Screening For Respiratory Infection By Breath Volatiles In Mechanically Ventilated Patients

Rationale: Exhaled breath volatile organic compounds (VOCs), arising from or altered by disease, have potential uses as biomarkers for diagnostics or monitoring in critically ill patients. We have developed a methodology for VOC capture, and tested it in ventilated patients on the intensive care unit. In parallel we have profiled VOCs in the headspace of relevant pathogens. Methods: In vitro: Human pathogen isolates were grown in culture media as well as human tracheal aspirates, and headspace VOCs profiled by gas chromatography mass spectrometry (GC-MS). In vivo: Adsorbent traps were exposed to 1 L samples of breath from each subject, with up to three serial samples per patient collected at baseline (within 48hrs of intubation), then at 2-3 day intervals up to a maximum of 10 days. Samples were analyzed within 72 hrs by GC-MS. Data analysis: A fingerprint recognition algorithm was developed to analyze GC-MS data, based on spectral angle classification which allows for the direct comparison of mass spectra extracted from peaks in a total ion chromatogram. Results: Samples were collected from 46 ventilated patients with severe sterile tissue injury at baseline, the majority with traumatic brain injury and few with significant pre-existing comorbidities. Serial samples were obtained in 26 of these. Pathogens were isolated from the lower respiratory tract (>104 cfu/ml) in almost half the subjects. The VOC sampling procedure took one minute per sample and was well tolerated in every patient. An average of 195 spectral peaks were identified per patient. Initial analysis showed intra subject/same-day reproducibility to be good. Thus far, we have found common VOC profiles in the headspace of Aspergillus fumigatus and Pseudomonas aeruginosa cultures and in the breath samples of patients where the organisms have been cultured from respiratory tract samples. Conclusion: Our methodology for VOC sampling in critically ill ventilated patients was well tolerated and gave reproducible results. We have confirmed that VOCs detected in the headspace of cultured pathogens are also detectable in breath samples of patients isolating the organism by this method. This may therefore provide an appropriate platform for novel biomarker discovery on the intensive care unit, in particular related to the detection and/or exclusion of healthcare associated infection.