Final answer:
Ethylene oxide is the agent used for sterilizing the plastic tubing of heart-lung machines, suitable for cold sterilization of heat-sensitive equipment.
Step-by-step explanation:
The agent used to sterilize the plastic tubing of heart-lung machines is ethylene oxide. Ethylene oxide is a gas sterilant and an alkylating agent recognized for its ability to penetrate and sterilize items that are in plastic packaging, such as medical equipment and devices used in heart-lung machines.
Due to its characteristics, ethylene oxide is ideal for cold sterilization, which is essential for heat-sensitive equipment. Despite its effectiveness, it requires careful handling because it is both highly explosive and carcinogenic.