[Usefulness of NODSS (nasal/oral discriminate sampling system) in end-tidal carbon dioxide gas monitoring].

We investigated the usefulness of nasal/oral discriminate sampling system (NODSS) that had been developed recently in order to obtain the accurate end-tidal carbon dioxide (PET(CO2)) from a spontaneously breathing patient through a nomal airway. Fifty patients were monitored using a capnograph with NODSS following extubation in the postanesthesia unit. PET(CO2) data were collected by means of nasal, oral or nasal/oral sampling. The levels of arterial carbon dioxide (PaCO2) were determined simultaneously. In addition to examining the correlation between PET(CO2) and PaCO2, we investigated the influence of method of anesthesia, age and respiratory rate on the (PaCO2 - PET(CO2)) gradient. In most patients without nasal obstruction breathing through the nostril, PET(CO2) determined by selective nasal sampling was closer to PaCO2 than those by oral or nasal/oral sampling. Furthermore, the mean (PaCO2 - PET(CO2)) gradient was 4.98 mmHg in patients aged over 60, while it was 2.02 mmHg in patients aged under 60, suggesting that PET(CO2) could not be a good index in elderly people. There was no significant difference in the mean (PaCO2 - PET(CO2)) gradient among different methods of anesthesia. In conclusion, NODSS was useful in determining PET(CO2) more accurately and estimating PaCO2 precisely when used in relatively young people by selective nasal or oral sampling.