Impaired Gas Mixing and Low Lung Volume in Preterm Infants with Mild Chronic Lung Disease

Abstract

The aim of this study was to assess the possible role of gas mixing inefficiency in spontaneously breathing infants with mild chronic lung disease (CLD) of prematurity in relation to changes in other functional parameters. A simple bedside technique for recording and analysis of multiple breath nitrogen washout curves was applied together with occlusion mechanics. Fifteen preterm infants with mild or moderately severe CLD were studied at a mean postconceptional age of 35 wk, together with 15 healthy preterm infants at the same maturity. All infants breathed spontaneously, and the test was performed by a continuous bypass flow system, connected to a face mask, a pneumotachograph, and a nitrogen meter. The results showed impaired gas mixing with moment ratios above the 95th percentile of the normal group in 11/15 infants with CLD. Functional residual capacity (FRC) was low in 13/15 infants, but specific compliance and resistance of the respiratory system did not differ between the groups. As FRC and moment ratios were not correlated, it is suggested that they may reflect different aspects of the pathophysiology in CLD. It is concluded that low FRC and disturbed gas mixing are characteristic disturbances in CLD at different degrees of severity. The multiple breath nitrogen washout test, followed by moment analysis of end-tidal nitrogen concentrations, is a simple and sensitive method for detection of these disturbances and for monitoring purposes.

N-Acetylcysteine Administration during the First Week of Life Does Not Improve Lung Function in Extremely Low Birth Weight Infants

“…However, we found no such beneficial effect on lung function by NAC. We conclude that the infants examined in the present study all had lung function abnormalities similar to what we previously found in infants with BPD examined at the same age [24] and thus constituted a suitable target group for the intervention. The lack of a discernable effect on lung function and on the incidence of BPD in the main clinical trial [18] might be sought in a faulty basic rational or in the design and implementation of the trial.…”

“…However, with the drug dosage used, no beneficial effect on the incidence of BPD or death at the age corresponding to 36 gestational weeks could be found [18]. We and others have previously shown that infants with BPD show characteristic functional abnormalities at term [24]. FRC is reduced and gas mixing efficiency is impaired.…”

Inert Gas Washout: Theoretical Background and Clinical Utility in Respiratory Disease

“…The discrepancies seen in earlier N 2 MBW infant [48], paediatric [19, 37,103,104,105] and adult [45, 104] studies may relate to external equipment dead-space and whether dead space was adequately corrected for in subsequent calculations. It also highlights the need for more current N 2 MBW normative data.…”

“…Studies in smaller patient groups, discussed in more detail by recent review articles [99, 100], have suggested elevated gas trapping (as assessed by FRC pleth and FRC N2 ) and LCI (or MR) in infants with BPD in the newborn period in comparison to healthy controls [48, 101]. However, a recent larger multicentre study has suggested that this actual difference between the healthy controls and infants with BPD may be much smaller once additional contributing factors such as prematurity and intrauterine growth are taken into account [102].…”

“…Truncation of the MR plot to, for example, 8 or 10 TO is necessary to facilitate comparison between subjects. Moment analysis avoids problems associated with defining the end point of washout in patients with more severe obstructive disease and gas trapping, and may compensate for variations in the respiratory rate and tidal volume during the washout [20, 48]. Whilst there is a lack of consensus as to which index is the most appropriate to use, LCI is more commonly reported in the literature and, in our experience, is a robust parameter, whereas MR do not appear to offer additional information or benefit.…”