Time between multiple breath nitrogen washout (MBNW) tests: Is duration of washout enough across childhood?

Abstract

Background: Recommendations state that up to twice the washout time may be required between multiple breath washout (MBW) tests to avoid detrimental effects on FRC and LCI. Current commercial Nitrogen MBW (MBNW) equipment employ a “lockout” period between tests, whilst stabilisation of breathing prior to starting the next washout portion further lengthens duration of nitrogen re-accumulation between tests. Aims and Objectives: To investigate for evidence of insufficient wash-in (FRC or LCI decline) occurs if a “lockout” period equal to previous washout period duration is used from preschool age range onwards. Methods: Retrospective analysis of clinical MBW tests at a single tertiary paediatric centre using commercial MBNW equipment (Ecomedics Exhalyser D, Switzerland). Lockout period set to duration of washout on previous test. Consecutive pairs of technically acceptable MBNW tests analysed for FRC or LCI difference using paired t-test and Bland Altman analysis. If three successive tests available, test 1-3 difference also analysed. Secondary analysis of effect across preschool (2-6 yrs), school age (7-12 yrs) and adolescence (13-18 yrs). Results: Data from 80 children (30 preschool, 30 school age, 20 adolescent subjects) included to date, mean (SD) FRC 1523 (827) mL and LCI 8.08 (2.38), generating 137 test pairs and 55 triplets. No significant differences observed between FRC or LCI test pairs or across tests 1-3 for entire cohort or in each age group examined. Conclusion: No evidence of insufficient wash-in was observed. Clinical application of a lockout period of previous washout duration can be recommended across the paediatric age range in commercial MBNW equipment.