End tidal carbon dioxide tension (ETCO₂), the partial pressure of exhaled CO₂ obtained at the end of tidal breath measured by capnometer, can enable PaCO₂ estimation and the monitoring of adequate ventilation. However, there are many factors that may affect ETCO₂. Recently, we experienced a patient that developed an abrupt increase of ETCO₂ of over 10 mmHg following the subcutaneous infiltration of a high dose of epinephrine for intraoperative hemostasis. This increase in ETCO₂ may have been caused by an increased cardiac output and an increase in CO₂ production due to increased tissue metabolism. Therefore, when we use ETCO₂ to monitor a patient's ventilation, we should bear in mind that three factors - ventilation, hemodynamics and metabolism, may affect the the determined ETCO₂ level.