Abstract: A method and an apparatus are disclosed for removal of an existing cannula from a patient and insertion of a replacement cannula into the patient, through the same passageway, by use of a guide rod which maintains the passageway intact. The guide rod is first installed through the existing cannula, and the existing cannula is removed. A hollow trocar, carrying a replacement cannula, is inserted into the patient over the guide rod, then the guide rod and the trocar are removed, leaving the replacement cannula in place in the patient. The guide rod can be fitted with an expandable anchor to hold the guide rod in place during removal of the existing cannula and insertion of the trocar.