<prompt> The site for central venous cannulation with least incidence of infection:-Subclan veinFemoral veinInternal jugular veinExternal jugular vein  <response>: subclan vein is the site with least infection and best patient tolerance. BUT ;the demerit is tourous course and high risk for pneumothorax Right internal jugular vein is the most preferred for central venous cannulation Reasons for this preference are: Absence of valves. Consistent anatomic location of the internal jugular vein. Easily identifiable surface landmarks. Direct communication with the right atrium. Other sites: Subclan vein - greater risk of pneumothorax. Left internal jugular vein - greater risk of pleural effusion chylothorax. Femoral vein - increased risk of thromboembolic complications, infection and vascular injury. 