A device for forming and/or maintaining a percutaneous access pathway into a body of a patient, comprising: an access pathway catheter configured to connect an internal portion of a body of a patient to an external environment; an access pathway port configured to maintain a barrier between the internal portion of the body and the external environment, the access pathway port including an access pathway port door for selectively opening and closing an access pathway formed by the access pathway catheter and the access pathway port, and a distal opening through which the access pathway catheter is configured to extend into the internal portion of the body; and an attachment device connectable to the access pathway port and configured to selectively cause the access pathway port door to open; the attachment device including: an insertable part, and an internally sterile attachment device sheath at least partially surrounding said insertable part and configured to enable insertion of said insertable part of the attachment device into the internal portion of the body through the access pathway port door in the access pathway, while the attachment device is connected to the access pathway port; characterised in that the attachment device further includes an attachment device port, the attachment device being connectable to the access pathway port by connection of the attachment device port to the access pathway port; and the access pathway port and the attachment device port include respective locking keys (47, 156) and are connectable together via the locking keys (47, 156); and the access pathway port and the attachment device port include respective mechanisms operable, by rotation in relation to each other, to force the access pathway port door to open; and said respective mechanisms are configured to prevent removal of the access pathway port from the attachment device port until the access pathway port door can close fully. an access pathway catheter configured to connect an internal portion of a body of a patient to an external environment; an access pathway port configured to maintain a barrier between the internal portion of the body and the external environment, the access pathway port including an access pathway port door for selectively opening and closing an access pathway formed by the access pathway catheter and the access pathway port, and a distal opening through which the access pathway catheter is configured to extend into the internal portion of the body; and an access pathway port door for selectively opening and closing an access pathway formed by the access pathway catheter and the access pathway port, and a distal opening through which the access pathway catheter is configured to extend into the internal portion of the body; and an attachment device connectable to the access pathway port and configured to selectively cause the access pathway port door to open; the attachment device including: an insertable part, and an internally sterile attachment device sheath at least partially surrounding said insertable part and configured to enable insertion of said insertable part of the attachment device into the internal portion of the body through the access pathway port door in the access pathway, while the attachment device is connected to the access pathway port; characterised in that an insertable part, and an internally sterile attachment device sheath at least partially surrounding said insertable part and configured to enable insertion of said insertable part of the attachment device into the internal portion of the body through the access pathway port door in the access pathway, while the attachment device is connected to the access pathway port; the attachment device further includes an attachment device port, the attachment device being connectable to the access pathway port by connection of the attachment device port to the access pathway port; and the access pathway port and the attachment device port include respective locking keys (47, 156) and are connectable together via the locking keys (47, 156); and the access pathway port and the attachment device port include respective mechanisms operable, by rotation in relation to each other, to force the access pathway port door to open; and said respective mechanisms are configured to prevent removal of the access pathway port from the attachment device port until the access pathway port door can close fully.