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\begin{document}

\title{Multiple breath washout quality control in the clinical setting}



\author[1]{Bettina Frauchiger}%
\author[2]{Julia Carlens}%
\author[3]{Andreas Herger}%
\author[3]{Alexander Moeller}%
\author[1]{Philipp Latzin}%
\author[1]{Kathryn Ramsey}%
\affil[1]{Inselspital University Hospital Bern}%
\affil[2]{Medizinische Hochschule Hannover}%
\affil[3]{University Children's Hospital Zurich}%


\vspace{-1em}



  
  \date{June 14, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Background: Multiple breath washout (MBW) is increasingly used in the
clinical assessment of patients with cystic fibrosis (CF). Guidelines
for MBW quality control (QC) were developed primarily for retrospective
assessment and central overreading. We assessed whether real-time QC of
MBW data during the measurement improves test acceptability in the
clinical setting. Methods: We implemented standardized real-time QC and
reporting of MBW data at the time of the measurement in the clinical
pediatric lung function laboratory in Bern, Switzerland in children with
CF aged 4-18 years. We assessed MBW test acceptability before (31 tests;
89 trials) and after (32 tests; 97 trials) implementation of real-time
QC and compared agreement between reviewers. Further, we assessed the
implementation of real-time QC at a secondary center in Zurich,
Switzerland. Results: Before implementation of real-time QC in Bern,
only 68\% of clinical MBW tests were deemed acceptable following
retrospective QC by an experienced reviewer. After implementation of
real-time QC, MBW test acceptability improved to 84\% in Bern. In
Zurich, after implementation of real-time QC, test acceptability
improved from 50\% to 90\%. Further, the agreement between MBW operators
and an experienced reviewer for test acceptability was 97\% in Bern and
100\% in Zurich. Conclusion: Real-time QC of MBW data at the time of
measurement is feasible in the clinical setting and results in improved
test acceptability.%
\end{abstract}%



\sloppy


\textbf{Multiple breath washout quality control in the clinical setting}

Bettina S. Frauchiger\textsuperscript{1*}, Julia
Carlens\textsuperscript{1,2*}, Andreas Herger\textsuperscript{3},
Alexander Moeller \textsuperscript{3}, Philipp
Latzin\textsuperscript{1}, Kathryn A. Ramsey\textsuperscript{1\#}

1. Pediatric Respiratory Medicine, Department of Pediatrics,
Inselspital, Bern University Hospital, University of Bern,
Freiburgstrasse 8, 3010 Bern, Switzerland+

2. Clinic for Paediatric Pneumology, Allergology and Neonatology,
Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany

3. Division of Respiratory Medicine and Children's Research Center,
University Children's Hospital Zurich, Zurich, Switzerland +

+ Institutions where research was mainly conducted

\subsubsection*{* Co-first authors: Authors contributed
equally}

{\label{co-first-authors-authors-contributed-equally}}

\textsuperscript{\#} Corresponding author:

Kathryn Ramsey

Inselspital, Bern University Hospital,

Freiburgstrasse 8, Bern 3010 Bern, Switzerland

Email: Kathryn.ramsey@extern.insel.ch

Funding: This project was funded by the Swiss National Science
Foundation, Grant Nr. PZ00P3\_168173 (Latzin) / 1; 32003B\_182719
(Ramsey)

Keywords: Multiple breath washout, lung clearance index, quality
control, cystic fibrosis, children

Running head: Quality control for multiple breath washout

Wordcount (without abstract): 3270 words

Abstract: 220 words

Author contributions: BF, JC, PL, AM, and KR were responsible for the
conception and design of this study. BF, JC, and KR drafted the quality
control guidelines and the structured implementation in clinical
routine. Data acquisition was conducted by BF and AH. BF, JC, AM, PL,
and KR were responsible for data interpretation. Statistical analysis
was conducted by BF and KR. BF, JC, AM, PL, and KR drafted the
manuscript and all authors revised and approved the manuscript for
intellectual content before submission.

\subsubsection*{Abstract}

{\label{abstract}}

Background: Multiple breath washout (MBW) is increasingly used in the
clinical assessment of patients with cystic fibrosis (CF). Guidelines
for MBW quality control (QC) were developed primarily for retrospective
assessment and central overreading. We assessed whether real-time QC of
MBW data during the measurement improves test acceptability in the
clinical setting.

