Survival rate and prevalence of bronchopulmonary dysplasia in extremely low birth weight infants

Background: Bronchopulmonary dysplasia (BPD) continues to represent a significant cause of morbidity among survivors of severe prematurity in the NICU. The increasing prevalence of BPD over the decades has been suggested to be related to the increased survival of extremely low birthweight infants.

Aims: To evaluate differences in prevalence of BPD (BPD28d and BPD36wk) and as a function of survival rate in extremely low birth weight (ELBW) infants over time, and to explore its relationship with known associated risk factors.

Methods: Survival rate and prevalence of oxygen-dependency =28 days (BPD28d) and oxygen-dependency =36 weeks postmenstrual age (BPD36wk) were evaluated in ELBW newborns (mean gestational age: 27.12.2 weeks; mean birth weight: 817142 g) consecutively admitted to the Brindisi NICU over the last 26 years. Two arbitrarily chosen time periods were compared: Period 1: July 1st, 1986 to June 30, 2002 vs. Period 2: July 1st, 2002 to December 31, 2012. Analyzed variables included gestational age, birth weight, intubation time, hours of O2 administration, NCPAP, and use of surfactant. Differences between the time periods were assessed by chi-square statistics, Fisher's tests or Mann-Whitney test, as appropriate. A two-tailed p value <0.05 was considered to indicate statistical significance.

Results: Survival rate of ELBW infants over the examined time periods dramatically improved from 42.3% to 72.6% (p < 0.0001), whereas changes in the prevalence of BPD28d and BPD36wk were not statistically significant (30.5% vs. 39.3%, p = 0.2137 and 5.5% vs. 13.1%, p = 0.1452, respectively). Likewise, BPD severity was not significantly different between the two time periods (p = 0.1635). Gestational age and birth weight of surviving neonates did not significantly change between the two time periods (p = 0.8050 and p = 0.6986, respectively), whereas significantly increased intubation time (median values: 144 hours vs. 33 hours, p <0.0001) and use of exogenous surfactant (89.3% vs. 48.6%, p < 0.0001) was evidenced for the second time period, as well as NCPAP (median values: 600 hours vs. 377 hours, p = 0.0005). A statistically non-significant trend for a prolonged O2 administration in period 2 (p = 0.0850) was also observed.

Conclusion: Our findings indicate that a significantly increased survival is not necessarily associated with a significant difference in the prevalence of BPD among ELBW infants.