This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anesthesia Machine, Subject name: Anaesthesia
[{'content': 'Which of the following mechanism prevents fitting of wrong gas cylinder to the anaesthesia machine in operation theatre? (Repeat) \nSelect and explain. \nA. Pin index system, B. Yolk assembly, C. Bodock seal, D. Gas analyser', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: A (Pin index system) Ref: Miller Textbook of Anaesthesia. 6th edition Explanation:The Pin Index Safety System, or PISS, is a safety system that uses geometric features on the yoke to ensure that pneumatic connections between a gas cylinder and a machine that uses pressurized gases are not connected to the wrong gas yoke.This system can be seen on an anesthesia machine.Each gas cylinder has a pin configuration to fit its respective gas yoke.PIN Index of Commonly Used Gases in AnesthesiaO2: 2-5N2O: 3-5Air: 1-5CO2: 1-6Heliox: 2-4 Entonox: 7', 'role': 'assistant'}]