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RationaleThe concentration of octane and acetaldehyde in exhaled breath has good diagnostic accuracy for Acute Respiratory Distress Syndrome (ARDS). We aimed to determine whether breath octane and acetaldehyde are able to distinguish the presence and absence of ARDS in critically ill patients suspected to have ventilator-associated pneumonia (VAP).MethodsThis is a secondary analysis of a prospective observational study into exhaled breath analysis using gas-chromatography-time of flight-mass spectrometry. Difference in the relative abundance of octane and acetaldehyde in exhaled breath was compared between patients with and without ARDS using the Mann-Whitney U-test and the association was quantified using logistic regression. The discriminative accuracy of octane and acetaldehyde, alone or in combination, was calculated using the area under the curve of the ROC (AUROCC).ResultsWe included 98 patients of whom 32 had ARDS and 66 did not. The area under the acetaldehyde peak was higher in patients with ARDS (p=0.03), and associated with the presence of ARDS (OR: 1.06 per 100000 count change (95% CI: 1.02–1.13), p=0.01). A combined model with octane and acetaldehyde showed a high specificity and low sensitivity (respectively, 90% and 40.6%), with a low accuracy (AUROCC: 0.65, 95% CI: 0.53–0.78).ConclusionPatients suspected to have VAP with ARDS had a higher acetaldehyde concentration in exhaled breath than patients suspected to have VAP without ARDS. However, in this patient population, discrimination of these breath biomarkers for ARDS was poor, indicating the difficulty of translating diagnostic tests between clinical settings.