Children with asthma often have normal spirometry despite significant disease. The pathology of the small airways in asthma may be assessed using Multiple Breath Washout (MBW) and calculating the Lung Clearance Index (LCI). There are only few studies using MBW in children with asthma and existing data regarding bronchodilator effect are contradictory. The aim of the present pilot study was to compare LCI in asthma and controls and assess the effect of salbutamol in children with asthma on the LCI.

Unselected patients with a diagnosis of asthma visiting the outpatient department of our hospital between 04-2010 and 03-2011 were recruited and compared to a healthy control group. MBW was performed as inert gas MBW using sulfurhexafluorid (SF₆) as the tracer gas. Clinical data were documented and spirometry and MBW (EasyOne Pro, MBW module, NDD Switzerland) were performed before and after the use of salbutamol (200–400 μg). Healthy controls performed baseline MBW only.

32 children diagnosed with asthma (4.7–17.4 years) and 42 controls (5.3–20.8) were included in the analysis. LCI differed between patients and controls, with a mean LCI (SD) of 6.48 (0.48) and 6.21 (0.38) (P = 0.008). Use of salbutamol had no significant effect on LCI for the group.

These pilot data show that clinically stable asthma patients and controls both have a LCI in the normal range. However, in patients the LCI is significantly higher indicating that MBW may have a role in assessing small airways disease in asthma.