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Preschool Multiple-Breath Washout Testing An Official American Thoracic Society Technical Statement Paul D. Robinson, Philipp Latzin, Kathryn A. Ramsey, Sanja Stanojevic, Paul Aurora, Stephanie D. Davis, Monika Gappa, Graham L. Hall, Alex Horsley, Renee Jensen, Sooky Lum, Carlos Milla, Kim G. Nielsen, Jessica E. Pittman, Margaret Rosenfeld, Florian Singer, Padmaja Subbarao, Per M. Gustafsson*, and Felix Ratjen*; on behalf of the ATS Assembly on Pediatrics

THIS OFFICIAL TECHNICAL STATEMENT OF THE AMERICAN THORACIC SOCIETY WAS APPROVED DECEMBER 2017.

Background: Obstructive airway disease is nonuniformly distributed Results: Recommendations were devised across areas that place throughout the bronchial tree, although the extent to which this occurs can specific age-related demands on MBW systems. Citing evidence where vary among conditions. The multiple-breath washout (MBW) test offers available in the literature, recommendations are made regarding important insights into pediatric lung disease, not available through spirometry procedures that should be used to achieve robust MBW results in the or resistance measurements. The European Respiratory Society/American preschool age range. The present work also highlights the Thoracic Society inert gas washout consensus statement led to the emergence important unanswered questions that need to be addressed in of validated commercial equipment for the age group 6 years and above; future work. specific recommendations for preschool children were beyond the scope of the document. Subsequently, the focus has shifted to MBW applications within Conclusions: Consensus recommendations preschool subjects (aged 2–6 yr), where a “window of opportunity” exists for are outlined to direct interested groups of manufacturers, early diagnosis of obstructive lung disease and intervention. researchers, and clinicians in preschool device design, test performance, and data analysis for the MBW Methods: This preschool-specific technical standards document technique. was developed by an international group of experts, with expertise in both custom-built and commercial MBW equipment. A Keywords: multiple-breath washout; lung clearance index; comprehensive review of published evidence was performed. peripheral airway function; cystic fibrosis

Contents Optimal Synchronization of Flow Recommendations for Overview and Inert Gas Concentration Commercial Software Introduction Technical Considerations Reference Data for Preschool MBW Methods regarding Inert Gas Choice MBW Use in Preschool Interventional Background Physiological and Developmental Research Studies Technical Considerations for Considerations for Preschool MBW Minimal Clinically Important Preschool MBW Physiological Considerations of Difference Validation of FRC Measurement Inert Gas Choice Future Work and Conclusions Accuracy Equipment-related VD Flow Measurement and Breath Environment for Testing Detection Preschool Test Feasibility

*Joint senior authors.

ORCID IDs: 0000-0001-7397-105X (P.D.R.); 0000-0002-5239-1571 (P.L.); 0000-0003-4574-6917 (K.A.R.); 0000-0001-7931-8051 (S.S.); 0000-0002-9390-0651 (S.D.D.); 0000-0002-6801-7883 (M.G.); 0000-0002-6217-9494 (G.L.H.); 0000-0003-1828-0058 (A.H.); 0000-0002- 0877-9579 (R.J.); 0000-0001-5515-3053 (C.M.); 0000-0001-6684-3527 (K.G.N.); 0000-0003-3789-1241 (J.E.P.); 0000-0002-8105-614X (M.R.); 0000-0003-3471-5664 (F.S.); 0000-0003-0394-1933 (P.S.); 0000-0001-6485-007X (P.M.G.); 0000-0003-4057-6592 (F.R.). Correspondence and requests for reprints should be addressed to Paul D. Robinson, M.B. Ch.B., Ph.D., Department of Respiratory Medicine, Children’s Hospital at Westmead, Locked Bag 4001, Westmead, NSW 2145, Australia. E-mail: [email protected]. An Executive Summary of this document is available at http://www.atsjournals.org/doi/suppl/10.1164/rccm.201801-0074ST. Am J Respir Crit Care Med Vol 197, Iss 5, pp e1–e19, Mar 1, 2018 Copyright © 2018 by the American Thoracic Society DOI: 10.1164/rccm.201801-0074ST Internet address: www.atsjournals.org

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Overview historical preschool feasibility, achieved document; interested readers are directed to with custom-built research-based existing literature elsewhere (14, 15). The incorporation of preschool multiple- equipment, within the clinical setting breath washout (MBW) testing into using commercial equipment (or fi research and clinical practice is growing, as modi ed versions), have been Introduction is evident by the increasing number of unsuccessful (11, 12). – publications in this area. Initial review This technical standards document In preschool children (2 6 yr of age), articles on preschool MBW appeared in aims to build on and complement existing conventional lung function tests, such as 2005 (1) and 2006 (2), and were documents in the literature, as part of the spirometry, remain technically challenging supplemented in 2007 by a formal MBW process toward clarifying the clinical utility and relatively insensitive in identifying section within an official American of MBW within the preschool age range. early airway disease in conditions such as – Thoracic Society/European Respiratory It outlines important recommendations on CF (16 18). MBW for this age group has device design for manufacturers and test emerged as a feasible outcome measure for Society (ATS/ERS) statement on preschool fi lung function testing (3). The ATS/ERS performance for operators that are speci c interventional studies and an area of document highlighted that “few systems for to preschool children. It recognizes that interest for clinicians exploring its utility in MBW adapted for the preschool age group although there are still areas that require clinical care. A Cystic Fibrosis Foundation [were] commercially available,” and that further data for formal standardization, a report, based on the discussions within a remains the case a decade later. The number of important recommendations can workshop hosted by the North American be made that should be implemented to CF Foundation and Therapeutics ERS/ATS inert gas washout consensus standardize the technique across institutions Development Network, concluded that document (hereafter termed the ERS/ATS as the technique moves toward widespread MBW was “a valuable potential outcome consensus statement), published in 2013, clinical use. Current recommendations are measure for CF clinical trials in preschool- represented an important step forward for based on consensus, citing evidence where aged patients” (15). This was echoed in the overall technique, providing available in the literature, across an concurrent recommendations from the recommendations for manufacturers and international group of experts (Table 1). European Cystic Fibrosis Society Clinical researchers interested in MBW equipment, For aspects where different acceptable Trial Network (ECFS-CTN) testing protocol, and data analysis (4). options exist, discussion focuses on the Standardisation Committee, which Although all age groups were mentioned, “ fi advantages and disadvantages of each highlighted the strong evidence base to speci c preschool recommendations were option. The expertise gathered spans support the use.in clinical trials in CF” limited to brief statements about testing several types of research and commercial (14). The vast majority of MBW studies in interface and position. Increasing interest MBW equipment. The majority of both this age range have focused on CF, with in preschool MBW is now being driven by research and commercial systems employed studies of other respiratory conditions the potential utility of MBW outcomes such – fi to date have been open circuit based including but not focusing on preschool as the lung clearance index (LCI) in speci c systems, although the utility of closed, subjects (19, 20). patient groups (e.g., those with cystic rebreathing setups is also being explored by fi brosis [CF]), where MBW is being used as some groups (13). Close collaboration an outcome measure for clinical trials. between researchers and manufacturers has Methods Publications in this area have trebled over been a key aspect in achieving progress to each successive 5-year period of the past 15 date for MBW, and will be essential for The working group was assembled to years (5). ongoing standardization work within this develop detailed technical standards for the Although commercial MBW younger age range. performance of MBW in the preschool age equipment exists, these devices have not Important areas that need to be range, which were lacking in the original fi been developed speci cally for the unique addressed in future work are outlined and ERS/ATS consensus document (4). As with requirements of the preschool age group. summarized in Table 2 and will, it is hoped, the previous document this work was based Several challenges encountered when using prove an incentive to gather the evidence largely on consensus, but sought to clearly these commercially available devices with necessary for further advances in describe evidence when available. Expert preschool children need to be standardization within this age group. The knowledge was supplemented by a considered by manufacturers, as well as overall focus of this document is on MBW comprehensive review of the literature researchers/clinicians. Higher respiratory and reports mainly on LCI and the (both of published abstracts and articles rates, lower respiratory flows, and lower experience gained to date through studies contained within Embase and PubMed lung volumes in preschool children place in CF, as the most commonly utilized index databases) performed with the keywords additional demands on equipment and disease group, respectively. Other MBW, preschool children, preschoolers, performance. This may account for the MBW indices have shown promise in CF, LCI, moment ratios, moment analysis, and lower accuracy observed against smaller but understanding of utility remains behind FRC, as of October 31, 2017. Members of lung model volumes in some of the previous that of LCI. The role of these indices and the working group were selected by the validation efforts in the literature (6, 7). the general utility of MBW in other chair (Paul D. Robinson), based on Success in the infant age range illustrates respiratory conditions need to be explored involvement with the previous ERS/ATS that these can be overcome (8–10). In in future work. Challenges of defining consensus work, published in 2013, and/or addition, initial attempts to replicate high clinical utility are not discussed within this active research or interest in preschool e2 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