Methods: We implemented standardized real-time QC and reporting of MBW
data at the time of the measurement in the clinical pediatric lung
function laboratory in Bern, Switzerland in children with CF aged 4-18
years. We assessed MBW test acceptability before (31 tests; 89 trials)
and after (32 tests; 97 trials) implementation of real-time QC and
compared agreement between reviewers. Further, we assessed the
implementation of real-time QC at a secondary center in Zurich,
Switzerland.

Results: Before implementation of real-time QC in Bern, only 68\% of
clinical MBW tests were deemed acceptable following retrospective QC by
an experienced reviewer. After implementation of real-time QC, MBW test
acceptability improved to 84\% in Bern. In Zurich, after implementation
of real-time QC, test acceptability improved from 50\% to 90\%. Further,
the agreement between MBW operators and an experienced reviewer for test
acceptability was 97\% in Bern and 100\% in Zurich.

Conclusion: Real-time QC of MBW data at the time of measurement is
feasible in the clinical setting and results in improved test
acceptability.

\par\null

\subsubsection*{1. Introduction}

{\label{introduction}}

The lung clearance index (LCI) derived from the multiple breath washout
technique (MBW) is sensitive to detect early lung disease in patients
with cystic fibrosis (CF) \textsuperscript{1-4}. With the availability
of commercial MBW devices, LCI is increasingly being used as an outcome
in routine clinical surveillance \textsuperscript{5-10}. While MBW
testing requires minimal cooperation from the subject, an acceptable
test requires relaxed tidal breathing and a leak-free
system\textsuperscript{11}, which can be challenging in young children
and individuals with respiratory disease\textsuperscript{12}. Besides,
prospective quality control (QC) of MBW measurements can be challenging
in the busy clinical setting.

Quality control guidelines for MBW focus primarily on retrospective
analysis and central overreading of MBW measurements by experienced
users for research studies and clinical
trials\textsuperscript{11,13-15}. The 2013 European Respiratory Society
(ERS) and American Thoracic Society (ATS) consensus statement for inert
gas washout measurements proposed initial recommendations for testing
procedure and technical acceptability criteria \textsuperscript{11}.
Further to this, ATS published additional guidelines for the preschool
age group \textsuperscript{14}. Jensen \emph{et al.} proposed
comprehensive guidelines for retrospective quality control of MBW
measurements, which involved both qualitative and quantitative criteria
for trial grading and acceptability\textsuperscript{13}. These
guidelines were further implemented in a standardized MBW training and
quality control platform for central overreading in clinical
trials\textsuperscript{15}. However, for LCI to be used as a clinical
outcome, prospective reporting of acceptability and test results is
required for clinical decision making.

Therefore, we aimed to implement prospective, real-time quality control
of MBW measurements in the clinical pediatric lung function laboratory
in Bern, Switzerland. The first aim was to evaluate the acceptability of
clinical MBW measurements in children with CF before and after the
implementation of real-time quality control. The second aim was to
assess the implementation of real-time quality control of MBW
measurements in a pediatric lung function laboratory with less
experience in MBW testing, Zurich, Switzerland. The third aim was to
evaluate agreement in MBW test acceptability between the operator and a
retrospective reviewer.

\subsection*{2. Methods}

{\label{methods}}

\emph{2.1 Development of MBW quality control criteria}

The quality control criteria used in this study was based on the ATS/ERS
consensus statement guidelines, ATS pre-school MBW technical statement,
and the publications by Jensen \emph{et al} and Saunders \emph{et
al.}\textsuperscript{11,13-15}. We used these guidelines to create a
simplified matrix for qualitative assessment of clinical Nitrogen
(N\textsubscript{2}) MBW measurements that can be applied at the time of
the measurement and did not require any further retrospective
assessment.

