Fractioned exhaled nitric oxide (FE(NO)) is not a sufficiently reliable test for monitoring asthma in pregnancy.

It has been reported that fractioned exhaled nitric oxide (FENO) can be used for monitoring airway inflammation and for asthma management but conclusions drawn by different researchers are controversial. The aim of our study was to evaluate the clinical usefulness of FENO assessment for monitoring asthma during pregnancy. We monitored 72 pregnant asthmatics aged 18-38years (Me=29 years) who underwent monthly investigations including: the level of asthma control according to GINA (Global Initiative for Asthma), the occurrence of exacerbations, ACT (Asthma Control Test), as well as FENO and spirometry measurements. In 50 women, during all visits, asthma was well-controlled. In the remaining 22 women, asthma was periodically uncontrolled. FENO measured at the beginning of the study did not show significant correlation with retrospectively evaluated asthma severity (r=0.07; p=0.97). An analysis of data collected during all 254 visits showed that FENO correlated significantly but weakly with ACT scores (r=0.25; p=0.0004) and FEV1 (r=0.21; p=0.0014). FENO at consecutive visits in women with well-controlled asthma (N=50) showed large variability expressed by median coefficient of variation (CV)=32.0% (Min 2.4%, Max 121.9%). This concerned both: atopic and nonatopic groups (35.5%; and 26.7%, respectively). Large FENO variability (35.5%) was also found in a subgroup of women (N=11) with ACT=25 constantly throughout the study. FENO measured at visits when women temporarily lost control of asthma (N=22; 38 visits), showed an increasing tendency (64.2 ppb; 9.5 ppb-188.3 ppb), but did not differ significantly (p=0.13) from measurements taken at visits during which asthma was well-controlled (27.6 ppb; 6.2 ppb-103.4 ppb). The comparison of FENO in consecutive months of pregnancy in women who had well-controlled asthma did not show significant differences in FENO values during the time of observation. The assessment of asthma during pregnancy by means of monitoring FENO is of limited practical value due to this parameter's considerable intrasubject variability, regardless of the degree of asthma control.

[The long-term variability of FeNO in pregnant asthmatic women with controlled asthma]. / Dlugoterminowa zmiennosc stezenia tlenku azotu w wydychanympowietrzu (FeNO) w astmie kontrolowanej u kobiet w ciazy.

INTRODUCTION: Fractional exhaled nitric oxide (FeNO) is considered as a useful, noninvasive marker of airway inflammation in asthma and allergic rhinitis. It has also been suggested that anti-inflammatory treatment guided by monitoring of exhaled NO could improve overall asthma control. However, long-term intra-subject variability of this parameter as well as the rate of its change, which can be clinically significant, have not been established yet. The aim of our study was to assess the long-term variability of FeNO in pregnant asthmatic women with controlled asthma. MATERIAL AND METHODS: Pregnant, non-smoking women with asthma were recruited between 3 and 6 months of gestation. Exhaled nitric oxide (FeNO) spirometric parameters were measured, and the asthma control test (ACT) was completed during monthly visits up to delivery. The data of 26 subjects with well-controlled asthma during pregnancy (ACT values within the range 20-25, normal spirometric parameters, stable treatment) were analysed. The variability of FeNO values was assessed using the variation coefficient CV (standard deviation x 100%/arithmetic mean). RESULTS: The median level of FeNO coefficient of variation (CV) was: 33.8% (range 11.3 to 121.9) in all subjects with well-controlled asthma during pregnancy. There were no statistically significant differences in FeNO variability between groups of patients who had at least one measurement of FeNO higher than 50ppb (39%; 11.8-121.9%) and those with all FeNO values below 50ppb (29.9%; 11.3-71.8%), as well as between atopic (35.7%; 11.8-121.9%) and nonatopic (24.2%; 11.3-71.8%) pregnant asthmatics (p = 0.95 and 0.11, respectively). CONCLUSIONS: High long-term variability of fractional exhaled nitric oxide values revealed in pregnant women with well-controlled asthma indicates that changes in this parameter should be interpreted with caution while being used for asthma treatment monitoring.