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Table 1. Summary of Key Current Recommendations for Manufacturers and Multiple-Breath Washout Operators

Manufacturer Directed Operator Directed

Compliance with preschool recommendations: commercial MBW systems d Manufacturers must provide sufficient information and complete transparency d The end user is encouraged to demand this as part to the end user regarding their ability to comply with the preschool of the marketing material accompanying any device. recommendations contained within this document. Validation of FRC measurement accuracy d In vitro validation for preschool MBW systems must include representative FRC volumes of the preschool age range, using respiratory rates and VT typical for the subjects and lung conditions encountered. d FRC measurement accuracy must not be extrapolated from larger FRC volumes. Flow measurement and breath detection d VT accuracy must be within 3% or 5 ml, whichever is greater. d Flow detection accuracy must be robust and manufacturer assessment based on data mimicking the variability in breathing pattern encountered in this age group. d Breath detection software must handle the pauses in breathing and fragmented breaths frequently encountered in this age range. The approaches used must be fully transparent to the user. Optimal synchronization of flow and inert gas concentration d Synchronization error must be within 10 ms across the duration of the entire d The operator must have the ability to assess the washout. accuracy of inert gas concentration and flow d The presence of flow dependence, gas viscosity, and density effects on synchronization at the time of testing. synchronization of flow and inert gas concentration signals must be assessed within MBW systems evaluated for preschool testing. Manufacturers are encouraged to incorporate dynamic synchronization methods that correct for these factors, if present, to improve MBW system accuracy. Inert gas choice d To date, there is no clear evidence to suggest which inert gas is most suitable for the preschool age range, with respect to technical, physiological effects and feasibility. Both SF6-andN2-based MBW appear appropriate inert gas choices for preschool children. d Preschool MBW systems must provide the ability to monitor breathing pattern in real time during each test. d Until the magnitude of error introduced and validated correction equations are available for inert gas diffusion across the alveolar–capillary barrier, correction of MBW data for this effect is not recommended.

Equipment-related VD d Manufacturers must minimize equipment-related VD. To ensure a consistent d MBW operators must minimize facemask-associated approach across age ranges, equipment-related VD must be kept below 2 VD by ensuring that the smallest appropriately sized ml/kg, as recommended in the recent ERS/ATS consensus guidelines. facemask is used, and by using therapeutic putty d Efforts to minimize VD within an MBW system must not adversely affect overall within the facemask to ensure no obstruction to resistance of the breathing circuit such that breathing pattern is altered. airflow occurs.

Environment for testing d The environment for preschool MBW testing should be as child-friendly and safe as possible, including ensuring it is quiet, contains suitable preschool furniture and decoration, and accommodates adult supervision during testing. d Adequate time should be set aside for testing in this age group, particularly for those less than 4 yr of age or who are attending for the first time. An hour is recommended for initial testing. d Familiarization visits for the child and parents to experience equipment, testing procedure, test interface, and environment used during testing are recommended. d Adequate distraction during the assessment is essential and must be enough to take the child’s attention away from his/her breathing, the operator, and the immediate surroundings during each test. Appropriate choice of movie is critical to the process d Two operators should be used for MBW testing in this age group, regardless of interface choice. (Continued)

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Table 1. (Continued)

Manufacturer Directed Operator Directed

Testing interface d Both a mouthpiece and nose-clip assembly and a facemask are supported d At the present time these interfaces must not be as interface choices for use in preschool-aged children. viewed as interchangeable within this age range, and careful consideration of interface choice is strongly recommended. Special considerations when reporting preschool MBW data d Software must clearly state where reported indices values are “based on d The approach to individual and overall test session the average of two values alone.” acceptability in preschool children should be adapted d The previously recommended FRC 10% acceptability criterion for LCI to reflect differences in comparison with older reporting is no longer advocated in this age group. subjects: preschool children require a shorter duration of pretest breathing stability; may have greater variability in EELV and VT during normal tidal breathing; and swallows, pauses, and sighs may occur more frequently during the test. d Until definitive evidence is available for preschool children, MBW operators are strongly encouraged to perform three technically acceptable tests. Outcomes derived from only two acceptable tests must be clearly identified as when results are reported in software. Recommendations for online software requirements for manufacturers d Software must enable adequate visual quality control of the volume, flow, and inert tracer gases for the entire duration of the test. d Software quality control cannot be automated until clear evidence-based thresholds are available. d Incentive software is not recommended in this age range. Reference data for MBW in preschool age range d Available reference data from older subjects must not be extrapolated to d Until robust device-specific reference equations are the preschool age range. published for commercial systems, research groups d Collaborative efforts to achieve robust preschool-specific reference data must ensure that studies collect appropriately are strongly recommended. matched healthy control data.

Definition of abbreviations: ATS = American Thoracic Society; EELV = end-expiratory lung volume; ERS = European Respiratory Society; LCI = lung clearance index; MBW = multiple-breath washout; SF6 = sulfur hexafluoride.

MBW research. International children in studies did not occur until two with a “snug fitting mask system” might representation across the main current decades later (23, 24). Initial data collected allow feasible MBW measurements in even commercial devices was intentionally in the 1980s suggested poor feasibility in younger children. Incorporation of a targeted. As with the previous ETS/ATS preschool children. Using custom-built facemask-based interface was not reported consensus statement, this provided wider equipment, Couriel and colleagues reported until 2003; Gustafsson and colleagues used applicability for current recommendations feasibility of 49% in 82 subjects aged a facemask interface and replaced music to be adopted in future MBW equipment 3.9–6.8 years (23). Couriel and colleagues with video-based distraction, but did not and testing protocols. All potential conflicts used an airtight snorkel mouthpiece and report feasibility rates (25). Shortly after, of interest were disclosed and managed nose-clip interface and a two-way breathing Aurora and colleagues, in 2005, used this according to the policies and procedures for valve, and reported “great difficulty” with approach in preschool children and ATS projects. Individual sections were the technique. The authors stated “fear of achieved feasibility of 79% across 77 drafted by smaller working groups, merged the apparatus was the main cause of failure subjects aged 2–6 years, based on stricter in the overall draft document by the chair, in the younger children” and “major criteria of three acceptable tests (16). and all authors provided comment and difficulty.maintaining a leak-free suggestions for the final document. The connection to the apparatus for the methods checklist is presented in Table 3. duration of the test.” Later the same year, Technical Considerations for Wall reported 80% feasibility in 40 subjects Preschool MBW aged 3–6 years, based on two acceptable Background tests (24). Importantly, Wall’s testing The original ERS/ATS consensus statement protocol incorporated distraction using a included a comprehensive list of Publications including pediatric MBW portable music system and headphones. recommendations for both manufacturers testing initially emerged in the 1960s Wall speculated that replacement of the and operators (4). To facilitate standardized (21, 22), whereas the inclusion of preschool mouthpiece and nose-clip interface system measurement and practice, technical e4 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

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Table 2. Important Areas of Interest for Future Work Specific to Preschool Multiple-Breath Washout

Area of Interest Questions and/or Needs

Shortening the duration of testing for Analysis of MBW outcomes during the wash-in portion of each test (e.g., FRC and LCI), preschool subjects from two tests alone (vs. three tests), or abbreviated outcomes (e.g., LCI at 1/20th threshold) offers potential for shortening overall test session duration. This is of particular interest in preschool subjects given the more limited timeframe for cooperation compared with older subjects.

