Elsevier

The Journal of Pediatrics

Volume 156, Issue 4, April 2010, Pages 542-549.e2
The Journal of Pediatrics

Original Article
Lung Volume and Ventilation Inhomogeneity in Preterm Infants at 15-18 Months Corrected Age

https://doi.org/10.1016/j.jpeds.2009.10.017Get rights and content

Objective

To assess whether lung volume and ventilation inhomogeneity in preterm infants at 15-18 months corrected age, and the change in these outcomes from the newborn period to 15-18 months corrected age, depend on gestational age (GA) at birth and the severity of neonatal lung disease.

Study design

Preterm (GA range, 23-32 weeks) and term healthy control infants were studied in quiet sedated sleep at 15-18 months corrected age by multiple breath washout with 5% sulfur hexafluoride using an ultrasonic flowmeter. Valid measurements were obtained from 58 infants. Multivariate and multilevel regression was used to analyze outcomes.

Results

Functional residual capacity (FRC), lung clearance index, and first and second to zeroeth moment ratios were calculated. After accounting for body size at test, FRC at follow-up, and the increase in FRC from the newborn period to 15-18 months corrected age were positively associated with GA and negatively associated with the duration of endotracheal ventilation. Indices of ventilation inhomogeneity were unaltered by GA and the duration of endotracheal ventilation.

Conclusions

In very preterm infants, GA and the duration of endotracheal ventilation are independently associated with reduced lung volume and lung growth during infancy, although the effect size of these findings is small.

Section snippets

Methods

This study was designed as a prospective follow-up study of infant lung function at 15-18 months corrected age. The study design was approved by the Women's and Children's Health Service Research Ethics Committee. Written informed parental consent was obtained before enrollment.

Infants born at King Edward Memorial Hospital (KEMH) in Perth, Western Australia, between April 2005 and September 2006 were recruited for lung function studies at 15-18 months corrected age (i.e., 15-18 months after the

Baseline Characteristics and Test Occasion Details

As anticipated, there were significant differences in baseline characteristics between the preterm and term control infants, as well as between the preterm infants with and without BPD. Preterm infants were tested at marginally higher PMA but were lighter and had lower weight z-score, body mass index (BMI), and BMI z-score compared with term control infants; preterm infants with BPD had lower GA and birth weight but did not differ in body size or body proportions at test compared with preterm

Discussion

In this follow-up study, FRC at 15-18 months corrected age, and the increase in FRC from the newborn period to follow-up, were positively associated with maturity at birth and negatively associated with the duration of ventilation and exposure to postnatal corticosteroids after adjusting for length and length z-score at test. LCI and moment ratios at 15-18 months corrected age were unaltered by GA, duration of ventilation, and postnatal corticosteroids. These findings support current concepts

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      Hjalmarson and Sandberg found increased LCI in preterm compared to term infants; importantly, they further demonstrated a strong association between LCI and the severity of BPD in preterm infants measured at term corrected age using nitrogen washout technique (Hjalmarson and Sandberg, 2002, 2005). In contrast, several recent studies failed to confirm those associations (Schulzke et al., 2010; Latzin et al., 2009; Hulskamp et al., 2009). Besides differences in overall equipment setup and methodology, these conflicting results could potentially be explained by confounding factors such as the respiratory dead space to tidal volume ratio (VD/VT) which might influence the association between LCI and BPD: LCI is calculated as the number of lung turnovers (cumulative expired volume at the point where end-tidal inert gas concentration falls below 1/40th of the original concentration), divided by the functional residual capacity (FRC).

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    Supported by a PMH Telethon Clinical Research Fellowship Grant (to S.M.S.), a PMH Research Foundation Grant (to G.L.H.), and a Raine Foundation Priming Grant (to J.J.P.). The authors declare no conflicts of interest.

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