Patients admitted to the Intensive Care Unit (ICU) often have acute respiratory failure. Tracheal intubation, which is a routine procedure in the ICU, is related with a high frequency of complications because of the dangerous respiratory status of critically ill patients. Therefore, it is necessary to evaluate the state of the airways in patients intubated and mechanically ventilated, as well as endotracheal tube position. A 3D airway model has been used in order to model the air-flow. However, chest Computed Tomography (CT) image is needed in order to obtain a 3D model. This paper presents a non-rigid registration between a TC image obtained in ICU under critical conditions, and a CT image acquired under controlled conditions.