Effects of pure O2 exposure on breathing Further work is required to clarify the magnitude of the effect of inert gas choice on pattern and EELV in preschool subjects breathing pattern during testing, and whether changes affect MBW indices. The age threshold at which the detrimental effects of pure O2 exposure reported in infants disappears needs to be clarified as well as the magnitude of effect on MBW outcomes. Inert gas diffusion across the Further work is required to clarify the magnitude of inert gas diffusion across the alveolar–capillary barrier alveolar–capillary membrane for the common inert gases used and the potential impact on MBW indices. Is the relative contribution of this inert gas diffusion effect greater in preschool subjects compared with older age groups? Can inert gas–specific corrections be developed and applied, and do these need to be age specific? Artifact definition and exclusion Definition of normal preschool breathing pattern and the level at which artifact occurrence should lead to test rejection. Accuracy of flow and volume measurement Because of the lower flows and faster respiratory rates encountered, the relative errors introduced by sample flow, technical drifts, and BTPS correction may be greater in younger subjects. Given the challenges of FRC validation for preschool-specific equipment, is an alternative approach to BTPS correction warranted? The current fixed BTPS correction approach may introduce a greater relative error in preschool subjects due to the smaller flows and faster respiratory rates encountered, as well as the variable contributions of nasal and oral breathing to relative humidity and temperature of expired gas (67). Should a dynamic approach be considered? There is a lack of information about how BTPS conditions change during preschool MBW. Breath detection Optimal approach to breath detection in an age range where breath pauses, low flows, and low volumes are more frequently encountered, as well as the magnitude of effect on MBW outcomes if not addressed. Should the operator have the ability to correct breath detection errors when they occur? How should minimum breath volume be defined and how does the threshold chosen affect accuracy of subsequent calculated MBW indices?

Definition of normal physiological variability Better definition of normal VT and EELV variability in this age range to determine accurate in the preschool age range thresholds for breathing pattern stability Optimal definition of suitable target VT range—defined based on actual weight, ideal body weight, height, or BMI? Definition of normal FRC variability, in comparison with older age groups, so that preschool-specific recommendations for FRC measurement accuracy can be made Interface transition Strategies to reduce the magnitude of effect on MBW indices when changing interfaces between mouthpiece and nose-clip assembly and facemask Definition of best approach and timing of transition

Equipment-related VD Can functional VD within a bacterial filter or facemask assembly be accurately estimated and corrected for across subjects? What is the contribution of increasing relative VD to the change in LCI reference values observed across the preschool age range (79)? What is the optimal method for expressing VD: as a function of weight (ml/kg) or is BMI, percentage of VT, or height more appropriate? Do other indices, which are less sensitive to the effects of VD (e.g., slope index, moment ratios, and alveolar LCI), offer improved utility to LCI? Preschool-specific reference data What is the true effect of lung development across the preschool age range once the impact of other factors such as changing relative equipment-related VD have been removed? Minimal clinically important difference What is a significant difference in an individual with a particular lung disease? What difference signals a clinically important deterioration or risk for relapse or exacerbation? What is a significant difference in a clinical trial (i.e., on a group level)?

Definition of abbreviations: BMI = body mass index; EELV = end-expiratory lung volume; LCI = lung clearance index; MBW = multiple-breath washout.

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Table 3. Methods Checklist detection thresholds should be set slightly higher than the noise of the flow signal and Yes No then back-extrapolated to the previous zero flow crossing. VT, derived from the flow signal, must be accurate to within 3% or Panel assembly Included experts from relevant disciplines with experience across X 5 ml, whichever is greater (30). This the main current commercial equipment exploring utility in the accuracy should not be affected by the gas preschool age range composition of the breath. For example, Included individual who represents the views of patients and society X dynamic viscosity is 10% higher with at large Included methodologist with appropriate expertise NA* 100% O2 versus room air, which results in an overreading of flow with Literature review pneumotachographs by 10% with 100% O Performed in collaboration with a librarian X 2 Searched multiple electronic databases X if the pneumotachographs are calibrated Reviewed reference lists of retrieved studies X with room air. In contrast, ultrasonic flow meters measure flow using the Doppler Evidence synthesis Applied prespecified inclusion and exclusion criteria X effect; therefore, these devices measure Evaluated included studies for sources of bias X linear velocity and are in principle not Explicitly summarized benefits and harms X sensitive to changing dynamic viscosity, or Used PRISMA1 to report systematic review X density (molar mass), within the molar Used GRADE to describe quality of evidence X mass range encountered with current MBW Generation of recommendations inert gas choices. Used GRADE to rate the strength of recommendations NA Manufacturers should be aware that Definition of abbreviations potential errors introduced by higher : GRADE = Grading of Recommendations Assessment, Development, and fl Evaluation; NA = not applicable; PRISMA = Preferred Reporting Items for Systematic Reviews and technical drift and increased sample ow Meta-Analyses. (sampling rate from sidestream gas analysis *Required for guidelines but not technical statements. setups) on measured tidal flows, integrated VT, and MBW outcomes may be relatively greater in preschool children than in older aspects with particular importance to the two-stage approach to assessment. subjects. However, a precise threshold for preschool age range are discussed in further Importantly, in vitro accuracy may not acceptability of technical drift remains detail within this section. directly translate to in vivo accuracy, as unclear. suggested by preliminary data from older Greater variability in breathing age groups (29). Validation of FRC Measurement patterns of preschool children exists, and Accuracy RECOMMENDATIONS: this should be considered for accurate in vitro At present no available models exist In vitro breath detection. Software must be able to to validate the accuracy of ventilation 1. validation for preschool MBW handle pauses in breathing and fragmented inhomogeneity (e.g., LCI) assessment; systems must include representative breaths that are frequently encountered in therefore validation efforts have focused FRC volumes of the preschool age this age range. This capability has been mainly on FRC measurement accuracy, and range, using a range of respiratory demonstrated in variations of custom-built recommendations in more recent rates and VTs appropriate for the research software by authors within this guidelines (4) have provided a framework subjects and lung conditions working group (16, 31, 32) and is therefore for assessment. Success in older age groups, encountered. also feasible for manufacturers. Approaches however, must not be extrapolated to the 2. FRC measurement accuracy must not be used must be fully transparent to the user. preschool age range. Accurate FRC extrapolated from larger FRC volumes. In breaths split or followed by a pause, if no measurement at these smaller volumes inspiration has occurred during the pause presents greater challenges (6, 8); error Flow Measurement and Breath then it should be viewed as the same breath often increases at smaller volumes (26) and Detection and not as two separate breaths. Objective higher respiratory rates (7, 27). In vitro Breath definition may be based on detection thresholds for defining the occurrence of a validation must therefore include of zero flow crossings or by integration of small inspiration (i.e., minimum breath representative FRC volumes of the flows to detect breath volumes reaching a size) need to be formally defined, and the preschool age range (typically 30–40 ml/kg predetermined significant value. Additional approach used by the manufacturer should in health or an FRC range of 0.4–1.0 L), challenges for the manufacturer in the be clearly described. Errors in definition of using respiratory rates and VT values preschool setting are greater breathing inspiration or expiration may introduce typical for the subjects and lung conditions irregularity and the lower tidal flows FRC estimation error, given the encountered (typically 20–40 breaths/min encountered, compared with older children, requirement for accurate measurement in health and up to 60 breaths/min in with typical peak inspiratory and expiratory of expired inert gas volume during the disease, and VT/FRC of 0.2–0.4) (28). flows ranging from 200 to 400 ml/s. To washout portion of the test, corrected for Dry in vitro models (10) and those ensure accurate flow detection, and any reinspired inert gas. Accurate end-tidal incorporating BTPS conditions (6) offer a breath identification, in this setting, flow inert gas concentration is also more e6 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

