Safety of Sputum Induction in Interstitial Lung Disease

Introduction: Sputum induction (SI) is a safe and effective technique to study airway inflammation in asthma and chronic obstructive pulmonary disease (COPD). However, it has the potential to induce bronchospasm and fall in arterial oxygen saturation (SaO₂) in some patients and the safety of the method in interstitial lung disease (ILD) has not been determined. The aim of this study was to examine the effect of SI procedure on spirometric results and SaO₂ in patients with ILD. Materials and methods: We studied prospectively 59 patients (33 males, 26 females) with different ILD (36—sarcoidosis, 16—hypersensitivity pneumonitis, 7—idiopathic pulmonary fibrosis). Sputum was induced by 4 sequential 5 min inhalations of 5% saline solution and FEV₁, FVC and SaO₂ were measured at 5, 10, 15 and 20 minutes of induction. Results: The procedure was well tolerated, and none of the patients experienced excessive bronchoconstriction, defined as a fall in FEV₁ of ≥20%. Nine patients (15%) had a fall in FEV₁ of ≥10% from the baseline; a drop in FVC of ≥10% from the baseline was observed in 10 subjects. The mean (SD) maximum per cent fall in FEV₁ was 6.3 ± 4.4%, and in FVC—6.4 ± 4.6%. The maximum per cent fall in FEV₁ did not correlate with baseline FEV₁% predicted (r = −0.099). SaO₂ was measured in 42 patients. There was a very small fall in SaO₂ at 5, 10, 15 and 20 min of induction, although statistically significant (baseline SaO₂ = 96.7 ± 1.9% vs. 95.8 ± 2.4%, p = 0.002; vs. 96.1 ± 2.2%, p = 0.0114; vs. 95.7 ± 2.4%, p = 0.0016; vs. 95.9 ± 2.0%; p = 0.0038, respectively). No significant relationship was found between fall in FEV₁, FVC or SaO₂ after induction and diagnosis or smoking history. Conclusions: Sputum induction is safe and well tolerated in patients with ILD.