Our quality control criteria are presented in Table 1 and details of how
our criteria differ from the ERS/ATS consensus statement are provided in
Supplemental Table E1. Detailed instructions on how to apply the
guidelines are presented in the online supplemental. An A grade
represents a perfect trial with relaxed, regular tidal breathing
throughout the measurement, a B grade represents a good quality trial
with only minimal deviations, and a C grade represents an acceptable
trial with moderate deviations but no highly abnormal breaths during the
pre-phase or start of washout. A, B and C grade trials are considered
acceptable for outcome reporting. D grade represents trials with
questionable quality due to variable breathing patterns, abnormal
breaths, or evidence for hypo- or hyper-ventilation. D grade trials have
no signs of leak and satisfy both the start and end of test criteria.
Generally, D grade trials should be rejected and not used for reporting,
however, sometimes the deviations in tidal breathing in a D trial do not
significantly impact the primary outcomes. Therefore, we propose that D
grade trials can be accepted if the primary outcomes (LCI and FRC) are
within 10\% of an acceptable trial (A, B or C grade). An F grade
represents trials that need to be rejected due to not meeting the
technical acceptability criteria for MBW: 1) Start of test criteria not
met (last three breaths of pre-phase N\textsubscript{2}-concentration
with normalized N\textsubscript{2} concentration [?] 77\%); 2) End of test
criteria not met (three consecutive tidal breaths with normalized
N\textsubscript{2} concentration \textless{} 2.5\%; 3) No evidence of
leaks (for detailed instruction see online supplemental).

The overall test occasion is classified as acceptable when (i) at least
two trials are graded as acceptable (A, B or C), or (ii) one trial was
graded as acceptable (A, B, or C) and one trial was graded as
questionable (D) given that both FRC and LCI are within 10\% of the A-C
grade trial when there are only two trials or 10\% of the median when
there are three or more trials for this test occasion. A test occasion
with only D trials should be rejected. We used the overall test
repeatability criteria described in the consensus document (i.e. FRC
variability within 25\%)\textsuperscript{11}. MBW outcomes from
acceptable and repeatable test occasions are reported as the mean from
all acceptable trials.

2.2 MBW data collection and study population

{\label{mbw-data-collection-and-study-population}}

The N\textsubscript{2}MBW measurements were collected using the
Exhalyzer D device (Ecomedics, Duernten, Switzerland) with Spiroware
software (version 3.2.1) and were performed according to international
guidelines \textsuperscript{11} in both centers. We approached all
pediatric patients with CF attending their regular three monthly
outpatient clinic visits aged 4 to 18 years. Approval was obtained from
the local ethics committee in Bern. Patients and caregivers gave
informed consent.

\subsection*{\texorpdfstring{\emph{2.3 Test acceptability before
implementation of real-time MBW quality control in
Bern}}{2.3 Test acceptability before implementation of real-time MBW quality control in Bern}}

{\label{test-acceptability-before-implementation-of-real-time-mbw-quality-control-in-bern}}

Before implementation of real-time MBW quality control criteria into
clinical routine in our centre, MBW operators were trained in data
collection and general test acceptability. However, due to time
restrictions, they were not required to perform a detailed assessment of
test quality during the measurement. They also did not routinely mark
trial classification on the lung function reports. To assess the quality
of these MBW measurements, 31 clinic visits from children with CF aged
five to 18 years were evaluated. The visits were randomly selected by an
independent person not involved in this study and only one visit per
patient was included in the analysis. Retrospective quality control was
performed by an experienced reviewer who was involved in the development
of the criteria and was blinded to any test comments by the MBW
operator. The reviewer graded each trial individually and then assessed
overall test acceptability.

\subsection*{\texorpdfstring{\emph{2.4 Test acceptability after
implementation of real-time MBW quality control in
Bern}}{2.4 Test acceptability after implementation of real-time MBW quality control in Bern}}

{\label{test-acceptability-after-implementation-of-real-time-mbw-quality-control-in-bern}}

To implement real-time quality control of MBW measurements, operators in
our center received instruction on how to perform quality control. A
printed copy of the quality control criteria matrix was provided and
operators were given a presentation on how to use the matrix, grade
individual trials, determine test acceptability and repeatability, and
report outcomes (detailed information provided in online supplement).
All MBW operators were required to perform real-time quality control of
each MBW measurement. The operators reported a grade for each trial and
provided a standardized comment regarding the acceptability of the test
occasion in the clinical report (example provided in the online
supplement).

To assess the quality of MBW measurements after implementation of
real-time quality control in routine clinical testing, 32 clinic visits
from the same population of children with CF were evaluated. The visits
were randomly selected by an independent person not involved in this
study and only one visit per child was assessed. The experienced
reviewer performed retrospective quality control of these measurements
while being blinded to the real-time quality control assessment of the
operator.

