Pulmonology | 2021
Implementing nitrogen multiple breath washout as a clinical tool - A feasibility study.
Abstract
The multiple-breath inert gas washout (MBW) test involves recording an inert tracer gas being cleared from the lungs during normal tidal breathing. In nitrogen (N2) MBW resident nitrogen is washed out by inhaling 100% oxygen. MBW allows us to calculate the lung clearance index (LCI), defined as the number of lung turnovers required to washout an inert gas to 1/40th of its initial concentration. 3 It offers complementary information to standard lung function tests, such as spirometry The procedure is strongly dependent on skilled operators and a relaxed testing environment is key to obtaining good quality measurements. Operator training and certification in performance of the MBW measurement is imperative to achieving high-quality data, and standardization of LCI is part of an ongoing collaborative, multicentre process. Aim: to assess the feasibility of N2MBW in a paediatric lung function laboratory in children with different clinical conditions [Cystic Fibrosis (CF), primary ciliary dyskinesia (PCD) and healthy controls]. School-aged children with a confirmed diagnosis of CF or PCD were recruited from a Paediatric Pulmonology clinic in a tertiary-care hospital, and healthy controls from the community, throughout December/2018-November/2019. Patients were clinically stable at inclusion and the study procedures were performed during the patients’ routine clinic visits. Height and weight were measured prior to the lung function assessments, and BMI z scores standardized using WHO reference values. Exhalyzer D and the associated software Spiroware version 3.1 (EcoMedics AG, Duernten, Switzerland) were utilized for the N2MBW measurements and calculation of the N2MBW indices. The means of the N2MBW indices from intentionally three and at least two technically acceptable measurements performed at each test occasion were reported in absolute values. Prior to implementing this technique in our setting, three operators completed a European standardization and certification process for measuring LCI through N2MBW with a commercial device (specific training and sharing of data for central over-reading). Static and dynamic lung volumes were measured by body plethismography and spirometry (Jaeger MasterScreen Body, CareFusion, Hoechberg, Germany) after the N2MBW procedure. Absolute values for static lung volumes and z-scores for dynamic lung volumes and flows were recorded and performed according to the ERS/ATS standards. Patient characteristics were presented by medians (ranges) or numbers and percentages of total. Patients with CF and PCD were grouped for comparison with healthy controls. Group differences were analysed using the independent t-test, Mann Whitney U-test, and Chi-squared test as appropriate; p< 0.05 was accepted as statistically significant. Data analyses were performed using Microsoft Excel for Office 365 MSO and SPSS 24.0. The study was approved by a local ethics community (Comiss~ ao de Etica para a Investigaç~ ao Clínica). Informed consent for participation was obtained. During the study period 34 children were assessed, five were excluded due to invalid MBW readings and two successfully repeated the procedure in a different testing session. The success rate for performing N2MBW for the first time was 75% (22 out of 29). Additionally, all healthy controls were naïve to lung function testing, and one was unable to perform spirometry properly. We analysed data from 29 children: ten CF, six PCD and thirteen healthy controls (Table 1). There were no differences between patients and healthy children regarding gender, age, or BMI. The diseased group had higher LCI [10.8 (7.6; 15.3) vs 6.9 (6.5; 7.5)], and lower FEV1 [-0.8(-2.8; 0.4) vs. 0.7(-0.9; 1.8)] and MMEF [-1.0 (-2.6; 0.3) vs. 0.03 (-0.5; 2.4)] when compared to healthy controls (p < 0.001). Executing MBW took 28 (16; 76) minutes [patient group 29 (16; 76) minutes; healthy controls 22 (16; 53 min], and it was attempted for 5 (3; 15) trials in each testing session (Table 2). For nine individuals (four healthy controls, two CF and three PCD), only two technically acceptable trials were achieved.