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Early Detection of Ventilator-Associated Pneumonia from Exhaled Breath in ICU Patients
Carl I. Schulman1, *Umer Bakali2, *Chitvan Killawala2, *Michael Cobler-Lichter1, *Evelise Monteagudo2, *Luciana Tito Bustillos1, *Jessica Delamater1, *Larisa Shagabayeva1, *Brianna L. Collie1, *Nicole Lyons1, *Emre Dikici2, *Sapna Deo2, *Sylvia Daunert2
1Surgery, University of Miami Miller School of Medicine, Miami, FL; 2Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, FL

Objectives: Ventilator-associated pneumonia (VAP) represents a significant source of morbidity and mortality in critically ill patients. Clinical criteria used to diagnose VAP have poor inter-observer reliability, and culture results can often take days to become positive. Exhaled breath from patients contains volatile organic compounds (VOCs) related to the proliferation of Gram-negative bacteria, the most commonly identified organism s in VAP. We hypothesize that exhaled volatile organic compounds (VOCs) can be used to predict nascent VAP in mechanically ventilated ICU patients.
Methods: Heat and moisture exchange (HME) filters were collected several times per week from each of six intubated patients who developed VAP. These HME filters contain the VOCs from the exhaled gas as condensate that collects on the filter. HME filters were analyzed using a purge-and-trap gas chromatography-mass spectrometry (GC-MS) methodology to capture and identify VOCs present on each filter. A total of 36 filters were analyzed. The date of the first clinical suspicion of VAP was identified by chart review and subsequently confirmed by culture results. The identity and relative amounts of volatile compounds were recorded for each day and temporally associated with the onset of VAP. A one-tailed matched pairs t-test was performed matching samples collected within three days preceding the clinical diagnosis of VAP to those collected greater than three days prior to or post pneumonia.
Results: Over 100 unique compounds were identified from GC-MS analysis of HME filters collected from patients, which were broadly categorized into alcohols, ketones, aldehydes, hydrocarbons, sulfides, therapeutics, and anesthetics. Gram-negative species to which pneumoniae were attributed included Pseudomonas aeruginosa, Acinetobacter spp., Serratia spp., Stenotrophomonas spp., and E. coli. Sulfides associated with bacterial proliferation, including carbon disulfide, dimethyl disulfide, and carbonyl sulfide, were found in 83% of patients . The relative abundance of carbon disulfide was calculated to be 3 times greater for filters collected within three days preceding VAP diagnosis. Levels of carbon disulfide were significantly greater (p = 0.0296) for filters collected within three days preceding the clinical diagnosis of VAP, compared to those collected greater than three days prior to or post pneumonia (see Figure).
Conclusions: Sulfur-containing VOCs generated by bacteria can be identified from the exhaled breath of mechanically ventilated patients up to three days prior to the initial clinical suspicion of VAP, and over a week prior to culture confirmation of infection. This is a novel method using the evolution of VOCs to predict the onset of VAP in intubated ICU patients, and may inform the development of VOC sensors that can be integrated into ventilator circuits as an early warning method to better predict the onset of VAP.


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