MONTREAL — A diagnosis of chronic lung disease of prematurity did not predict reduced lung function in childhood in a study of long-term respiratory outcomes in children born extremely prematurely.
But the study provided evidence that postnatal corticosteroid use is associated with reduced childhood lung function, although a causal relationship could not be definitively established, Ms. Lucia Smith said at the Seventh International Congress on Pediatric Pulmonology.
The lack of association of reduced lung function with chronic lung disease of prematurity (CLDP) runs contrary to traditional opinion in the literature, which suggests lung function is significantly reduced in children with CLDP.
“Most older studies have tended to compare children with CLDP with term controls rather than preterm controls, but our results are consistent with results in recent studies in CLDP cohorts,” Ms. Smith said in an interview.
The cross-sectional study included 126 children born between 1992 and 1994 at a mean gestational age of 27 weeks, who were recruited from the New South Wales, Australia, neonatal intensive care units database, and 34 age-matched controls who were born full term. The average weight at birth was 862 g for the children born prematurely, compared with 3,420 g for the children born full term.
Medical records available for 104 preterm children showed 37 (35.5%) had CLDP, defined as any infant who was still dependent on supplemental oxygen at 36 weeks, and 46 of the 104 (44%) had received systemic corticosteroids at any time during the initial neonatal intensive care unit stay immediately after birth.
There was no difference in spirometry between children born prematurely who were diagnosed with CLDP as neonates and those who were not, said Ms. Smith, a PhD candidate at the University of Sydney, New South Wales, and her associates.
Spirometry values were significantly lower in the preterm group, compared with controls: mean forced vital capacity, 96% vs. 102%; mean forced expiratory volume in 1 second (FEV1), 85% vs. 95%; and forced expiratory flow at 25%–75% of forced vital capacity (FEF25%–75%), 72% vs. 91%.
The preterm children who received postnatal corticosteroids had significantly lower flows than those who did not (FEV1, 82% vs. 88% and FEF25%–75%, 65% vs. 78%). These measures were within “normal limits” for lung function, Ms. Smith said.
In a regression analysis, cumulative steroid use, age of first steroid dose, birth weight, gestation, number of days intubated, or maximum oxygen concentration had no relationship with lung function.
“Our results highlight the fact that the definition of CLDP uses an arbitrary cut off of oxygen requirement at 36 weeks' gestational age,” Ms. Smith said. “There are no standardized criteria to assist the decision to cease supplemental oxygen, and it is likely to differ in different neonatal units.”
In reality, a number of children in the non-CLDP group may have only just come off supplemental oxygen by 36 weeks, she said. Likewise, some in the CLDP group may not have needed oxygen at 36 weeks, Ms. Smith added, thus the lack of association of reduced lung function with CLDP.
In a question-and-answer session, audience members called the corticosteroid data fascinating, but posited that a number of the preterm children must have fallen outside of “normal” limits for lung function. Ms. Smith said there was a range of results, particularly in airway flow, both for those preterm children who received steroids and those who did not. Data that were not presented indicate that fitness and exercise tolerance are markedly reduced in the entire preterm group, with results less than 50% of those in the control group, she said.