An extracorporeal blood gas exchange device has a bloodstream area for guiding a bloodstream, a gas-carrying area for guiding a gas flow, and a membrane, which forms a gas-liquid barrier between the bloodstream and the gas flow, and which further makes possible the transfer of carbon dioxide of the bloodstream into the gas flow. The device further has at least one measuring cuvette, which is separated from the bloodstream area at least partially by the membrane, so that carbon dioxide of the bloodstream can pass over into the measuring cuvette. The device has an optical measuring unit, which is configured to measure a carbon dioxide partial pressure present in the measuring cuvette.