 32 neonates, 18 (56%) were males and 14 (44%) were females, the gestational age was 38 (35, 39) weeks, the birth weight was 3.1 (2.3, 3.4) kg, and the age of enrollment was 3 (2, 8) days. The OI and the mean airway pressure at 48 h after treatment were both lower than those at 0 h ((10.4±2.0 vs. 22.6±2.5, 13.0 (12.0, 14.0) vs. 14.0 (13.0, 16.0) cmH₂O, 1 cmH₂O=0.098 kPa, both P<0.05). The fraction of inspired oxygen at 24 and 48 h after treatment were both lower than those at 0 h (both P<0.05). The PaO2 at 6, 12, 24 and 48 h after treatment were all higher than those at 0 h (all P<0.05). The proportion of positive reactions to iNO treatment was 20 neonates (63%), 22 neonates (69%), 23 neonates (72%), 23 neonates (72%) and 26 neonates (8%) at 1, 6, 12, 24, 48 h after treatment, respectively. No occurrence of methemoglobinemia, excessive nitrogen dioxide concentration, or device related adverse events were observed. Out of 32 neonates, a total of 24 neonates (75%) were cured or improved and discharged according to medical advice, while 8 neonates (25%) died in the hospital. The best cut-off value of OI at 0 h and the decline range of OI at 12 h to distinguish the outcome of hospitalization were 24.8 and 22.2%, respectively. Conclusion: It was effective and safe to use instantly generated iNO to treat neonatal PAH with severe hypoxic respiratory failure.