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Short, hollow cylinders or tubes for insertion into a canal, vessel, passageway, body cavity, or duct. Cannulae usually consist of a small-length rigid or semirigid plastic or metal tube, a handle, and a valve. The valve regulates the pressure within the cavity. Most cannulae are fitted with a trocar or stylet during insertion. After insertion, the trocar is withdrawn, providing a rigid or semirigid structure that can be connected to an external tube, catheter, or connector for the injection or withdrawal of substances. Cannulae may also provide a port through which diagnostic or surgical instruments are passed to gain access to and operate on internal structures. They can be used in a great variety of therapeutic and diagnostic procedures.
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