Background: A crucial issue in the analysis of exhaled breath is the collection of gaseous samples. The analysis of pure alveolar gas is the method of choice if contamination of samples is to be minimized. Monitoring of expired CO2 can be used to identify alveolar gas. The purpose of this study was to evaluate a bed side version of this technique using visual CO2 control by means of a capnometer.
Methods: 22 mechanically ventilated patients of an ICU were enrolled into the study. Alveolar and mixed expiratory gas, and arterial blood were sampled. PCO2 in blood and gas was determined in a blood gas analyzer. End tidal PCO2 was monitored in all patients by a fast responding main stream capnometry. Taking the gaseous samples was visually synchronized with the expired CO2.
Results: Alveolar CO2 contents measured during two different respiratory cycles were identical (p 0.86). The variation of the CO2 content during 10 measurements in one patient was lower than 4%. Arterial PCO2, PCO2 in alveolar gas and end tidal PCO2 showed positive correlation.
Conclusions: The visually CO2-controlled sampling technique of alveolar gas is a reliable and reproducible method. It represents an important step in simplifying and standardizing breath analysis.