Early Detection of Ventilator-Associated Pneumonia from Exhaled Breath in ICU Patients

Abstract

Objectives: Evaluate associations between volatile organic compounds (VOCs) in heat and moisture exchange (HME) filters and the presence of ventilator-associated pneumonia (VAP). Summary Background Data: Clinical diagnostic criteria for VAP have poor inter-observer reliability, and cultures are slow to result. Exhaled breath contains VOCs related to Gram-negative bacterial proliferation, the most identified organisms in VAP. We hypothesized that exhaled VOCs on HME filters can predict nascent VAP in mechanically ventilated ICU patients. Methods: Gas chromatography-mass spectrometry (GC-MS) was used to analyze 111 heat and moisture exchange (HME) filters from 12 intubated patients who developed VAP. Identities and relative amounts of VOCs were associated with dates of clinical suspicion and culture confirmation of VAP. Matched pairs t-tests were performed to compare VOC abundances in HME filters collected within three days pre- and post-clinical suspicion of VAP (pneumonia days), versus outside of these days (non-pneumonia days). A ROC curve was generated to determine the diagnostic potential of VOCs. Results: Carbon disulfide, associated with the proliferation of certain Gram-negative bacteria, was found in samples collected during pneumonia days for 11 of 12 patients. Carbon disulfide levels were significantly greater (P=0.0163) for filters on pneumonia days. The AUROC for carbon disulfide was 0.649 (95%CI 0.419-0.88). Conclusions: Carbon disulfide associated with Gram-negative VAP can be identified on HME filters up to three days prior to the initial clinical suspicion, and approximately a week prior to culture confirmation. This suggests VOC sensors may have potential as an adjunctive method for early detection of VAP.