AMERICAN THORACIC SOCIETY DOCUMENTS challenging because of the more variable time that exists in the system due to On the basis of fixed synchronization breath size and inconsistent volume and analyzer response time 6 gas transit time approaches, FRC accuracy has been flow profiles of preschool breaths. Small (for sidestream sampling). This flow- demonstrated to remain within 5% (the breaths may lead to erroneous early LCI dependent effect has now been specified accuracy threshold) if threshold identification, due to falsely low demonstrated across different commercial synchronization error is not more than end-tidal inert gas values, and the end user equipment, by separate research groups 10 ms between flow and inert gas must be able to examine data closely for (7, 26), and leads to an increasing delay concentration. This threshold appears to this artifact and adjust accordingly. between signals as flow decreases. Therefore be consistent across various equipment The manufacturer must carefully assess it is particularly relevant to preschool MBW systems (27, 35, 38) and formed the basis and report the approach used to ensure the with its lower tidal flow patterns. of this ERS/ATS consensus statement robustness of its product. Assessment Increasing gas dynamic viscosity and recommendation (4). Respiratory rate requires variability in breathing pattern, density may reduce sample flow within the affects this relationship (37), and the range which may be best provided by sidestream sampling line (e.g., Nafion used must be preschool age specific when representative in vivo data or mimicked tubing). The magnitude of this effect, first this source of error is assessed. with a breath simulator. The latter may also described more than 30 years ago (36), will The flow-dependent and viscosity- provide a means to validate VT accuracy depend on the characteristics of the sample dependent effects described above suggest under ambient conditions. Researchers line, the sample flow rate, and the that a dynamic approach to synchronization should consider supplying such data to magnitude of change in viscosity that may further improve accuracy and must be manufacturers, as has occurred with other occurs during the measurement period. considered by manufacturers designing lung function techniques in the past (e.g., This is particularly relevant to N2 MBW preschool MBW systems. The accuracy of spirometry) (33). where O2 concentration varies between 21 the outcome measurement (e.g., FRC) and 100%, and viscosity change may result should not be extrapolated to other RECOMMENDATIONS: in an alteration of flow–inert gas delay outcomes, as the error magnitude may differ 1. VT accuracy must be within 3% or 5 ml, times of over 10% across the washout (7). For example, LCI threshold is whichever is greater. portion of the test (37). Successful dependent on accurate end-tidal inert gas 2. Flow detection accuracy must be robust adjustment for this viscosity affect has been concentration at the end of the washout, and manufacturer assessment must be described within a commercial MBW where viscosity-related effects may be performed based on data mimicking system (10). greatest, yet the relative exhaled inert gas the breathing pattern variability encountered in this age group. 3. Breath detection software must handle the pauses in breathing and fragmented Time delay sensitivity depending on sensor volume offset breaths frequently encountered in this 800 Time delay with 5ml sensor offset age range. The approaches used must be 600 Time delay with 2ml sensor offset fully transparent to the user. 400 Optimal Synchronization of Flow and Inert Gas Concentration 200 As with MBW systems used in older signal (ms) children, optimal synchronization of flow 2 0 and inert gas concentration signals for preschool children is essential (4, 34, 35). −200 Furthermore, this precise synchronization needs to be maintained over the entire Delay in CO −400 washout period. Changes in flow, during −600 the breathing cycle, and in dynamic viscosity and gas density, over the course of −800 the washout, can further complicate this −200 −150 −100 −50 0 50 100 150 200 process and are of increasing significance Flow (mL s−1) the younger the child. If the point of inert gas measurement Figure 1. Simulation of flow-dependent delay between flow and gas concentration signals. (mainstream) or sampling (sidestream) Visualization of the time delay between two sensors depends on the volume between the differs from the respiratory flow two sensors and the flow rate of the measured gas. The simulations were performed assuming both sensors are placed inside a tube with 2 ml (red line) or 5 ml (blue line) of volume measurement point, the delay between flow separating them. Response times of the sensors were assumed to be similar. The time delay and gas concentration will be affected by fl plotted is the time difference by which a gas, flowing at a constant rate, reaches each sensor. variation in ow within the breathing cycle Mathematically, the flow dependence of the time delay can be calculated by the following as the flow front moves between those two relationship: time delay = (volume between sensors) / (flow rate). Delays are symmetric, but measurement points (Figure 1). This flow- depending on the direction of the flow, one sensor will measure the gas first and the other one dependent effect is additional to the delay second, or the other way around.

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AMERICAN THORACIC SOCIETY DOCUMENTS volume contribution to FRC may be in the preschool age range until appropriate impact of the subject’s status during testing far less in this region of the washout. validation has been performed. Infant- (i.e., asleep/sedated in infants vs. alert and Recommendations to minimize flow–gas based validation of an improved awake in preschoolers) is another delay error to not exceed 10 ms error across sidestream-based approach, which avoids important consideration. Initial preschool- the full washout should be adhered to the need for this correction, holds promise specific insight is encouraging, with a strictly, and the operator must be able to for use in preschool subjects but awaits detectable effect, which is much smaller in evaluate the adequacy of synchronization future validation before firm recommendations magnitude than described for infants: a VT across all data collected. canbemade(10,40). change of less than 10% and not present

RECOMMENDATIONS: consistently across individuals (50). It is not felt to be physiologically relevant by this 1. Synchronization accuracy must be Physiological and working group, but the exact effect on within 10 ms across the duration of the Developmental Considerations MBW outcomes remains unclear. entire washout. for Preschool MBW Preschool MBW equipment must afford 2. The presence of flow dependence, gas the operator the ability to examine and detect viscosity, and density effects on Physiological Considerations of Inert these effects. A recommended approach synchronization of flow and inert gas Gas Choice would be to display VT, respiratory rate, and concentration signals must be assessed To date, there is no clear evidence to suggest concurrent end-tidal CO2 (to detect hyper-: within MBW systems evaluated for that one particular inert gas is more suitable or hypoventilation). Display of real-time VE preschool testing. Manufacturers are for the preschool age range, with respect to should also be considered. Until further data encouraged to incorporate dynamic physiological effects and feasibility. Both are available, both SF6- and N2-based MBW synchronization methods that correct SF6-andN2-based MBW appear appropriate remain appropriate inert gas choices for for these factors, if present, to improve inert gas choices for preschool children. preschool children. MBW system accuracy. Effect of inert gas choice on breathing R : 3. The operator must have the ability pattern during testing. Significant deviation ECOMMENDATIONS within the manufacturer’s software to from tidal breathing has been reported in 1. In MBW testing of preschool subjects, assess the accuracy of inert gas infants during both 100% O2 and 4% SF6 both SF and N appear to be – 6 2 concentration and flow synchronization procedures (41 44). The magnitude of appropriate inert gas choices for at the time of testing. effect is not trivial in infants, with 100% O2 preschool children. exposure causing up to a 33% reduction in 2. Preschool MBW systems must provide Technical Considerations regarding VT (41, 44, 45). Proposed explanations the ability to monitor breathing pattern Inert Gas Choice include the effect of absorption atelectasis in real time during each test. To date, there is no clear evidence to suggest on VT or a blunted peripheral chemoreceptor that one particular inert gas is more suitable response to increased arterial oxygenation on Effect of inert gas diffusion across the : – for the preschool age range from a technical respiratory rate and VE (44, 46). An initial alveolar capillary membrane. There are no data currently available to quantify the perspective. priming period of a lower O2 concentration Of the three main inert gases used (e.g., 40%) has been shown to negate the effect impact of inert gas diffusing across the fl – (helium, sulfur hexa uoride [SF6], and N2), in infants (41). This effect is not as pronounced alveolar capillary membrane on measured most research to date has focused on either with SF exposure, at a concentration of 4%, MBW outcomes in preschool subjects. 6 _ SF6 or N2. Helium use has been restricted with data describing significant effects on VE Although N2 is inert, in the sense that mainly to the setting of a secondary only (42, 43). In a direct comparison of the two the human body does not metabolize it, it comparison gas in preschool SF6 studies, methods, this effect observed with SF6 on VT is a soluble gas, and because of the high using custom-built respiratory mass was attributed to a technical artifact rather than partial pressure of the atmosphere, a spectrometer–based equipment that atruephysiologicaleffect (44). A described large amount of N2 is stored within the facilitates dual gas comparison. Other fast- effect on respiratory rate in a sedated cohort body. As a result N2 will diffuse into the responding helium analyzers are currently (42) was not observed in two subsequent alveoli when the partial pressure of N2 is lacking. nonsedated cohorts (43, 44). The degree to lowered, as occurs during N2-based MBW Indirect inert gas concentration which the effect of 100% O2 on breathing using 100% O2 (51, 52). This process of gas analysis approaches have been developed for pattern accounts for the difference observed diffusion across the alveolar–capillary both SF6 and N2 and are discussed between SF6-andN2-based MBW indices (e.g., membrane applies to all gases to differing elsewhere (4). One such method deserves LCI and FRC) remains unclear, but SF6-based degrees, and occurs to lesser degrees, and in further discussion in the setting of MBW is currently the preferred method in the opposite direction, with both SF6 and preschool MBW. The mainstream molar infants (44). helium (53). The magnitude of diffusion – mass based approach to SF6 calculation Although these effects of 100% O2 do and its effect on subsequent MBW requires correction of the molar mass signal not appear to be present in early school-age outcomes has not been adequately for the effect of humidity and temperature children (47), the exact stage at which this described to date, beyond initial modeling fluctuation during the breathing cycle. effect disappears, if in fact it does (48), attempts for N2 MBW (54). Correction algorithms have been validated remains unclear. The effects are likely to act Several factors are likely to influence for use in young infants (39) but not for in an age-, dose-, and disease-dependent the magnitude of the impact of inert gas preschool children and should not be used manner (41, 46, 48, 49), although the diffusing across the alveolar–capillary e8 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

