Reproducibility of spirometry during cystic fibrosis pulmonary exacerbations

Objectives: To compare the within day variation of spirometry between hospital admission, discharge, and outpatient follow up among children with cystic fibrosis (CF) hospitalized for a pulmonary exacerbation.

Hypothesis: Within day variation of spirometry will be greater at hospital admission than at hospital discharge or outpatient follow up.

Methods: We performed a retrospective review of spirometry data for all patients with CF >or=6 years old admitted to our pediatric CF center for a pulmonary exacerbation in 2004 or 2005. For patients who had previously performed spirometry successfully, measurements were used from one admission only during 2004-2005 if the spirometry occurred within 3 days of hospital admission, 3 days of discharge, or at a follow up clinic visit when well. We compared the within day coefficients of variation (CV) for FVC, FEV(1), and FEF(25-75) between time points using the Wilcoxon signed rank-test. We also determined the change in spirometry that is likely to be beyond measurement variability during inpatient treatment of a pulmonary exacerbation.

Results: Spirometry data were available from 40 subjects at admission and follow up and 35 at hospital discharge. There was no significant difference in CV at admission, discharge, and follow up for FVC, FEV(1), or FEF(25-75). The mean (SD) CV was 3.1% (2.7) for FVC, 3.2% (2.1) for FEV(1), and 9.7% (7.0) for FEF(25-75) at admission, 2.8% (2.2) for FVC, 3.1% (2.1) for FEV(1), and 8.1% (6.7) for FEF(25-75) at discharge, and 2.7% (1.7) for FVC, 2.8% (2.0) for FEV(1), and 8.4% (7.8) for FEF(25-75) at follow up. These are similar to previous reports of outpatients with CF. The improvement in spirometry that exceeded measurement variability for our cohort was 80 ml for FVC, 70 ml for FEV(1), and 220 ml/sec for FEF(25-75).

Conclusions: The presence of an acute pulmonary exacerbation in children and adolescents with CF does not substantially contribute to the within day variation in spirometry. Within day variation of spirometry for children with CF during pulmonary exacerbations is similar to previously reported values from clinically stable CF patients.