Offline Exhaled Nitric Oxide in Emergency Department and Subsequent Acute Asthma Control

Abstract

Background. Few studies have evaluated exhaled NO measurement during acute asthma. Objectives. To evaluate exhaled NO fraction (FE_NO) and peak expiratory flow (PEF) time-courses during acute asthma treatment (β 2-agonist plus systemic steroid) and to assess whether FE_NO time-course predicts subsequent asthma control. Methods. Sixty-five asthmatic patients (mean ± SD, 34 ± 10 years) were prospectively enrolled in three Emergency Departments. Results. Sixteen patients were excluded (failure of offline FE_NO measurement at 100 mL/s [FE_{NO 0.1}], n = 4, and early discharge). The 49 remaining patients performed FE_{NO 0.1} and PEF on admission, at the 2nd (H2) and 6th hour (H6). Follow-up using an Asthma Control Diary was obtained in 27 of 49 patients, whether they were hospitalized (n = 9) or discharged (n = 18). All but 2 patients had elevated FE_NO on admission (median [interquartile], 49 [26–78] ppb). Unlike PEF, mean FE_{NO 0.1} of our sample was not significantly modified by treatment. No significant relationship was evidenced between exhaled NO and PEF variations. The variation of FE_{NO 0.1} [H0 minus H6] was different in patients who were hospitalized (decrease of 8 ± 20 ppb) versus discharged (increase of 5 ± 20 ppb, p = 0.04). This variation of FE_{NO 0.1} was correlated with the Diary score (control of subsequent week), an initial increase in FE_{NO 0.1} being associated with better asthma control. Nevertheless, neither exhaled NO nor PEFR were good predictors of asthma control. Conclusions. An increase in FE_NO is observed in almost all patients with acute asthma, and its subsequent increase within 6 hours is associated with a better degree of asthma control in the subsequent week.

Keywords:

• asthma attack
• Asthma Control Diary score
• emergency department
• offline exhaled nitric oxide
• peak expiratory flow