FeNO 350 mL/s: Unlocking the Small Airways to Achieve Clinical Remission in Severe Asthma-A Pilot Study

Background: Several studies focused on the importance of managing small airways disease in the treatment of severe asthma, whose improvement can improve respiratory symptoms, lung function, and airways inflammation, potentially reaching the objective of clinical remission. Methods: Twenty-five patients with severe asthma and without bronchiectasis were enrolled. They were started on biological therapies with Omalizumab, Dupilumab, Benralizumab or Mepolizumab. Follow-up evaluations were conducted at baseline (T0) and after one year of biological therapy (T1). Assessments included clinical evaluations, spirometry, questionnaires, and inflammatory markers. Results: Predictive analysis identified baseline FeNO 350 mL/s levels as a significant predictor of clinical remission in both univariable and multivariable analysis. Higher FeNO 350 mL/s levels at T0 were associated with an increased likelihood of achieving remission (p = 0.012). The optimal cutoff value for FeNO 350 mL/s was determined to be 18 ppb, based on the Younden Index. Conclusions: Following patients with severe asthma on biological therapy for one year, FeNO 350 mL/s could be used as a predictive factor of clinical remission, highlighting its importance as inflammatory marker not only in small airways disease, but also in predicting clinical remission in severe asthmatic patients.