Using index of ventilation to assess response to treatment for acute pulmonary exacerbation in children with cystic fibrosis.

Background: The use of alternative more sensitive measures has become a focus of research in CF. The utility of indexes of ventilation, Lung Clearance Index (LCI) and peak aerobic capacity (peak VO(2)), were studied as assessment tools in gauging response to intravenous (IV) therapy in acute pulmonary exacerbation, in comparison to the more commonly used index of forced expiratory volume in 1 sec (FEV(1)). The utility of a previously published clinical score was further explored.
Methods: Patients aged 8-18 years admitted for IV antibiotic treatment of a pulmonary exacerbation were recruited. Spirometry, plethysmography, multiple breath nitrogen washout, exercise testing, and Cystic Fibrosis Clinical Score (CFCS) were performed on admission and prior to discharge.
Results: Twenty-eight patients were recruited, with a mean (range) age of 13.7 (8; 17) years, 16 female and 12 male. Mean (range) admission FEV(1) was 61.4 (28; 92)% predicted, or z-score -3.09 (-6.15; -0.52), FVC 83.0 (38; 120)% predicted, or z-score -1.71 (-5.66; -1.17), and Shwachman-Kulczycki 68.9 (50; 90). FEV(1) increased by 7.0% (P < 0.01) from admission to discharge. Mean (range) admission LCI, 10.10 (6.87; 14.83), decreased by 3.8% (P = 0.03). Mean (range) admission peak VO(2) (ml/kg/min), 31.2 (23.4; 45.4), increased on discharge by 6.6% (P < 0.01). Proposed clinical thresholds, based on the available variability data, highlighted the heterogeneity of response in lung function tests. Mean (range) admission CFCS, 26.5 (19; 39), decreased to 19.9 (13; 31) on discharge, a 25.2% improvement (P < 0.01). CFCS demonstrated improvement in 27 of 28 patients. Changes in peak VO(2) (r = -0.50, P = 0.02) and LCI (r = 0.48, P = 0.01) correlated with CFCS change.
Conclusions: In children with mild-to-moderate CF, whilst statistically significant improvement in both LCI and peak VO(2) were seen, heterogeneity of response was evident. The most consistent improvement was seen in CFCS. Correlation of LCI and peak VO(2) with change in clinical score (CFCS) was seen. The full clinical significance of these changes in LCI and peak VO(2) needs to be evaluated further with additional variability data. The CFCS may be useful in the assessment of response to treatment in CF but requires formal validation.