Apparatus and methods are described including a trocar (40) that defines a lumen therethrough, configured to provide a passage through skin of a subject into a body of the subject. A cannula (60) is configured to be placed into the subjects body via the passage provided by the trocar, the cannula being configured to be slidable with respect to the trocar. The cannula includes an outer tube (64) having a first expandable element (77) disposed at a distal end thereof, and an inner tube (62) having a second expandable element (72) disposed at a distal end thereof, the inner tube being configured to be slidable with respect to the outer tube. A vacuum port (61) applies vacuum pressure to the first expandable element via a space (65) between the inner and outer tubes of the cannula. Other applications are also described.
