A connector that links a patient to a device that collects or administers gases or liquids. It consists of a wide base onto which is mounted a cylinder with progressively smaller external threading (and looks a little like the tapering trunk of an evergreen tree). Christmas tree adapters are used to drain body fluids (for example by serving as connectors from indwelling urinary catheters to collection systems) or to administer medications (such as radiological contrast) or medical gases (such as oxygen).
When administering oxygen to a patient, all connectors used are green. Health care providers should confirm this color on the source of the gas and on all patient connections to avoid giving the wrong gas to the patient.