\emph{2.5 Assessment of real-time MBW quality control in secondary
centre in Zurich}

To validate our findings, we implemented real-time MBW quality control
in a centre (Zurich, Switzerland) with less experience in MBW
methodology. We first assessed MBW measurements from a random subset of
34 clinical visits from pediatric patients with CF attending their
routine care in Zurich, Switzerland. The MBW operators were then
instructed on how to use the quality control matrix and given access to
the supplementary teaching material (see online supplemental). Mandatory
real-time MBW quality control and reporting of test acceptability was
implemented for all measurements. We then retrospectively assessed test
acceptability and agreement between the operator and reviewer in a
random subset of 30 MBW measurements.

\emph{2.6 Outcomes before and after real-time quality control}

To determine whether performing real-time quality control influenced
outcomes, we compared mean outcomes (LCI; FRC) and variability
(coefficient of variation; (CV)) before and after implementing real-time
quality control. Further, we assessed the impact on MBW outcomes of
including D grade trials within 10\% variability of good quality trials
as proposed in this manuscript.

\subsection*{\texorpdfstring{\emph{2.7 Data
analysis}}{2.7 Data analysis}}

{\label{data-analysis}}

For this study, we examined MBW test acceptability before and after
implementation of real-time quality control in the clinical setting.
Before the implementation of real-time quality control, as primary
outcome, we compared test acceptability reported in the clinical reports
generated by MBW operators to those reported following retrospective
quality control by the experienced reviewer (BF). After the
implementation of real-time quality control, as primary outcome, we
compared test acceptability and trial acceptability reported at the time
of the measurement by MBW operators to those reported following
retrospective quality control by the experienced reviewer (BF). As a
secondary outcome, we assessed the agreement in test acceptability and
trial grading between the MBW operator and an experienced reviewer.
Agreement was assessed using kappa statistics. We also compared MBW
outcomes (mean and within-test coefficient of variation for FRC and LCI)
reported by the operator and reviewer using unpaired t-tests. All
statistical analysis was performed using Stata 16.0 (StataCorp
2019)\textsuperscript{16}.

\subsection*{3. Results}

{\label{results}}

\emph{3.1 Study population}

The demographic characteristics of study participants from both centers
are summarized in Table 2. The population in Zurich was on average
younger, however, the age range of patients was similar between both
centers. Anthropometric characteristics (height, weight, BMI, and age)
and MBW outcomes (LCI and FRC) were well matched between the two study
populations.

\emph{3.2 MBW test and trial acceptability before implementing real-time
quality control}

MBW test acceptability results are summarized in Table 3. In Bern,
before implementing real-time quality control, 89 MBW trials from 31
test occasions were evaluated. After retrospective analysis of quality
control by the reviewer, 68\% of test occasions were deemed acceptable.
In terms of MBW trials, 51 (57\%) were accepted and 38 (43\%) were
rejected following retrospective quality control by the reviewer. The
reasons for trial rejection (details provided in Table 4) included F
grade trials whereby the technical acceptability criteria were not met,
D grade trials with irregular breathing patterns, and good quality
trials (A-C grade) from test occasions without at least two acceptable
trials.

In Zurich, before implementing real-time quality control, 97 MBW trials
from 34 test occasions were evaluated. After retrospective quality
control by the reviewer, only 50\% of the test occasions were deemed
acceptable. In terms of MBW trials, 47 (49\%) were accepted and 50
(51\%) were rejected following retrospective quality control by the
reviewer. The reasons for trial exclusion (details provided in Table 4)
were similar to Bern.

\emph{3.3 MBW test and trial acceptability after implementing real-time
quality control}

Test acceptability after implementing real-time MBW quality control is
summarized in Table 3. In Bern, 97 trials from 32 MBW test occasions
were evaluated. Test acceptability improved from 68\% to 84\% and trial
acceptability improved from 57\% (51/89) to 70\% (68/97) (Table 5). In
Zurich, 91 trials from 30 MBW test occasions were evaluated after
implementing real-time quality control. Test acceptability improved from
50\% (17/34) to 90\% (27/30), trial acceptability improved from 49\%
(47/97) to 74\% (67/91) (Table 5).