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1 membrane: ) tissue N2 contribution to the commercial devices must consider the interpretation of longitudinal data. No alveolar N2 fraction is likely to be nonlinear equipment-related VD carefully when direct effect on breathing pattern was in nature, due to the influence of varying designing systems for widespread use in detectable in healthy preschool subjects concentration gradients through the general respiratory clinics. Definitions of (VD range of 1.49–2.55 ml/kg), and the washout portion of the test, gas exchange the VD components of an MBW system threshold at which effects on breathing rates, and the fact that time constants for (equipment, anatomical and physiological) pattern occur remains unclear (59). both N2 elimination and lung perfusion will are described in detail in the ERS/ATS Correction algorithms for LCI have been vary across different lung compartments (55); consensus statement (4). Studies in animals proposed (59), but further work is required 2)thesubject’s age, given that lung (57), infants (58), and preschool children before any firm recommendations can be architecture and cardiac output change and adults (59, 60) have consistently made. Recommendations to correct FRC for with age (particularly relevant in preschool demonstrated detrimental impacts of VD do exist and are routinely applied in subjects, in whom these change more increased VD on ventilation inhomogeneity practice (4). The impact of increased VD on rapidly than in older subjects); and outcomes. Adult data illustrating this EELV and therefore FRC measurement is finally 3) the degree of ventilation increasing detrimental effect of VD on LCI currently unclear. inhomogeneity present and the washout across the VD range of 0–5 ml/kg are shown Preschool children are often tested with time (both of which are typically lower in Figure 2. The fact that there was no clear a facemask; however, the VD of a facemask in preschool subjects). Adult-based data threshold under which the effect on LCI is difficult to measure. True effective VD is to quantify tissue N2 contribution to was no longer seen suggests that VD should affected by several factors: streaming of calculated FRC from the 1950s (51) should be minimized wherever possible within an gases within the facemask itself (61), the therefore not be extrapolated to preschool MBW system. amount of therapeutic putty used, and children. In fact, previous attempts to Increasing equipment-related VD leads variation in the VD displaced within the implement corrections based on these data to increased VD/VT, decreasing effective facemask during testing by face shape and in older school-aged subjects have been ventilation, and may trigger a compensatory operator pressure applied. As such, reported to be problematic (21). More change in breathing pattern and/or estimates of facemask VD should not be recent modeling work, based on a EELV. This is particularly relevant to incorporated into any corrections applied numeric two-compartment lung model, preschool-age subjects, as children with the to the pre–gas sampling point VD for suggested a small effect on measured smallest VT relative to fixed equipment- cumulative expired volume or FRC adult FRC values (1.8%, within the 5% related VD will be most affected. calculation. Instead, introduced facemask accuracy limit stipulated in the ERS/ATS Furthermore, changing relative VD per VD must be minimized by selection of the consensus statement), but a larger relative kilogram as a subject grows may influence smallest appropriate size that maintains effect on LCI (6.3%). The relative magnitude of error introduced worsened with increasing ventilation inhomogeneity and, of particular interest to preschool 30 MBW, with decreasing FRC (although this analysis used FRC values for a 10-year-old child and not preschool values per se) (54). However, preliminary in vivo studies 25 suggest the effect of tissue N2 increases with increasing lung volume and subject size, and as lung function worsens 20 (56). Although these findings are physiologically important, it remains to be determined whether correction for 15 tissue N2 would alter the interpretation of MBW results. 10 RECOMMENDATION: Relative Change in LCI from Baseline % 1. Until the magnitude of error introduced and validated correction equations are 5 available for inert gas diffusion across 0 246 – the alveolar capillary barrier, correction Vd/Weight(Kg) of MBW data for this effect is not Figure 2. Effect of increasing equipment-related VD on ventilation inhomogeneity. Data displayed recommended. are from 10 healthy adult subjects; lung clearance index (LCI) was calculated as the mean of triplicate tests across five VD values (standard, 150 ml, 1100 ml, 1150 ml, and 1200 ml). The D Equipment-related V change in LCI relative to baseline (i.e., standard VD) is expressed as a percentage (y-axis), and VD To reduce equipment-related effects on is expressed in terms of body weight (x-axis). The magnitude of effect observed on LCI suggests breathing pattern and end-expiratory a 10% increase in LCI for each 1-ml/kg increase in equipment-related VD. (Based on data contained lung volume (EELV), manufacturers of in Reference 59.)

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AMERICAN THORACIC SOCIETY DOCUMENTS face seal, and by applying therapeutic putty Environment for Testing acceptable; and additional safety appropriately (Figure 3). A detailed description of the desired precautions are necessary for preschool subjects, including, but not limited to, the RECOMMENDATIONS: skills and training of the preschool operator and environment for preschool lung need for constant adult supervision while 1. Manufacturers must minimize function testing was provided by the the child is in the laboratory. equipment-related VD. To ensure a ATS/ERS statement on pulmonary The operator has a crucial role to consistent approach across age ranges, function testing in preschool children (3), play to ensure the comfort level of the child. equipment-related VD should be kept but a number of important factors were Thelevelofdistractionmustbeenoughto below 2 ml/kg, as recommended in the stressed and are worth reinforcing: the take the child’s attention away from his or ERS/ATS consensus guidelines. importance of a “preschool-aged her breathing, and to minimize procedure- 2. Efforts to minimize VD within an MBW child–friendly” environment; the need related anxiety to achieve relaxed stable system must not adversely affect overall for the operator to engage, gain the trust tidal breathing. To expand further on resistance of the breathing circuit such of the child and encourage the child to this last aspect, the movie/show selected that breathing pattern is altered. participate in the test throughout the should encourage a calm and relaxed 3. MBW operators must minimize session without causing distress; adequate atmosphere and avoid sudden emotions facemask-associated VD by ensuring that allocation of time and patience by (e.g., excitement, singing, laughter, and/or the smallest appropriately sized operators trained in the techniques to fear). Interactive programs that encourage facemask is used, and by using help young children to perform at their talking or movement should be avoided. therapeutic putty within the facemask to best; ability to maintain equipment Respiratory function laboratories ensure that no obstruction to airflow and understand the procedure well enough should have a number of suitable occurs. toknowwhenaresultisorisnot choices from which the child can select, although the best choice may vary with the child, country, and culture. Preschool children should not have direct vision oftheonlinemeasurementsoftware to prevent “playing with signals” or manipulating visual feedback during the test. The preschool child must sit upright, handsbytheside,notelevatingtheir shoulders, and may require a stool to rest their feet. Positioning on a parent’slap mayhelpsettletheyoungerpreschool child but should not change this careful positioning of the child during testing. Familiarization visits for the child and parents to experience equipment, testing procedure, and environment used during testing are strongly recommended, and should also include practice with the test interface used. Two operators should be present during preschool testing: the first operator focuses on the child, the integrity of the interface seal, and maintaining adequate distraction by the movie/show to achieve a relaxed stable tidal breathing pattern. The second operator focuses on data collection and providing detailed ongoing feedback to the first operator on quality of data collected. Communication should occur in a discreet way and not disrupt the child’s distraction and Figure 3. Therapeutic putty use in facemask interfaces to reduce equipment-related VD. Additional relaxed breathing pattern. Adequate equipment-related VD introduced by a facemask assembly should be reduced as much as possible. time should be allowed for testing: an The smallest appropriately sized facemask should be selected. (A) Therapeutic putty application will be influenced by the presence of a flange to aid a leak-free seal when applied to the face during hour is recommended, especially in testing. In this case, putty is applied solely to reduce VD within the mask. (B) If no flange is present MBW-naive and/or younger preschool then putty also helps create the seal. A combination of different therapeutic putty consistencies may subjects, although shorter time periods be required to ensure that the putty maintains its shape and to prevent migration and outflow tract are feasible in experienced subjects. obstruction during testing. Detrimental effects of imposed limited e10 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

