Superior vena cava aneurysm is a rare life-threatening intrathoracic vascular lesion. Contrast-enhanced CT examination plays an important role for surgical planning. It needs to choose the appropriate vein as the puncture site for contrast agent injection. Hereby we report a 22-year-old male presented with sudden-onset dyspnea and unconsciousness for 2 hours and suffered from cardiac arrest before visiting our hospital. The patient's condition is critically ill, and the risk of contrast agent extravasation and aneurysm explosion is high. We established a multi-disciplinary team, involving Emergency Department, Cardiac Surgery Department, Radiological Department and intravenous therapy experts, for the integrated assessment of patients. And we activate the emergency cooperation protocol for critically ill patients. The superior vena cava can't be used for contrast injection. Anatomically, the femoral vein drains blood back to the heart through the inferior vena cava, which could avoid the risk of rupture of the superior vena cava aneurysm due to excessive pressure of bolus injection of contrast agent. The indwelling of femoral vein puncture can be used in the treatment of critically ill patients. The vital signs of patients were closely observed during the examination process. No contrast agent extravasation and allergy reaction was observed and CT images were clear. The effective nursing cooperation in this case ensured the safety and effectiveness of the examination, and laid the foundation for further treatment.