\emph{3.4 Agreement between MBW operator and reviewer after implementing
real-time quality control}

After implementing real-time quality control, the agreement between
operator and reviewer was high in both centers. For test acceptability
agreement was 97\% (\selectlanguage{polish}ĸ \selectlanguage{english}= 0.9, p \textless{} 0.001) in Bern and 100\% (\selectlanguage{polish}ĸ \selectlanguage{english}=
1.0, p \textless{} 0.001) in Zurich. In Bern, only one test occasion was
rejected by the reviewer but not by the operator. The remaining four
test occasions rejected by the reviewer were also rejected by the
operator. In Zurich, all test occasions rejected by the reviewer were
also rejected by the operator.

For trial grading, agreement was 68\% (\selectlanguage{polish}ĸ \selectlanguage{english}= 0.6, p \textless{} 0.001) in
Bern and 73\% (\selectlanguage{polish}ĸ \selectlanguage{english}= 0.6, p \textless{} 0.001) in Zurich. In Bern, the
operators were able to recognize all technically invalid trials (F
grade). All F grade trials consisting of leaks were identified by the
operator. The only trials in which the end of test criteria was not met
were trials that were prematurely terminated by the operator. All the
trials evaluated satisfied the start of test criteria, which meant that
operators were consistently waiting enough time between trials. Three
trials were given a C grade by the operator and a D grade by the
reviewer due to irregular breathing pattern. However, these trials were
then excluded by both as not being accompanied by a second good quality
trial. Only one trial with a D grade was rejected by the reviewer but
not by the operator. In Zurich, only one F grade trial that did not meet
the end of test criteria was not recognized by the operator. Leaks were
all correctly identified by the operator. As in Bern all trials
satisfied the start of test criteria. One trial was given a D grade by
the reviewer and a C grade by the operator, however, both were rejected
for final reporting as not being accompanied by a second good quality
trial.

\emph{3.5 MBW outcomes before and after quality control}

We determined whether performing quality control significantly
influenced MBW results in our subset of measurements. We found no
differences in LCI or FRC mean values or variability reported by the MBW
operator compared with the reviewer before and after real-time quality
control (Supplemental Table E2 and E3). Further, we assessed the impact
of accepting D grade trials with LCI and FRC values within 10\% of an
acceptable trial on MBW outcomes and variability. We found no
significant differences in LCI, FRC, or outcome variability (LCI/FRC
coefficient of variation) between tests with and without accepting these
D trials (Supplemental Table E4).

\par\null

\subsection*{4. Discussion}

{\label{discussion}}

We assessed the quality of MBW measurements collected in clinical
routine before and after implementing mandatory real-time quality
control in two centers. We provided the MBW operators with a simplified
quality control matrix according to current guidelines and assessed
whether real-time quality control of MBW data during the measurement
improves test acceptability in routine clinical testing. Following
implementation of real-time quality control, acceptability of MBW
measurements improved from 68 to 84\% in Bern and from 50\% to 90\% in
the validation center Zurich, and resulted in excellent agreement
between the operator and reviewer.

Implementing mandatory real-time quality control improved overall test
acceptability and the ability of MBW operators to recognize and perform
good quality MBW measurements in routine clinical testing. Before
implementation of real-time quality control criteria, operators reported
outcomes to the clinicians with trials that should have been rejected
according to current quality control
guidelines\textsuperscript{11,13-15}. After implementing mandatory
real-time quality control and providing the simplified guidelines in
Bern, operators were able to correctly identify all technically not
acceptable trials. These findings were validated in a center with less
experience in MBW measurements (Zurich). These results indicate that
performing standardized real-time quality control is feasible in the
clinical setting, improves overall test acceptability, and results in
good agreement between reviewer and operator.

