Abstract 1894

INTRODUCTION INO improves oxygenation and reduces the need for extraccorporeal membrane oxygenation in neonates with hypoxic respiratory failure. One mechanism for INO's effect is enhancement of ventilation-perfusion matching. Last year we reported the decline in arterial oxygen tension (PaO2) associated with weaning INO. Continuing to investigate the effect of weaning INO, we measured the change in pCO2 and pH associated with weaning INO.

METHODS Prospectively collected data from 505 INO weaning attempts on 84 neonates at 9 medical centers. Weaning attempts were made on INO-responsive NINOS patients or similarly treated open label patients. Ventilatory settings and FiO2 were kept constant during the weaning period. Changes in PaO2, pCO2 and pH were determined for INO reductions (80-40, 40-20, 20-10, 10-5, 5-4, 4-3, 3-2, 2-1 ppm weans) and discontinuations (5-0 & 1-0 ppm weans). ANOVA was used to investigate differences between wean types, linear regression was used to investigate for correlations.

RESULTS Discontinuation attempts resulted in greater changes in PaO2, pCO2 and pH (see Table) than reducing INO. There was no correlation between the change in pCO2 or pH during INO weaning with the: change in PaO2, magnitude of INO reduction, or pre-wean respiratory parameters. Patients undergoing INO weaning on conventional ventilation experienced a significantly greater increase in pCO2 than those on high frequency oscillatory ventilation (1.4 ± 4.1 torr vs. 0.5 ± 4.1 torr, p=0.0189), this was not significant for PaO2 (p=0.0938). Surfactant treated patients experienced significantly less decline in PaO2 when weaning INO (-15.9 ± 37.8 torr vs. -28.8 ± 46.5 torr, p=0.0026), this was not significant for pCO2 (p=0.7874).

Table 1 No caption available
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CONCLUSIONS Significant changes occur in PaO2, pCO2 and pH when weaning INO in INO-responsive neonates. Unlike the change in PaO2, the magnitude of change in pCO2 and pH are unlikely to be clinically significant. INO reductions induce minimal changes in respiratory parameters while discontinuations exert significant differences. These findings provide additional evidence to support the hypothesis that the neonatal dose-response for INO therapy extends into the ppb range.