Mechanical ventilation injures lungs, but there are currently no reliable methods for detecting early injury. We therefore evaluated whether exhaled pentanal, a lipid peroxidation product, might be a useful breath biomarker for stretch-induced lung injury in rats.
A total of 150 male Sprague-Dawley rats were investigated in 2 substudies. The first randomly assigned 75 rats to 7 hours of mechanical ventilation at tidal volumes of 6, 8, 12, 16, and 20 mL·kg−1. The second included 75 rats. A reference group was ventilated at a tidal volume of 6 mL·kg−1 for 10 hours 4 interventional groups were ventilated at a tidal volume of 6 mL·kg−1 for 1 hour, and then for 0.5, 1, 2, or 3 hours at a tidal volume of 16 mL.kg−1 before returning to a tidal volume of 6 mL·kg−1 for additional 6 hours. Exhaled pentanal was monitored by multicapillary column–ion mobility spectrometry. The first substudy included cytokine and leukocyte measurements in blood and bronchoalveolar fluid, histological assessment of the proportion of alveolar space, and measurements of myeloperoxidase activity in lung tissue. The second substudy included measurements of pentanal in arterial blood plasma, cytokine and leukocyte concentrations in bronchoalveolar fluid, and cleaved caspase 3 in lung tissue.
Exhaled pentanal concentrations increased by only 0.5 ppb·h−1 (95% confidence interval [CI], 0.3–0.6) when rats were ventilated at 6 mL·kg−1. In contrast, exhaled pentanal concentrations increased substantially and roughly linearly at higher tidal volumes, up to 3.1 ppb·h−1 (95% CI, 2.3–3.8) at tidal volumes of 20 mL·kg−1. Exhaled pentanal increased at average rates between 1.0 ppb·h−1 (95% CI, 0.3–1.7) and 2.5 ppb·h−1 (95% CI, 1.4–3.6) after the onset of 16 mL·kg−1 tidal volumes and decreased rapidly by a median of 2 ppb (interquartile range [IQR], 0.9–3.2), corresponding to a 38% (IQR, 31–43) reduction when tidal volume returned to 6 mL·kg−1. Tidal volume, inspiratory pressure, and mechanical power were positively associated with pentanal exhalation. Exhaled and plasma pentanal were uncorrelated. Alveolar space decreased and inflammatory markers in bronchoalveolar lavage fluid increased in animals ventilated at high tidal volumes. Short, intermittent ventilation at high tidal volumes for up to 3 hours increased neither inflammatory markers in bronchoalveolar fluid nor the proportion of cleaved caspase 3 in lung tissue.
Exhaled pentanal is a potential biomarker for early detection of ventilator-induced lung injury in rats.