4.
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 guidelines11,13-15. 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 et al. and Saunders et
al 11 14 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 studies15,17, 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
review13. 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 level18.
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.
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 trials11 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 statement11. 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 N2MBW 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.