AMERICAN THORACIC SOCIETY DOCUMENTS time periods (e.g., 20 min for testing) have each test. Appropriate movie/show choice equipment, these cannot be directly been described (12, 62). is critical to the process. compared as each study differed across . 1 RECOMMENDATIONS: 5 Two operators should perform MBW several aspects, including ) variation in the testing in this age group, regardless of equipment setup between commercial and 1. The environment for preschool MBW interface choice. custom research equipment; 2) age ranges testing should be as child-friendly as tested; 3) variation in the definition of possible. The environment should be Preschool Test Feasibility acceptable data (i.e., two vs. three tests); 4) quiet, contain suitable preschool furniture The feasibility of MBW testing in preschool the duration allowed for the testing session and decoration, and accommodate adult children has been reported by several studies. (i.e., testing duration and whether MBW is supervision during testing. In the study by Aurora and colleagues, performed as the sole test or as part of a 2. Adequate time should be set aside for reporting a success rate of 79% across research protocol); and 5) the interface used testing in this age group, particularly for MBW-naive, 2- to 6-year-old children (16), (i.e., mouthpiece/nose-clip vs. facemask). those less than 4 years of age or who are feasibility was higher in healthy control Potential effects of these individual aspects on attending for the first time. An hour is subjects (84%) compared with subjects with feasibility are discussed in detail later in this recommended for initial testing. CF (75%), and a clear age-related effect was document. This variation in methodology 3. Familiarization visits are recommended observed. Feasibility was lowest in 2- to highlights the importance of implementing for the child and parents to experience 3-year-old children (50%), more than 80% the recommendations contained within this equipment, testing procedure, test in those above 3 years, and highest in technical standards document to standardize interface, and the environment used children 5–6 years of age (87%). the technique moving forward. during testing. The results of experience with Testing interface. The advantages and 4. Distraction during the assessment must commercial equipment (11, 12, 17, 59, disadvantages of the two testing interface be enough to take the child’sattention 63–66) are summarized in Table 4. Although choices in the preschool age range away from his/her breathing, the operator, it is encouraging to see comparable high (mouthpiece and nose-clip or facemask) and the immediate surroundings during rates of feasibility using commercial are summarized in Table 5. The use of a

Table 4. Published Preschool MBW Feasibility to Date, Using Commercial MBW Systems

No. of Age Tested MBW- No. of Acceptable Subjects Subjects Author (Year) Subjects (range, yr) naive (%) Interface Tests Required Attempted Successful (%)

Jensen 2014 (65)* CF 2.9–5.0 0 Facemask >2 tests 30 83 Benseler 2015 (59)* Healthy 2.8–5.9 Facemask 3 tests (successful on 24 83 – both equipment CF 3.3 5.9systems) 27 70 Robinson (64)* CF, wheeze 2.0–6.9 77 Facemask 3 tests 46 85 2 tests 46 91 77 Mouthpiece 3 tests 46 50 2 tests 46 63 Foong 2015 (66) Healthy 3.0–6.6 100 Mouthpiece >2 tests (first visit) 60 72 0 >2 tests (subsequent 19 86 visit) CF 2.6–6.6 100 Mouthpiece >2 tests (first visit) 78 67 0 >2 tests (subsequent 59 82 visit) Vilmann 2016 (63)* Healthy, 3–6 100 Mouthpiece >2 tests 66 89 asthmatic 3 tests 66 67 Downing 2016 (11)* Healthy, PCD, 2.1–5.9 100 Mouthpiece >2 tests within 30 min 116 73 CF, wheeze Yammine 2016 (12)† Asthmatic 3.1–6.7 100 Mouthpiece 3 tests within 20 min 62 24 2 tests within 20 min 62 60 Stanojevic 2017 (17)* Healthy, CF 2.5–5.9 100 Facemask >2 tests (first visit) 150 66 >2 tests (subsequent 150 89 visits)

Definition of abbreviations: CF = cystic fibrosis; MBW = multiple-breath washout; PCD = primary ciliary dyskinesia. *Modified from off-the-shelf equipment in an attempt to improve suitability for preschool testing. †Additional time restriction criteria of 20 minutes specified for total test session duration.

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Table 5. Advantages and Disadvantages Associated with Multiple-Breath Washout Test Interface Choice

Mouthpiece and Nose-Clip Facemask

Factors affecting ability to distract during testing Mouthpiece stimulation within the Avoids oral stimulation oral cavity (e.g., chewing) Pressure to face may distract if too great Need for reminders to maintain mouthpiece seal

Equipment-related VD Defined Difficult to define Seal (mouthpiece/mask) and risk of leak Subject determined Operator determined Impact of nasal airways Removed Unknown mouthpiece and nose-clip requires the child needs to be defined. Ultimately, interface preschool-specific acceptability criteria is to maintain a tight seal around the choice may depend on several factors, available. Special considerations are as mouthpiece to prevent leak, which may be including age and disease group being follows: 1) the minimal duration of difficult in this age group over the extended tested (i.e., familiarity with interface breathing stability before starting the test measurement periods required for MBW through regular medical treatments, should be shorter than is expected in testing. The mouthpiece may distract the e.g., use of facemasks with spacers and school-age and older subjects (30 s child, and trigger chewing, which may nebulized medications in young children), adapted to 3–5breaths);2) the acceptable present additional challenges to the operator outcomes being assessed (e.g., greater deviation in EELV at start of test should in maintaining a stable breathing pattern. If breathing stability is required for better reflect the inherent greater too large, the mouthpiece may also be concentration normalized phase III slope variability of EELV and VT in this age 3 uncomfortable. The use of a facemask [SnIII] analysis), and ability to factor in group; and ) operators should recognize provides some advantages, particularly practice sessions. Beneficial effects of the that sighs, swallows, and pauses may be because the operator is responsible for latter on both mouthpiece and facemask more frequently encountered compared maintaining an adequate seal. However, feasibility have been described (17, 66). with in older children, and tests should not facemasks add VD to the apparatus, which Ideally, the same interface should be used be rejected unless these have a resultant can be mitigated by the use of therapeutic for the duration of a study. However, this action of triggering trapped gas release or putty and may help facilitate a leak-free seal. may not be appropriate for longitudinal leak. Representative figures of acceptable Inserted putty should not obstruct the air studies spanning several years as children MBW tests typical of the preschool subject stream during breathing, which may be mayoutgrowthefacemask.Careful are shown in Figure 4. detected by the presence of box-shaped consideration of interface choice is Obtaining three technically acceptable fl – ow volume loops. The route of breathing necessary when planning and analyzing washout tests may be more challenging in fi in a facemask is not xed and nasal breathing the data of longitudinal studies where preschool children and may require multiple is possible. Adult data have demonstrated subjects switch interface within the study. attempts, with co-operation lost before this that nasal breathing may introduce target is reached. Work has focused on variability to the test result (64). Nasal and RECOMMENDATIONS: whether comparable information can be oral breathing have differing effects 1. Both a mouthpiece and nose-clip obtained from LCI values calculated from – on relative humidity and temperature of assembly and a facemask are supported two technically acceptable tests (68 73). expired gas, and may affect BTPS correction as interface choices for use in preschool- Firm recommendations cannot be made at accuracy (67). In addition, the degree of aged children. this stage, as further comparative data are nasal breathing encountered during testing is required for this approach evaluating the 2. At the present time these interfaces fi likely to vary within and between individuals must not be viewed as interchangeable sensitivity to detect bene cial effects of in the preschool age range. within this age range, and careful interventions. MBW operators are strongly Initial work directly comparing MBW consideration of interface choice is encouraged to obtain three tests, results performed with both interface options strongly recommended. with the aim of achieving at least two in the preschool age range suggests minimal technically acceptable tests to report differences overall (64); however, the Special considerations when reporting outcomes. Reported LCI and FRC relatively wide 95% limits of agreement preschool MBW data. Although technical values “based on the average of two values” observed suggest mask and mouthpiece MBW measurement acceptability criteria should be clearly stated. In the ATS/ERS should not be used interchangeably. The found in the ERS/ATS consensus statement 2007 preschool lung function statement, it same study suggested greater feasibility and are applicable to preschool testing, operators was recommended that if two tests were breathing pattern stability with a facemask may generally expect a more variable used to derive LCI, these should have interface, with a more pronounced breathing pattern in this age range. Hence, FRC values within 10% (where the highest difference observed in younger preschool we highlight the following aspects that will value is compared with the lower FRC subjects (64). If a facemask is used initially, require adaptation of previously published value) (3). This approach for MBW-based transition must occur as a subject ages, but criteria applicable to the preschool age FRC measurement accuracy had been the best approach and timing of transition range, until the required evidence for formal recommended in earlier lung volume e12 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

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A

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Vol. [ml], Flow 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Time (s)

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50 N2 [%]

0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 Time (s)

Figure 4. Typical breathing pattern observed in preschool subjects. (A–C) Sequential tests from the same test session, recorded using commercial N2-based multiple-breath washout equipment, in a preschool subject. At the top of each panel, real-time plots of tidal flow (black) and VT (red)aredisplayed;thebottomof each panel displays N2 concentration. These technically acceptable tests are representative of the variable breathing pattern encountered in preschool subjects and also contain examples of swallows (solid downward arrow) and sighs (solid upward arrow, no evidence of resultant trapped gas release).

fi measurement consensus documents, not not signi cantly alter LCI estimates (69). (e.g., moment ratios and SnIII analysis) specific to the preschool age range (74, 75). The formal FRC 10% acceptability criterion remains unclear. The increased variability Subsequent work has shown that when is no longer advocated in this age group for (e.g., for the second moment ratio, in formal 10% FRC reproducibility criteria LCI reporting, and requires physiological comparison with LCI) may be a factor were applied to preschool data from an FRC variability to be better defined affecting suitability for moment analysis fi experienced preschool MBW center it led to before speci c preschool criteria for (24). SnIII analysis requires clear 60% of data being excluded. This suggests FRC measurement accuracy can be visualization of the expirogram phase III that normal FRC variability within the recommended. slope, sufficient to estimate its magnitude, preschool age range is greater than The impact of reducing estimates to for both the first breath and two-thirds of this threshold and, importantly, also did the mean of two values for other indices breaths between 1.5 and 6.0 lung turnovers.

