We investigated the effect of inhaled NO (iNO) on ADP-dependent platelet activation in newborns with PPHN. After parental informed consent, infants with PPHN were randomly assigned to receive conventional treatment or treatment with 40 ppm of iNO. Platelet activation was measured at time of entry and 30 minutes later by surface expression of P-selectin in response to increasing concentrations of the agonist ADP (0, 2, 5, 10 and 20 μM). Platelets were fixed, washed and incubated with monoclonal antibodies specific for P-selectin. P-selectin expression was quantified (as mean fluorescence) with fluorescence-activated flow cytometry. We enrolled 11 infants in the iNO group and 13 in the conventionally-treated group. Median P-selectin fluorescence for each group is plotted at baseline and at 30 minutes against ADP concentration. At 30 minutes after enrollment there were no statistically significant changes from baseline fluorescence in either group of patients and at all ADP concentrations (Wilcoxon-unpaired test with a two-tailed p value of<0.05). Figure

figure 1

We conclude that 30 minutes of exposure to iNO does not inhibit platelet activation in newborn infants with PPHN and does not provide a basis for increased risk of hemorrhagic complications.