Method and apparatuses for providing access to a body cavity of a living animal through an access port inserted in an incision made in a wall of the body cavity are disclosed. In some embodiments, the apparatus includes a cap configured to attach to the access port, the cap including an opening configured to permit insertion of a medical instrument through the cap and access port into the body cavity, and a tubular sleeve including a distal end sealingly connected at the opening and extending outwardly therefrom, the sleeve including a proximal end configured to receive and provide a seal with the medical instrument when received. The apparatus also includes a closure disposed to temporarily seal the sleeve prior to insertion of the medical instrument through the opening in the cap.