Expired nitric oxide and airway obstruction in asthma patients with an acute exacerbation

Expired nitric oxide (eNO) is a marker of airway inflammation that is increased in asthma. The present study was undertaken to examine the clinical utility of eNO as an aid in the assessment of asthma in the emergency department (ED). Fifty-two adult patients with acute asthma, 53 age- and sex-matched controls, and eight patients with stable asthma were enrolled. Subjects performed spirometry, their eosinophil counts and serum total IgE were measured, and a sample of mixed VC expirate was collected for measurement of NO. Mixed expired NO was 8.2 +/- 0.5 ppb in controls, 8.8 +/- 1.5 ppb in patients with stable asthma, and 15.0 +/- 1.0 ppb in patients with acute asthma. A significant difference in eNO was observed in patients with acute asthma and controls (p < 0.001). Twenty-three of the 52 patients with acute asthma versus two of 53 controls had an eNO >/= 15 ppb (p < 0.001). Expired NO concentration correlated with FEV1% (r = -0.42, p < 0.001) and with the peripheral blood eosinophil count (r = 0.34, p < 0.001) in the group of 60 patients with acute and stable asthma. The sensitivity of eNO > 10 ppb and eosinophilia (> 200 cells/microliter) was 90% in predicting airway obstruction (FEV1/FVC < 0. 8). No relationship of eNO was found to serum IgE, self- reported smoking, or glucocorticoid use. Measurement of eNO is a promising clinical tool for assessing acute asthma.