The study objective consists in sequential collection of exhaled breath condensates (EBC) in ICU patients receiving invasive ventilation. The EBC samples will be subjected to determination of volatile organic compound (VOC) profiles by Stimulated Raman Spectroscopy (SRS) which, upon individual matching to routinely collected clinical parameters, may become putative biomarkers for the early recognition of VAP. Evidence has accumulated in support of the assumption that certain metabolites in EBC might display significant profile differences as to their size, hydrophobicity and electrical charge. Identification of VAP-specific profiles of VOC will provide the basis for the generation of a data base enabling the construction and standardization of a bedside device for continuous real-time point-of-care monitoring of VAP hazard in patients on invasive ventilation.