Limitations of the Technique to Determine Hydrogen Peroxide Levels in Exhaled Breath Condensate From Patients With Adult Respiratory Distress Syndrome

OBJECTIVE: Exhaled breath condensate represents an alternative to bronchoalveolar lavage for the analysis of markers of inflammation and oxidative stress in patients with adult respiratory distress syndrome (ARDS). However, analysis of hydrogen peroxide (H 2 O 2 ) yields variable results that do not correlate with severity of the clinical presentation. In an attempt to explain this variability, the aim of the present study was to assess the possible limitations of the most commonly used technique for analyzing H 2 O 2 in breath condensate. PATIENTS AND METHODS :H 2 O 2 levels were analyzed using the Gallati technique (linear range between 0.3 and 10 µM, r=0.99; P<.05) in serial samples of condensate taken from the expiratory tube of a mechanical ventilator in 6 patients with ARDS. RESULTS: The volume of condensate obtained correlated to minute ventilation (r=0.96; P<.05). In 11 out of 23 samples, a spectrophotometer reading was obtained at 450 nm despite the absence of the characteristic color of the reaction and in some of these samples a spontaneous reading was obtained that was indicative of contamination. The absorbance spectrum of these samples did not contain the characteristic peak for H 2 O 2 at 450 nm and pretreatment of some samples with catalase did not affect the absorbance at 450 nm. CONCLUSIONS: The spectrophotometric method commonly used to measure H 2 O 2 levels in breath condensate lacks specificity in ARDS due to the presence of variable levels of contaminants in the samples, which lead to false positives.