Wednesday, June 3, 2020

Exhaled nitric oxide analysis

Case:  23 year female with a long history of asthma is admitted to ICU with exacerbation of her symptoms. Despite standard therapies, she deteriorated and required intubation. Pulmonary service inquired about the availability of exhaled nitric oxide (eNO) analysis. What is the clinical application of exhaled nitric oxide (eNO) analysis?

Answer: It helps to suggest glucocorticoid responsiveness in Asthma

Nitric oxide (NO) has various functions in the bronchial tree. It regulates vascular and bronchial tone, facilitates the coordinated beating of ciliated epithelial cells, and acts as an important neurotransmitter for non-adrenergic, non-cholinergic neurons that run in the bronchial wall. NO can be measured in exhaled gas as the fraction of exhaled NO (FENO).

One of its major applications is found in asthmatic patients who usually have higher than normal levels of FENO.
  • FENO <25 ppb in asthmatics despite persistent symptoms suggests other etiologies for their symptoms, and suggests that inhaled glucocorticoid treatment may not be necessary
  • FENO >50 ppb even with atypical symptoms suggests glucocorticoid responsiveness



1. Blitzer ML, Loh E, Roddy MA, et al. Endothelium-derived nitric oxide regulates systemic and pulmonary vascular resistance during acute hypoxia in humans. J Am Coll Cardiol 1996; 28:591.

2. Dweik RA, Boggs PB, Erzurum SC, et al. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FENO) for clinical applications. Am J Respir Crit Care Med 2011; 184:602.

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