It is very important to choose the best central venous catheterization route for trauma patients, the determinants that need to be considered comprehensively include coagulation dysfunction, fracture of the clavicle on the side of the puncture, and tracheotomy care. More importantly, whether it can used simultaneously for accurate volume and invasive hemodynamic monitoring. For the purpose of support of cardiopulmonary function, the ideal position of the catheter tip is vital with regard to an accurate CVP and hemodynamic monitoring. Cannulation of the axillary vein is ideal for patients with severe poly-trauma because it avoids the thoracic cavity, intercostal arteries, tracheostomy, and clavicle, and is prone to compression even if the artery is injured. At present, there is no systematic introduction of ultrasound-guided axillary vein catheterization in the trauma ICU in the literature. Since Oct 2021, the investigators have attempted to practice axillary vein catheterization for this crucial trauma population; unfortunately, the investigators have not know till now whether this procedure is associated with accurate tip placement and its safety should also be weighted. So it is necessary to summarize the relevant clinical data.

Inclusion Criteria:

• Trauma patients admitted to TICU
• Receiving axillary vein catheterization during TICU stay

Exclusion Criteria:

• Without record of axillary vein catheterization
• Without imaging confirming （X-ray or chest CT） the location of catheter tip

Our study do not consider limits on age, sex, or pregnant.