Changes in minute ventilation after exposure to 4% sulfur hexafluoride (SF6 ) in infants

Preschool Multiple-Breath Washout Testing. An Official American Thoracic Society Technical Statement

BACKGROUND

Obstructive airway disease is nonuniformly distributed throughout the bronchial tree, although the extent to which this occurs can vary among conditions. The multiple-breath washout (MBW) test offers important insights into pediatric lung disease, not available through spirometry or resistance measurements. The European Respiratory Society/American Thoracic Society inert gas washout consensus statement led to the emergence of validated commercial equipment for the age group 6 years and above; specific recommendations for preschool children were beyond the scope of the document. Subsequently, the focus has shifted to MBW applications within preschool subjects (aged 2-6 yr), where a "window of opportunity" exists for early diagnosis of obstructive lung disease and intervention.

METHODS

This preschool-specific technical standards document was developed by an international group of experts, with expertise in both custom-built and commercial MBW equipment. A comprehensive review of published evidence was performed.

RESULTS

Recommendations were devised across areas that place specific age-related demands on MBW systems. Citing evidence where available in the literature, recommendations are made regarding procedures that should be used to achieve robust MBW results in the preschool age range. The present work also highlights the important unanswered questions that need to be addressed in future work.

CONCLUSIONS

Consensus recommendations are outlined to direct interested groups of manufacturers, researchers, and clinicians in preschool device design, test performance, and data analysis for the MBW technique.

[Lung clearance index in cystic fibrosis]

INTRODUCTION

Small airways' involvement in cystic fibrosis (CF) pulmonary disease is a very early event, which can progress sub-clinically and insidiously since it is poorly reflected by commonly used lung function tests.

STATE OF ART

Sensitive and discriminative tools are available to investigate small airways function. However their complexity and/or invasiveness has confined their use to research purposes and to some specialized research teams. By contrast, the multiple breath washout (MBW) test is more affordable and non-invasive. Lung clearance index (LCI), which is the most used derived parameter, is reproducible and much more sensitive than spirometry in detecting small airways disease. However, MBW is operator dependent.

PERSPECTIVES

The recent commercialization of devices assessing LCI launches MBW as a potential tool in routine clinical care, although its use currently remains mostly dedicated to research purposes. However, important differences in LCI between various equipment settings raise a number of theoretical questions. Specific algorithms should be refined and more transparent. Standardization of MBW is still an ongoing process. Whether other MBW derived indices can prove superior over LCI deserves further study.

CONCLUSIONS

In CF, LCI is now a well-established outcome in research settings to detect early lung function abnormalities and new treatment effects, especially in patients with mild lung disease. In these patients, LCI seems an attractive tool for clinicians too. Yet, further investigation is needed to define clinically significant changes in LCI and to which extent this index can be useful in guiding clinical decisions remains to be studied.

The effect of inert gas choice on multiple breath washout in healthy infants: differences in lung function outcomes and breathing pattern

The detrimental effects on breathing pattern during multiple breath inert gas washout (MBW) have been described with different inhaled gases [100% oxygen (O₂) and sulfur hexafluoride (SF₆)] but detailed comparisons are lacking. N₂- and SF₆-based tests were performed during spontaneous quiet sleep in 10 healthy infants aged 0.7-1.3 yr using identical hardware. Differences in breathing pattern pre and post 100% O₂ and 4% SF₆ exposure were investigated, and the results obtained were compared [functional residual capacity (FRC) and lung clearance index (LCI)]. During 100% O₂ exposure. mean inspiratory flow ("respiratory drive") decreased transiently by mean (SD) 28 (9)% ( P < 0.001), and end-tidal CO₂ (carbon dioxide) increased by mean (SD) 0.3 (0.4)% units ( P < 0.05) vs. air breathing prephase. During subsequent N₂ washin (i.e., recovery phase), the pattern of change reversed. No significant effect on breathing pattern was observed during SF₆ testing. In vitro testing confirmed that technical artifacts did not explain these changes. Mean (SD) FRC and LCI in vivo were significantly higher with N₂ vs. SF₆ washout: 216 (33) vs. 186 (22) ml ( P < 0.001) and 8.25 (0.85) vs. 7.55 (0.57) turnovers ( P = 0.021). Based on these results, SF₆ based MBW is the preferred methodology for tests in this age range. NEW & NOTEWORTHY Inert gas choice for multiple breath inert gas washout (MBW) in infants has important consequences on both breathing pattern during test performance and the functional residual capacity and lung clearance index values obtained. Data suggest the detrimental effect of breathing pattern of 100% O₂ and movement of O₂ across the alveolar capillary membrane, with direct effects on MBW outcomes. SF₆ MBW during infancy avoids this and can be further optimized by addressing the sources of technical artifact identified in this work.