Simplified quality control criteria for the multiple breath washout technique

Abstract

Background: Multiple breath washout (MBW) is increasingly used in the clinical assessment of patients with cystic fibrosis (CF). However, guidelines for real-time quality control of MBW measurements are lacking.

Objectives: We aimed to develop simple quality control criteria for prospective assessment of nitrogen MBW measurements and to validate these criteria through retrospective analysis.

Methods: A system was developed to grade MBW quality whereby A, B, and C grades indicate acceptable trials, D grade indicates questionable trials with unstable breathing pattern, and F grade denotes trials that are technically not acceptable. We retrospectively assessed 52 clinically obtained MBW test occasions (134 trials) from children in two centres (Bern: patients with CF; Hannover: patients with CF after lung transplantation) using our simplified quality control criteria. We assessed success rate of MBW, comparison of MBW outcomes (lung clearance index (LCI)) reported before and after quality control, and interrater agreement of three experienced reviewers (KR, JC, BF).

Results: While all test occasions were accepted in clinics only 69% of test occasions were accepted after quality control. From the 134 trials, 68% were acceptable (A-C grade), 19% were questionable (D grade), and 13% were rejected (F grade). There was a significant difference in LCI between accepted (median LCI 8.9 (6.4-17.8)) and rejected test occasions (13 (7.3-19) p= 0.01). Interrater agreement between reviewers was good (85%, κ =0.6).

Conclusion: Not performing quality control of clinical MBW data may result in overestimation of LCI. We recommend prospective MBW quality control in the clinical setting.