The purpose of our study was to determine if premature (≤36 wks) neonates differed from term neonates in their response to inhaled nitric oxide. Methods: We studied 46 infants with hypoxic respiratory failure (OI>0.15). Parental consent was obtained and our protocol was approved by our IRB. Patients were started on 10 ppm iNO and this dose was increased by 10 ppm until a response (PaO2 increased by 10 torr) was seen or we reached a dose of 40 ppm. The dose was increased every 20-40 minutes. Results: Fifteen (88%) of the 17 premature infants had an improvement in oxygenation; 26/29 (90%) term infants responded with improved oxygenation. Survival in premature infants was worse than in term neonates(53% vs 95%, p= 0.02). The dose response curves and changes in oxygenation with time were the same for premature and term neonates. There were no dose response differences between 10, 20 and 30 ppm for either group of infants. In the 12 patients treated with doses > 40 ppm there was no additional improvement in oxygenation at higher doses. Of the 5 patients in whom iNO had no effect, 3(60%) died. In contrast, only 7 (18%) of the 40 responders died.(p=0.06). Conclusion: The dose-response curve for iNO in premature neonates is similar to that of term neonates and failure to show a response is associated with a poor prognosis. Table

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