Nasal versus face mask for multiple-breath washout technique in preterm 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.

Infant multiple breath washout using a new commercially available device: Ready to replace the previous setup?

INTRODUCTION

Multiple breath washout (MBW) is a sensitive test to measure lung volumes and ventilation inhomogeneity from infancy on. The commonly used setup for infant MBW, based on ultrasonic flowmeter, requires extensive signal processing, which may reduce robustness. A new setup may overcome some previous limitations but formal validation is lacking.

AIM

We assessed the feasibility of infant MBW testing with the new setup and compared functional residual capacity (FRC) values of the old and the new setup in vivo and in vitro.

METHODS

We performed MBW in four healthy infants and four infants with cystic fibrosis, as well as in a Plexiglas lung simulator using realistic lung volumes and breathing patterns, with the new (Exhalyzer D, Spiroware 3.2.0, Ecomedics) and the old setup (Exhalyzer D, WBreath 3.18.0, ndd) in random sequence.

RESULTS

The technical feasibility of MBW with the new device-setup was 100%. Intra-subject variability in FRC was low in both setups, but differences in FRC between the setups were considerable (mean relative difference 39.7%, range 18.9; 65.7, P = 0.008). Corrections of software settings decreased FRC differences (14.0%, -6.4; 42.3, P = 0.08). Results were confirmed in vitro.

CONCLUSION

MBW measurements with the new setup were feasible in infants. However, despite attempts to correct software settings, outcomes between setups were not interchangeable. Further work is needed before widespread application of the new setup can be recommended.

Effect of equipment dead space on multiple breath washout measures

BACKGROUND AND OBJECTIVE

Multiple breath inert gas washout (MBW) systems are designed to minimize equipment dead space volume (Vd). Animal and infant studies have demonstrated the impact of increased Vd on MBW measurements. In this study, we investigate the effect of Vd of a nitrogen (N2 ) MBW system on MBW measurements in preschool children.

METHODS

N2 MBW measurements were performed in healthy adults under standard conditions; Vd was added to match the relationship between Vd and lung volumes observed in preschool children. Subsequently, subjects were measured on a sulfur hexafluoride (SF6 ) MBW system under standard conditions and with Vd added to match that of the N2 MBW system. Healthy preschool children and children with cystic fibrosis were tested on both the N2 MBW and SF6 MBW in random order on the same day. A correction equation was derived based on the adult experiments and tested on the preschool data.

RESULTS

Increasing the Vd of the N2 MBW system resulted in a higher lung clearance index (LCI). A strong non-linear relationship between N2 LCI and the Vd/tidal volume was observed. When the Vd was equivalent between systems, LCI measured by the SF6 MBW system was similar to that measured by the N2 MBW. LCI was higher on the N2 MBW than the SF6 MBW in preschool children. Correcting for the equipment Vd of the N2 MBW resulted in better agreement.

CONCLUSIONS

Equipment Vd affects LCI measurements especially in young children where Vd is large relative to lung volumes.

Lung clearance index: evidence for use in clinical trials in cystic fibrosis

The ECFS-CTN Standardisation Committee has undertaken this review of lung clearance index as part of the group's work on evaluation of clinical endpoints with regard to their use in multicentre clinical trials in CF. The aims were 1) to review the literature on reliability, validity and responsiveness of LCI in patients with CF, 2) to gain consensus of the group on feasibility of LCI and 3) to gain consensus on answers to key questions regarding the promotion of LCI to surrogate endpoint status. It was concluded that LCI has an attractive feasibility and clinimetric properties profile and is particularly indicated for multicentre trials in young children with CF and patients with early or mild CF lung disease. This is the first article to collate the literature in this manner and support the use of LCI in clinical trials in CF.

Nasal versus oronasal raised volume forced expirations in infants--a real physiologic challenge

Raised volume rapid thoracoabdominal compression (RTC) generates forced expiration (FE) in infants typically from an airway opening pressure of 30 cm H(2)O (V(30)). We hypothesized that the higher nasal than pulmonary airway resistance limits forced expiratory flows (FEF(%)) during (nasal) FE(n), which an opened mouth, (oronasal) FE(o), would resolve. Measurements were performed during a brief post-hyperventilation apnea on 12 healthy infants aged 6.9-104 weeks. In two infants, forced expiratory (FEFV) flow volume (FV) curves were generated using a facemask that covered the nose and a closed mouth, then again with a larger mask with the mouth opened. In other infants (n = 10), the mouth closed spontaneously during FE. Oronasal passive expiration from V(30) generated either the inspiratory capacity (IC) or by activating RTC before end-expiration, the slow vital capacity ((j) SVC). Peak flow (PF), FEF(25), FEF(50), FEF(25-75), FEV(0.4), and FEV(0.5) were lower via FE(n) than FE(o) (P < 0.05), but the ratio of expired volume at PF and forced vital capacity (FVC) as percent was higher (P < 0.05). FEF(75), FEF(85), FEF(90), FVC as well as the applied jacket pressures were not different (P > 0.05). FEFV curves generated via FE(o) exhibited higher PF than FV curves of IC (P < 0.05); PF of those produced via FE(n) were not different from FV curves of IC (P > 0.05) but lower than those of (j) SVC (P < 0.05). In conclusion, the higher nasal than pulmonary airways resistance unequivocally affects the FEFV curves by consistently reducing PF and decreases mid-expiratory flows. A monitored slightly opened mouth and a gentle anterior jaw thrust are physiologically integral for raised volume RTC in order to maximize the oral and minimize nasal airways contribution to FE so that flow limitation would be in the pulmonary not nasal airways.

Lung volume and ventilation inhomogeneity in preterm infants at 15-18 months corrected age

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.