Nitrogen multiple breath washout test for infants with cystic fibrosis

Abstract

Multiple breath washout test (MBW) with lung clearance index (LCI) as a main outcome parameter has proven to be a valuable research tool in patients with cystic fibrosis (CF) [1, 2]. Moreover, there is growing evidence of its relevance in routine clinical practice [3]. Nevertheless, some technical limitations remain that hamper its widespread use. While most of the MBW data in infants have been acquired via sulfur hexafluoride washout (SF 6-MBW), the nitrogen variant (N 2-MBW) is recommended by the European Cystic Fibrosis Society Clinical Trial Network (ECFS-CTN) for older children. However, this methodological discrepancy may limit long-term follow-up of cystic fibrosis patients because N 2and SF 6-MBW cannot be used interchangeably. In infants, the N 2-MBW has not been fully investigated to date. We report our data regarding safety, feasibility and repeatability of N 2-MBW in cystic fibrosis infants. Between January 2015 and January 2017, we performed lung function testing in 35 infants aged 6.7-25.2 months (median 14.7) with classical form of cystic fibrosis. Testing was performed in patients without any signs of acute respiratory infection for at least 14 days. Quiet sleep was induced by administering chloral hydrate 80-100 mg•kg −1 per rectum. The patients were placed in a supine position with their head and neck in a neutral position, and a Rendell-Baker face mask Nr. 1 or 2 (selected to keep the instrument dead space under 2 mL•kg −1) was tightly sealed around the mouth and nose. At first, N 2-MBW was performed using the Exhalyzer D device (Ecomedics, Duernten, Switzerland) with the Spiroware 3.2.0 software, following all the relevant recommendations [4, 5]. When finished, at least 120 s of medical air breathing followed (normalisation of breath pattern, nitrogen back wash-in). Afterwards, SF 6-MBW was performed using the same device and software within a subgroup of 10 patients, who were tested after March 2016 (SF 6-MBW became available in our centre); their anthropometric parameters and age were not significantly different from those of the whole study group. Both measurements were performed in fixed order within the same sedation period and without changing the body and face mask position. The technical acceptability of trials was assessed by a physician with ECFS-CTN certification in this method and adhered to the standard operating procedure for N 2-MBW [5] modified for infants and SF 6-MBW. Both tests were repeated at least three times to obtain a coefficient of variation (CV) lower than 10%. Pulse rate and haemoglobin oxygen saturation were continuously monitored during MBW measurements and until full consciousness was regained. A pair-wise t-test was used to compare results from SF 6and N 2-MBW in individual patients with both measurements available (n=8). Patient's characteristics between the N 2-MBW and SF 6-MBW group were compared by the t-test. The reliability of N 2-MBW was assessed using estimates of intraclass correlation (ICC). Coefficient of repeatability was calculated as follows: 1.96×...

Difference between SF6 and N2 multiple breath washout kinetics is due to N2 back diffusion and error in N2 offset

“…We observed that N 2 -LCI was 8% higher in HC, similar to the 10% difference observed by Jensen et al Other investigators have not reported differences using a common FRC, but we found that this increases the observed differences in LCI. A more recent study measuring LCI in infants with CF under sedation showed higher FRC and LCI values and lower tidal volumes with the use of N 2 -MBW when compared with SF 6 -MBW (15).…”

Cystic fibrosis year in review 2018, part 1

“…The technical feasibility was 100% with the new device, but software systems reduced comparability of the new device configuration in measurements of FRC . Another study showed feasibility, safety, and reproducibility of N 2 MBW in CF infants, as well as possible improved performance compared with SF 6 MBW . Both of these studies lead to better ability to perform MBW in our youngest patients.…”

“…94 Another study showed feasibility, safety, and reproducibility of N 2 MBW in CF infants, as well as possible improved performance compared with SF 6 MBW. 95 Both of these studies lead to better ability to perform MBW in our youngest patients.…”

End‐expiratory lung volume remains stable during N 2 MBW in healthy sleeping infants

“…The lung clearance index (LCI) from the MBW test has been recently endorsed as a primary outcome measure in CF clinical trials (Kent et al, 2014). The impact of inert gas choice remains of great interest (Guglani et al, 2018;Gustafsson, Bengtsson, Lindblad, & Robinson, 2017) and nitrogen-based (N 2 ) MBW using 100% oxygen (O 2 ) continues to be advocated for this infant age group (Koucky, Skalicka, & Pohunek, 2018). Our work has focused on defining the physiological impact of 100% O 2 exposure during MBW in this age group.…”

“…These were not observed during SF 6 MBW where O 2 exposure was kept constant at 21%. Exposure to 100% O 2 led to a transient significant reduction in tidal volume (V T ), minute ventilation (V′ E ), and "respiratory drive" (mean inspiratory flow; V T in/Tin) with a concomitant increase in end-tidal CO 2 , while respiratory rate was unchanged (Koucky et al, 2018). A significant rise of the end-expiratory lung volume (EELV, i.e., FRC) by a mean of 19 ml (≈10% relative) occurred based on the cumulative difference between inspiratory and expiratory tidal volumes (V T in -V T ex) measured by the ultrasonic flow meter over the course of the N 2 washout phase.…”