The invention relates to a chest drainage system (100) for creating and maintaining a sub-atmospheric pressure within the pleural cavity and/or the mediastinum of a patient (P). The system has a chest drainage unit (CDU, 10) with an internal cavity (C) having a first chamber part (C1, 11) and a second chamber part (C2, 12) with an air outlet from the CDU, and a liquid seal chamber (LSC, 13). The second chamber part (C2, 12) of the chest drainage unit is connected to a carbon dioxide sensor (CO2S, 15) for detecting carbon dioxide in any air passing through the liquid seal chamber (LSC, 13), the carbon dioxide sensor being capable of detecting carbon dioxide by a visible color change from a chemical reaction occurring in the carbon dioxide sensor between carbon dioxide and a detector reactant (DC) positioned in the carbon dioxide sensor. Preliminary test performed by the inventor have demonstrated that the present invention is very effective in determine whether, or not, carbon dioxide is present in the air passing through the chest drainage unit, this information being highly important in the subsequent decision of continuing the treatment with the chest drainage system.