Our quality control guidelines are a simplified version of the current
MBW consensus guidelines, preschool technical standards, and quality
control guidelines by Jensen \emph{et al.} and \emph{Saunders et al}
\textsuperscript{11} \textsuperscript{14} \textsuperscript{13,15}. Due
to the complexity and time consuming nature of the MBW test, there has
been a focus on the need for detailed retrospective quality control and
central over-reading by highly experienced MBW researchers. While
central over-reading is a suitable approach for large, multi-centre
research studies\textsuperscript{15,17}, clinical MBW testing requires
immediate reporting of outcomes. Therefore, real-time quality control by
the operator is the only way to ensure that good quality MBW outcomes
are used for clinical interpretation. Our quality control criteria
(Table 1) provide simplified guidelines for MBW trial grading, trial
acceptability, and test acceptability. They can be applied at the time
of the measurement to allow immediate reporting of MBW data in clinics.
To maintain high quality MBW data in the clinical setting we suggest
that centres implement regular training sessions with operators, provide
updates of recent literature in the field, and perform regular
over-reading of random subsets of MBW measurements in order to provide
feedback to the operators.

We found that systematic quality control of MBW measurements by an
experienced reviewer did not lead to differences in mean LCI or FRC
values compared with values reported without quality control. These
findings are similar to those reported by Jensen et al, who found no
differences in mean LCI values following qualitative and quantitative
review\textsuperscript{13}. However, while both studies reported no
significant differences in outcomes on a population level, reporting
outcomes from technically not acceptable MBW trials can impact the
outcomes of a test occasion on an individual level\textsuperscript{18}.
In the clinical setting, longitudinal changes in MBW outcomes from one
visit to the next are likely to influence treatment decisions.
Therefore, it is essential to ensure that only data from good quality
MBW trials are reported\emph{.}

In the clinical setting, trials with highly irregular breathing pattern
(D grade) but meeting technical acceptability criteria are a frequent
challenge. Especially in younger children, where individual attention
may be limited and time restricted in busy outpatient clinics,
collecting three immaculate trials can be challenging. We, therefore,
decided to follow a pragmatic approach and include them for outcome
reporting if at least one good quality trial (A, B or C trial) within
the same test occasion was available and LCI and FRC are within 10\% of
this acceptable trial. The consensus statement suggests repeatability of
FRC to be within 25\% of the median FRC of technically acceptable
trials\textsuperscript{11} and states that trials exceeding those limits
should prompt further investigation. We did not find an influence on MBW
outcomes and test variability when including these D grade trials and
variability was substantially lower than the limits proposed by the
consensus statement\textsuperscript{11}. However, these criteria need to
be validated in a larger dataset.

There are some limitations to our quality control criteria. Trial
grading is based on qualitative criteria for breathing pattern that are
inherently subjective. Users need to have familiarity with the MBW test
to differentiate between minimally and moderately variable breathing
pattern. However, many of these subjective criteria will only influence
whether a trial is graded as either A, B or C, all of which are
technically acceptable trials. Our criteria could have been simplified
further to only include acceptable, questionable, or rejected trial
grading, however, MBW operators stated that it was beneficial to be able
to recognize what constitutes a technically perfect trial and understand
which deviations can still be accepted. Further, our quality control
criteria are only applicable to N\textsubscript{2}MBW measurements. This
study was performed using Ecomedics equipment and Spiroware 3.2.1
software whereby flow-volume loops, nitrogen, oxygen, and carbon dioxide
signals are visible during and after the measurement. It is unclear how
easily these criteria can be applied to data collected in other devices,
software, and alternative tracer gases.

Conclusion

Real-time quality control of MBW data at the time of the measurement is
feasible in the clinical setting and results in improved test
acceptability with excellent agreement between MBW operators and
experienced reviewers. Our quality control criteria provide simplified
guidelines for MBW trial grading, trial acceptability, test
acceptability, and outcome reporting that can be applied even in centers
with less experience in MBW methodology. Applying these criteria by MBW
operators at the time of the measurement ensures that only good quality
MBW outcomes are reported to the clinician.

\textbf{Acknowledgments}

The authors also thank to all our patients and families for allowing
their MBW data to be used for research. The authors thank to all our lab
technicians for collecting daily MBW measurements, especially Mrs.
L\selectlanguage{ngerman}üscher, Mrs. Vessaz, Mrs. Krattinger and Mrs. Wirz in Bern as well as
Mrs. Böhringer, Mrs. König, Mrs. Noser and Mr. Vogt in Zurich.

\textbf{Conflicts of Interest}

Dr. Latzin: personal fees from Vertex, Novartis, Roche, Polyphor, Vifor,
Gilead, Schwabe, Zambon, Santhera, grants from Vertex, all outside this
work. All other authors have no conflicts of interest.



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