This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Monitoring in Anesthesia, Subject name: Anaesthesia
[{'content': 'The site for central venous cannulation with least incidence of infection:- \nSelect and explain. \nA. Subclan vein, B. Femoral vein, C. Internal jugular vein, D. External jugular vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.', 'role': 'assistant'}]