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Given this, greater tidal breathing stability variability in EELV and VT during co-operation time span of young children. during the test is needed (4). Tidal breath normal tidal breathing; and swallows, As in older age groups, this must phase III slopes (SIII) are often shorter in pauses, and sighs may occur more include real-time displays during both preschool children, compared with older frequently during the test. theprephaseandwashoutphaseof1)inert children (76). ERS/ATS consensus 2. Until definitive evidence is available for gas concentration versus time; 2) flow– document recommendations that SIII preschool children, MBW operators are volume loop (ideally with a display of the should be at least 50% of the expired strongly encouraged to perform three target VT rangeforthechild,typically fi – 3 volume have signi cant detrimental effects technically acceptable tests. Outcomes 8 12 ml/kg); )end-tidalCO2 (if CO2 on SnIII analysis feasibility in preschool derived from only two acceptable tests is measured) and respiratory rate to subjects, suggesting that the historical must be clearly identified when results detect hypo/hyperventilation or pediatric approach of being measured are reported in software. rebreathing; and 4) volume and flow- across 65–95% of the expired volume may 3. The previously recommended FRC 10% versus-time plots to assess breathing be more appropriate (77). For these acceptability criterion for LCI reporting pattern stability. Additional features reasons, the current approach of is no longer advocated in this age group. that will improve artifact detection include collating data from three technically autoscaling of the inert gas concentration acceptable tests for formal calculation may versus time plot during the washout provide a more robust estimate. Initial Recommendations for Commercial period, ideally with additional ability to efforts to explore this have reported a Software zoom in and out both during and after each statistically significant effect on measured Recommendations for commercial software test. The utility of incentive feedback has SnIII outcomes, based on two rather than development and use for both yet to be established in preschool MBW. three tests, in preschool but not older manufacturers and operators are Automated start and stop functions during pediatric subjects (73, 78). summarized in Table 6. Quality control testing may be attractive to the operator

RECOMMENDATIONS: should extend beyond equipment but are actively discouraged until formal performance to include accurate real-time validation of effectiveness is clearly 1. The approach to individual test and biological feedback to the operator described.

overall test session acceptability in during testing. Real-time software RECOMMENDATIONS: preschool children should be adapted to recommendations are applicable to all age reflect differences in comparison with groups,butareofincreasingimportance 1. Software must enable adequate visual older subjects: preschool children to the operators working with preschool quality control of the volume, flow, and require a shorter duration of pretest subjects to allow efficient use of test inert tracer gases for the entire duration breathing stability; may have greater time, given the limited concentration and of each test.

Table 6. Recommendations for Commercial Software Development and Use for Manufacturers and Operators

Manufacturer Directed Operator Directed d Real-time biological feedback data must be displayed during d Close inspection of display for artifact during each test must be both prephase and washout phases of each test. performed by a dedicated operator. Further review after each test is d Additional operator ability to zoom in and out both during and completed. Rejection of tests containing artifact after each test to detect subtle artifact d Real-time inert gas concentration plot against time must be displayed. d Autoscaling of display during the washout to facilitate artifact detection d Real-time flow–volume loop must be displayed for each breath d Close inspection of whether the VT size is appropriate for the subject (i.e., flow vs. volume plot for each breath), referenced to a (typically defined as 8–12 ml/kg) must be performed. A clearly visible specified number of previous breaths (e.g., at least 5 breaths). phase III slope of the expirogram is supportive of this. d Display of target VT range appropriate for the subject d Flow–volume loop display useful in preschool testing to detect d Real-time display of expirogram for each breath during the obstruction of the facemask outflow tract, with any therapeutic putty washout portion of each test used to reduce equipment-related VD d d End-tidal CO2 should be displayed to assess for End-tidal CO2 should remain within the normal range (typically hyper/hypoventilation. defined as 4–6%) through both the prephase (or wash-in) and d Calculation and display of respiratory rate during each test washout portions of each test. d Single real-time VT (both inspiratory and expiratory) vs. time d Evidence of breathing pattern and EELV stability must be present must be displayed to monitor breathing pattern and stability of before starting each test (defined as present for 3–5 breaths). end-expiratory lung volume. d Manual start and stop options of the washout portion of each d Until automated start and stop functions of testing have been test must be provided. validated, manual option to start and stop each test must be used.

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2. Software quality control cannot be upper limit of normal from older age confirmation of competence to collect automated until clear evidence-based groups is not recommended. good-quality data should be part of this thresholds are available. The available collated reference process (84). Numbers recommended for 3. Incentive software is not recommended data (79) were based on data collected spirometry (e.g., 300 subjects) reflect the in this age range. by a custom-built respiratory mass characteristics of spirometric indices (85) spectrometer–based MBW system using and should not be extrapolated to MBW, SF6 as the inert tracer gas. The described where the minimum number has yet to be Reference Data for Preschool relationship between LCI and height likely defined. Collaborative efforts to achieve MBW exists for all inert gases and systems in early robust reference data are strongly life (81), but reference ranges should not be recommended. For many years, reference values for MBW extrapolated to other MBW systems and RECOMMENDATIONS: indices, such as LCI, were assumed to be across different inert gases (82, 83). independent of age. Collated data from Extrapolation could lead to misdiagnosis 1. Available reference data from older infancy to adolescence demonstrate an of abnormal ventilation distribution, subjects must not be extrapolated to the inverse relationship between LCI and and inappropriate tracking of disease preschool age range. height, most pronounced in the first 3 years progression over time, especially in 2. Collaborative efforts to achieve robust preschool-specific reference data are of life, with plateauing of the upper limit of preschool children (83). strongly recommended. normal from 6 years of age (79) (Figure 5). Pooling currently available data in 3. Until robust device-specific reference The reasons for elevated LCI values in healthy control subjects (e.g., from studies equations are published for commercial younger healthy children have not been listed in Table 4) is challenging because of systems, research groups must ensure fully explored, but are most likely many aspects of the methodological that studies collect an appropriately variation discussed in the section PRESCHOOL multifactorial: ongoing lung and chest wall matched control group. development and dysanaptic growth TEST FEASIBILITY (above). Future pooled between airway (bronchial) and acinar reference population data used to derive the “ ” MBW Use in Preschool (parenchymal) volume (80) such that the normal range for individual commercial Interventional Research conducting airway space is larger in relation or research MBW systems must align Studies to lung volume, which increases respiratory methodology to address these issues, rate and dead space per minute ventilation; contain sufficient numbers from the MBW holds exciting promise as an end use of sedation and supine testing position population being tested (i.e., preschool), point for early intervention strategies in in infancy; and relatively larger equipment- and report outcome measures collected CF (14, 15), and was used as the primary related VD in younger subjects during using standardized protocols, equipment, outcome in an international multicenter testing. Given this, extrapolation of an and settings. Training of operators and study in 6- to 11-year-olds (84). To date,

A B 5 Female 12 Male

4 10

L 3 MBW 8 ULN LCI

FRC 2

6 1 LLN 0 4 50 100 150 200 50 100 150 200 Height cm Height cm Figure 5. Changes in multiple-breath washout (MBW) indices—lung clearance index (LCI; A) and FRC (B)—across the pediatric age range. Data taken from a cohort of 497 subjects (ranging in age from infancy to 19 yr) tested on 659 occasions using custom-built research MBW equipment and sulfur hexafluoride as the inert tracer gas of interest. (A) The solid line denotes the predicted (50th centile) LCI for height, and the dashed lines denote the upper limit of normal (ULN; 97.5th centile) and lower limit of normal (LLN; 2.5th centile). The typical height range of a preschool child is 75 to 125 cm. These data must be viewed as inert gas– and equipment-specific. (Reproduced by permission from Reference 79. This material has not been reviewed by European Respiratory Society before release; therefore the European Respiratory Society may not be responsible for any errors, omissions, or inaccuracies, or for any consequences arising therefrom, in the content.)

