NPPB and bronchopulmonary dysplasia: Kaplan-Meier survival analysis shown in Figure 3 demonstrated significantly lower survival for subjects with peak BNP level of ≥ 220 pg/ml After controlling for age, sex, and BPD severity, multivariate Cox proportional hazards modeling showed that a BNP level of ≥ 220 pg/ml independently increased the likelihood of death (hazard ratio 5.1, 95% CI 1.1 to 22.4, P = 0.03).