cannula

A cannula is a slender tube that can be inserted into a body cavity, vessel, or duct to facilitate administration or withdrawal of fluids, gases, or to provide a channel for instrumentation. It is typically a flexible catheter that remains in place while the trocar or introducer is removed, or it can be a sterile tubular instrument used to gain access.

Common forms include intravenous cannulas, which are inserted into a vein to deliver fluids or medications and for blood sampling; they vary in size and are usually cataloged by gauge or French size. Peripheral venous cannulas are short and placed in peripheral veins; central venous cannulas are longer and placed in central veins for extended therapy and monitoring. A nasal cannula delivers supplemental oxygen through the nostrils; an arterial cannula allows arterial access for continuous blood pressure monitoring or repeated sampling. A chest or pleural cannula, or chest tube, provides drainage of air or fluid from the pleural space.

Materials include medical-grade silicone or polyurethane; some older devices use latex. Sizes range from small gauges for peripheral venous cannulas to larger diameters for chest and central lines. In many cases, a guidewire and introducer are used (Seldinger technique) to place the cannula safely. Sterile technique is essential. Care includes regular assessment of patency, securement, and monitoring for signs of infection or infiltration. Removal should be performed when no longer needed, with site flushed to restore patency if appropriate.