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AMERICAN THORACIC SOCIETY DOCUMENTS only one small single-center CF remain poorly understood (14, 15, 88). before formal commercial release. It remains clinical trial has used LCI as an end point In addition, the relationship between unclear whether a specificinertgaschoiceis in the preschool age range (86). This improvement in LCI and other surrogate warranted in this age range. Until there is fi study was able to demonstrate strong end points such as FEV1 or rate of FEV1 evidence of signi cant detrimental effects feasibility and ability of MBW outcomes decline remains unclear. More information or lack of validation with one particular to detect a treatment effect despite a small is urgently needed in this area, including choice, no firm recommendations for a sample size (N = 25). Subsequent larger, comprehensive, longitudinal studies in specificchoicecanbemadeandanumber multicenter trials of hypertonic saline health and disease to elucidate how MBW of choices will be supported. A choice of (SHIP and SHIP-CT studies: clinical trial outcomes change over time within interface is also supported based on current registration numbers NCT02378467 and individuals in the preschool age range. Data evidence and experience. Efforts to optimize NCT02950883, respectively; www. outlining variability over time have started feasibility and breathing pattern stability in clinicaltrials.gov) and a cystic fibrosis to emerge. Aurora and colleagues described younger children with facemasks must be transmembrane conductance regulator a mean (95% confidence interval) within- accompanied by the development of effective (CFTR) modulator (Vertex: clinical trial subject change of 0.0 (–0.2 to 0.2) units in strategies to define optimal training regimens registration number NCT02797132) have healthy subjects measured at two time and timing of transition to a mouthpiece and commenced since. Experience to date, points (preschool and early school age), nose-clip interface, so that detrimental effects within the working group, has which were on average 3.7 (range, 1.3–6.6) on breathing stability and MBW outcomes highlighted the value of careful and years apart (89). Stanojevic and colleagues are minimized at later ages. The latter in rigorous training, a subsequent observed the same stability in healthy particular may be best accomplished using a certification process targeting the age preschool subjects measured over several coordinated effort to perform comparison being tested in the study, central time points across a 12-month period. studies across multiple sites and equipment overreading, and ongoing quality control. LCI within a comparison preschool CF to ensure results obtained are generalizable. This approach has achieved high rates of cohort increased by 0.4 units/year in Future work must establish clear successful testing and acceptable data contrast to FEV1, which did not change objective criteria for an acceptable test and both in the preschool age range (17) and (17). Pooling of data from treatment overall test session in this age group, to school-aged children (84). A sequential studies within specific disease groups may minimize subjective assessment. These efforts approach to training with initial experience offer opportunities to accelerate this to standardize reporting have commenced built in older volunteers, before preschool- process, and the use of MBW in children (91), but require future work, especially in specific training, has been beneficial. with CF undergoing exacerbation treatment preschool children. The medium term aim Standardization of equipment setup and is an example of the benefits of this must be to provide an accurate tool, which testing protocol across sites within a single approach (90). can be feasibly incorporated into routine study is critical for all age groups, but clinical care. Regional regulatory approval becomes more important in preschool (e.g., U.S. Food and Drug Administration children because of the extra demands Future Work and Conclusions approved) for devices fulfilling the criteria placed on the system and the operators outlined in this document, with for testing in this age range. Appropriate Important areas for future work in this demonstrated strong feasibility for testing timelines for site training and certification age group are summarized in Table 2. across the preschool age group, will be an must be integrated into studies. Testing Replicating the strong feasibility of research- essential step in that process. should be performed before any procedures based equipment, while maintaining its Future technological advances may offer that require active cooperation as it is easier sensitivity as an outcome measure in opportunity for optimizing MBW device to “wind up” than “wind down” the child pediatric obstructive lung disease (16, 86), is design and must be encouraged. An example and it has been reported that deep inhalation the challenge faced by emerging commercial of one such area is advances in mainstream may alter bronchial tone (87). Interpretation equipment. Many of the commercial systems O2 analysis, which may one day negate of results from these ongoing preschool available today were designed for older the need for sidestream O2 analysis and MBW interventional studies will need subjects, and need extensive testing, and in adjustments for associated sample flow rate to consider the unknown aspects of some cases modifications, before they are (92). The development of mainstream standardization outlined in this document suitable for use in preschool children. As analysis for not just one but all gases (e.g., physiological considerations of inert such, the flexibility to conduct future studies measured also offers the opportunity to gases, testing interface, reference data, and may be inhibited because of limitations reduce analyzer response time further (e.g., minimal clinically important differences). within the commercial software. Custom to 10 ms in this case). This is important research-based software, developed for given the increased susceptibility of research-built MBW equipment, will also preschool MBW to sources of technical error. Minimal Clinically Important play a key supportive role in this progress. Current recommendations (,2ml/kg)for Difference Commercial software developers must equipment-related VD target alignment with recognize that modifications may have a the recommendations of older age groups, To date the minimal clinically important significant impact on MBW outcomes, and but further minimization through targeted difference in preschool subjects for LCI or ensure that the full impact of software design and better appreciation of streaming any other MBW index, as well as respective changes, for a range of patient demographics, within bacterial filters may facilitate meeting intrasubject and intersubject variability, is evaluated and transparently documented the less than 1-ml/kg effective VD advocated e16 American Journal of Respiratory and Critical Care Medicine Volume 197 Number 5 | March 1 2018

AMERICAN THORACIC SOCIETY DOCUMENTS for infant systems (93). Whether new extend to MBW outcomes beyond FRC standardization and validation in this age facemasks that prevent nasal breathing alone, as FRC accuracy cannot be range and will increase the utility of the test would be beneficial to address issues raised in extrapolated to other outcomes (e.g., LCI). in the future. n this document needs to be determined. Although many challenges remain, MBW Device design must also incorporate the need testing in preschool children already provides for infection control, an increasingly an exciting approach to detect and monitor Acknowledgment: The authors thank Mr. Jeremy Wolfensberger (Division of important area in conditions such as CF, early lung disease. Implementation of the Respiratory Medicine, Department of where MBW interest is currently greatest. recommendations contained within this Pediatrics, University of Bern, Bern, Validation approaches should aim to technical standards document is essential for Switzerland) for the use of Figure 1.

This official technical statement was prepared by an ad hoc subcommittee of the ATS Assembly on Pediatrics.

Members of the subcommittee are as FELIX RATJEN, M.D., PH.D. advisory committee for Vertex. A.H. served follows: as a consultant for Celtaxys; and served MARGARET ROSENFELD, M.D., M.P.H. on an advisory committee for Boehringer PAUL D. ROBINSON,M.B.Ch.B.,PH.D. (Chair) FLORIAN SINGER, M.D., PH.D. Ingelheim, Chesi, Innovision Ap, and Vertex. PAUL AURORA, M.B. B.S., PH.D. SANJA STANOJEVIC,PH.D. P.L. received personal fees from Gilead, Novartis, Polyphor, Roche, Schwabe, STEPHANIE D. DAVIS, M.D. PADMAJA SUBBARAO, M.D., M.Sc. Vertex, Vifor, and Zambon. C.M. served MONIKA GAPPA, M.D., PH.D. as a consultant for Proteostasis, Vertex, PER M. GUSTAFSSON, M.D. Author Disclosures: P.D.R. served on an Gilead, and AbbVie; received research advisory committee and received research support from Proteostasis, Parion Sciences, GRAHAM L. HALL,PH.D. support from Vertex. S.D.D. served on an and Vertex; and served on an advisory ALEX HORSLEY, M.B. Ch.B., PH.D. advisory committee for Vertex and Parion committee and as a speaker for Gilead. RENEE JENSEN, R.R.T. Sciences; served as a consultant for F.R. served as a consultant for Aerovanc, Vertex and Eli Lilly; served on an advisory Aptalis, Bayer, Genentech, Gilead, PHILIPP LATZIN, M.D., PH.D. committee for Parion Sciences; served as a Insmed, Novartis, Roche, Savara, and SOOKY LUM,PH.D. speaker for Parion Sciences and ABComm; Vertex; and received research support CARLOS MILLA, M.D. received research support from Parion from Ecomedics and Vertex. P.A., P.M.G., Sciences; and is supported by an educational R.J., S.L., K.G.N., J.E.P., K.A.R., M.R., KIM G. NIELSEN, M.D. grant from Gilead. M.G. conducted research F.S., S.S., and P.S. reported no JESSICA E. PITTMAN, M.D. with equipment provided by ndd Medical relationships with relevant commercial KATHRYN A. RAMSEY,PH.D. Technologies. G.L.H. served on an interests.

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