Figure 1: Changes in TC-CO2 and ETCO2 with 3 L/min of O2 supplied with a nasal or mouth-nose cannula during intravenous sedation. The capnometer in the nasal cannula showed a lower peak ETCO2 concentration immediately after midazolam injection than before injection. The capnometer in the mouth-nose cannula sometimes showed a lower peak ETCO2 concentration immediately after midazolam injection.