Exhaled Nitric Oxide Levels during Acute Asthma Exacerbation

Objectives: Fractional exhaled nitric oxide (FE_NO) has been shown in laboratory settings and trials of patients with stable asthma to correlate with the degree of airway inflammation. The authors hypothesized that the technique of measuring FE_NO would be reproducible in the setting of acute asthma in the emergency department (ED) and that the FE_NO results during ED visits would potentially predict disposition, predict relapse following discharge, and correlate with the National Institutes of Health (NIH) asthma severity scale and peak expiratory flow measurements. Methods: The authors prospectively measured FE_NO in a convenience sample of ED patients with acute exacerbations of asthma, both at the earliest possible opportunity and then one hour later. Each assessment point included triplicate measurements to assess reproducibility. The authors also performed spirometry and classified asthma severity using the NIH asthma severity scale. Discharged patients were contacted in 72 hours to determine whether their asthma had relapsed. Results: The authors discontinued the trial (n= 53) after a planned interim analysis demonstrated reproducibility (coefficient of variation, 15%) substantially worse than our a priori threshold for precision (4%). There was no association between FE_NO response and corresponding changes in spirometry or clinical scores. Areas under the receiver operating characteristic curves for the prediction of hospitalization and relapse were poor (0.579 and 0.713, respectively). Conclusions: FE_NO measurements in ED patients with acute asthma exacerbations were poorly reproducible and did not correlate with standard measures of asthma severity. These results suggest that using existing technology, FE_NO is not a useful marker for assessing severity, response to treatment, or disposition of acute asthmatic patients in the ED.