Abstract: An arrangement for introducing a liquid into the body of a patient or for withdrawing a liquid from the body of a patient, including a first structural part carrying a cannula for positioning in the body of the patient, and a second structural part with a connection port for detachably coupling a conduit for supplying or withdrawing a liquid, wherein the first and second structural parts are connected, can be rotated relative to each another and in relative rotational positions form a channel for introducing a liquid from the conduit to the cannula or for withdrawing a liquid from the cannula to the conduit, and whereby movement of the conduit for coupling and uncoupling is transverse to the longitudinal axis of the cannula.