P146 Can exhaled hydrogen sulphide and hydrogen cyanide be used to diagnose pneumonia in the Intensive Care Unit?

Introduction Hydrogen sulphide (H2S) and hydrogen cyanide (HCN) have been proposed as biomarkers of infection and inflammation, and therefore may be useful in the Intensive Care Unit (ICU) to diagnose or monitor pulmonary infection. Our aims were to monitor breath H2S and HCN concentrations in intubated, ventilated patients with pulmonary infiltrates on CXR and correlate them with clinical features and serum H2S and HCN concentrations. Methods Adult patients ventilated on controlled modes with new pulmonary infiltrates on CXR were recruited from Christchurch Hospital ICU. Once daily end-tidal breath samples were collected and analysed off-line by selected ion flow tube mass spectrometry (SIFT-MS). Initial breath samples and concurrent arterial blood samples were obtained after intubation. Results Twenty-eight patients were recruited (17 male), median age 61.5 years (range 26–85 years). Median breath H2S concentration of all samples was 0.96 ppb (range 0.22–5.12 ppb, median intra-subject CV 9.97%) and HCN concentration 0.76 ppb (range 0.31–11.5 ppb, median intra-subject CV 8.53%) collected over a median of 3 days (range 1–8 days). In general, there was little variation in breath volatile concentration over time. There was a weak relationship between breath and blood HCN concentrations (rs = 0.39, p = 0.04). Breath concentrations were not significantly higher than inspired concentrations. Inspired and exhaled volatile concentrations were related (H2S rs = 0.83, p < 0.0001; HCN rs = 0.66, p < 0.0001). Breath H2S and HCN concentrations could not be used to differentiate between patients with pneumonia and those with pulmonary infiltrates due to conditions other than pneumonia. Exhaled volatile concentrations could not separate patients with SIRS or sepsis from those without SIRS or sepsis. Conclusions As far as we are aware, this is the first study to explore breath H2S and HCN concentrations in ventilated ICU patients. There was no difference in breath volatile concentrations between patients with pulmonary infiltrates caused by different conditions. Using this breath collection method, there is no role for the use of breath H2S or HCN in the diagnosis or monitoring of pneumonia in critical illness. Abstract P146 Table 1. Causes of pulmonary infiltrates as determined by clinical factors, radiological and microbiological results, and initial breath volatile concentrations for each condition. Cause of pulmonary infiltrates Number of patients (%) Median H2S conc