Exhaled Breath Condensate Isoprostanes Are Elevated in Patients With Acute Lung Injury or ARDS

Oxidant stress is a purported mechanism of tissue damage in patients with ARDS and acute lung injury (ALI). Isoprostanes, prostanoid compounds primarily formed nonenzymatically via lipid peroxidation, are precise markers of in vivo oxidant stress. Plasma levels of metabolites of 8-iso-prostaglandin-F2α (8-iso-PGF2α) correlate with outcome in patients with ARDS. To examine exhaled breath condensate levels of 8-iso-PGF2α as a noninvasive quantification of pulmonary oxidant stress in patients with, or at risk for, ARDS/ALI. Breath condensate was collected from 22 patients with, or at risk for, ARDS/ALI by placing Tygon tubing submerged in an ice bath in line with the expiratory limb of the ventilator circuit. Ten patients without lung disease, who were intubated while undergoing minor surgical procedures, served as control subjects. Between 1 and 3 mL of condensate was collected over a 30- to 60-min period, then immediately frozen and stored at −70°C until analysis. The 8-iso-PGF2α was purified and derivatized, then quantified by stable isotope dilution in conjunction with gas chromatography/mass spectrometry. The mean level of exhaled 8-iso-PGF2α in the patients with ALI/ARDS, 87 ± 28 pg/mL, was significantly higher than the mean in the normal group, 7 ± 4 pg/mL (p = 0.007). The 8-iso-PGF2α levels were greater than two standard deviations above the mean of the normal group in 12 of 22 patients with or at risk for ARDS/ALI. These results provide further evidence that lipid peroxidation does occur in patients with ARDS/ALI. The measurement of exhaled isoprostanes provides a novel, noninvasive method to quantify oxidant stress in such patients.