[Measurement of end-expiratory carbon dioxide values in pediatric anesthesia]

This study dealt with two principles of the evaluation of end-expiratory CO2 in pediatric anaesthesia: detection of CO2-influenced infrared rays with a full stream analyzer attached to the tracheal tube; CO2 measurement with a side-stream analyzer connected to the breathing and ventilating system by a small tube. The linearity of the analyzers was tested with gas mixtures containing 3.0/5.0/7.0 vol% of CO2 cycling at an increasing rate. Additional mass-spectrometry has proven that the instruments are accurate within the clinical range of pediatric anesthesia. A maximal deviation of 8% develops when cycling rates increase to 40 per min. To detect quality differences in the analyzers, tangential constructions onto the CO2 curves plotted by the capnographs provided valuable quotients. Depending on the length of the tubing that feeds samples of respiratory gas into the side-stream analyzer, the CO2 curves were subject to sinus degradation with increasing respiratory rates. Capnography with full-stream analyzers depended on inspiratory zero CO2 content for reference purposes.