A multicenter epidemiological survey of iNO use in preterm infants in China.

Objective: To investigate the use of inhaled nitric oxide (iNO) in hospitalized preterm infants in China over 10 years and its clinical outcomes.

Methods: A total of 616 premature infants who were administered iNO in the Neonatology Departments of 5 Class A tertiary hospitals in China for ten years from January 2013 to December 2022 were included retrospectively. Based on their enrollment periods, the patients were divided into two groups: Group 1 from January 2013 to December 2017 and Group 2 from January 2018 to December 2022, respectively. The perinatal characteristics, short-term clinical outcomes, and mortality rates were compared between these two groups.

Results: The utilization of iNO in preterm infants grew annually over the past10 years; the utilization of iNO in Group 2 infants increased approximately one-fold when compared with Group 1 (1.52% vs. 0.80%, p < .001), and the increase was greater in gestational age (GA) < 34 weeks compared with 34-36 weeks preterm infants. Moreover, the iNO usage in Group 1 infants with GA < 34 weeks increased from 1.14% to 2.46% and 0.60% to 0.99% in 34-36 weeks preterm infants (p < .001) in Group 2, respectively. Apart from a smaller GA (32.9 w vs. 33.5 w, p < .001) and birth weight (BW, 1900 g vs. 2141 g, p < .001), the initial [14 parts per million (ppm) versus 10 ppm, p < .001] and maximum (15 ppm vs. 10 ppm, p < .001) doses of Group 2 were larger; however, their recent clinical outcomes did not improve with increasing iNO utilization (p > .05)as compared to Group 1, respectively. Although the overall iNO preterm mortality rates over the past 10 years were 25.8%, the mortality rates for preterm infants at 34-36 weeks were significantly lower than for preterm infants at GA < 34 weeks (15.4% vs. 33.8%, p < .001). Nonetheless, no improvement in mortality was observed in Group 2 preterm infants with GA < 34 weeks for the past 5 years when compared with Group 1 (32.9% vs. 35.8%, p > .05) infants, and significantly lower mortality rates were noticed in preterm infants with 34-36 weeks (11.2% vs. 22.7%, p < .001). Patients with hypoxic respiratory failure (HRF) or persistent pulmonary hypertension of the newborn (PPHN) iNO preterm infants did not show lower mortality rates with the increase of iNO use rate (p > .05). The overall mortality rates of preterm PPHN infants with iNO were lower than that of HRF (20.2% vs. 36.5%, p < .001), while the mortality rates of Group 2 preterm PPHN infants with iNO significantly lower than that of HRF (17.7% vs 36.0%, p < .001).

Conclusion: The iNO has been extensively used in Chinese preterm infants over the past 10 years, this increase was more significant in preterm infants with GA < 34 weeks. Moreover, preterm infants using iNO have lower GA and BW, larger initial and maximum doses, and more aggressive strategies in the last past 5 years. Although iNO use in preterm infants with GA of 34-36 weeks has significantly reduced mortality, mortality rates and short-term clinical outcomes of iNO in preterm infants <34 weeks of GA has no obvious improvement. Further studies are required to investigate the efficacy and safety of iNO in preterm infants <34 weeks of GA.