Introduction Lung clearance index (LCI) can detect small airways disease in asthma; however there is no published LCI data collected during acute exacerbation. We aimed to investigate LCI in asthmatic children requiring oral corticosteroids and admission to hospital.

Methods Children were recruited from acute medical wards. We tested children once they did not require oxygen or >2 hourly salbutamol. Admission details were extracted from medical notes. Multiple breath washout (MBW) was performed with sulphur hexafluoride and the Innocor photoacoustic gas analyser. Spirometry complied with ATS/ERS standards and was performed using the Easyone spirometer. MBW and spirometry were performed shortly before and 15 min after children's clinically prescribed salbutamol. Paired t tests and Pearson correlation coefficients were used in the analysis.

Results Nine children aged 6.4–13.6 years were recruited. Testing began on average 201 min after each child's last salbutamol. LCI was calculated for eight children, the ninth was excluded due to variable FRC. Pre bronchodilator mean (SD) LCI was 8.6 (1.8), but was only abnormal (=7.4) in 5/8 children; following bronchodilator mean (SD) LCI was 8.1 (1.2). Mean (SD) FEV₁ z-score was −3.5 (1.6) and was abnormal (<−1.96) in 6/8 children; post bronchodilator FEV₁ z-score was −2.9 (1.4). Mean LCI correlated with FEV₁ z-score before and after bronchodilator (r=−0.80, p=0.017 and r=−0.76, p=0.030). In patients with abnormal LCI there was a significant improvement after salbutamol; with a mean difference of −0.918, p=0.018. In this group FEV₁ z-score improved by a mean of 0.802, p=0.051. Although overall both measures improved, the degrees of improvement in LCI and FEV₁ did not correlate (r=−0.361, p=0.550). Two patients who both had abnormal pre bronchodilator LCI (mean 11.1) returned 8–10 weeks later, both had normal LCI (mean 6.9).

Conclusions LCI is abnormal in children during exacerbation of asthma. Abnormal LCI improves following bronchodilator, but changes do not correlate with changes in FEV₁. This suggests variable bronchodilator response throughout the airway. Recruitment for this study is ongoing.

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Abstract P78 Figure 1

Post bronchodilator change in FEV₁ and LCI in five patients with abnormal LCI.