| Popis: |
The analysis of volatile organic compounds (VOCs) in breath may be a useful non-invasive tool in the Intensive Care Unit (ICU) to monitor metabolic and oxidative stress or diagnose pulmonary infection. Acetone is produced during starvation and metabolic stress, hydrogen sulphide (H2S) may be a marker of inflammation and infection and hydrogen cyanide (HCN) may also act as a marker of infection, particularly caused by Pseudomonas aeruginosa. Firstly, the effects on measured VOC concentrations of the breath collection equipment and storage were assessed. Sample humidity declined faster than any analyte. Sample losses of 21%, 25% and 24% for acetone, H2S and HCN, respectively, were seen as a result of being passed through the sampling apparatus. Over 90% of initial breath VOC concentrations were detectable after 90 min storage in Tedlar bags at 40°C. Secondly, a breath collection method for off-line analysis was validated in 20 mechanically ventilated patients in the ICU. The effect on VOC concentrations of breath sampling from two locations after two breathing manoeuvres was explored, revealing significantly higher analyte concentrations in samples from the airways than from a T-piece in the breathing circuit, and after tidal breathing compared to a recruitment-style breath. Practical difficulties were encountered using direct airway sampling and delivering recruitment style breaths; end-tidal breath sampling from the T-piece was simplest to perform and results equally reproducible. Breath samples from 26 healthy anaesthetised controls were used to validate a breath collection method in the operating theatre. The effects of altering anaesthesia machine settings on inspiratory and exhaled acetone concentrations were explored. A difference in median inspiratory, but not exhaled, acetone concentrations was observed between the anaesthesia machines (ADU Carestation 276 ppb, Aysis Carestation 131 ppb, p=0.0005). Closing the adjustable pressure limiting (APL) valve resulted in a reduction in exhaled acetone concentration, as did breath sampling distal to the circuit filter, due to dilution by dead space air. Median (range) breath concentrations for samples collected on the patient side of the circuit filter with the APL valve open (n=22): acetone 738 ppb (257–6594 ppb), H2S 1.00 ppb (0.71-2.49 ppb), HCN 0.82 ppb (0.60-1.51 ppb). Breath acetone concentration was related to plasma acetone (rs=0.80, p |
