An infusion set is used with an insulin pump as part of intensive insulin therapy. The purpose of an infusion set is to deliver insulin under the skin. It is a complete tubing system to connect an insulin pump to the pump user: it includes a subcutaneous cannula, adhesive mount, quick-disconnect, and a pump cartridge connector.
Firstly, the user must attach a reservoir of insulin to the set and connect it to the pump. The set is then "primed" - the pump pushes insulin quickly through the tubing and the cannula to ensure no air is in the system before insertion. Note that it is vital that the infusion set is not inserted into the skin when the set is being primed (as this could result in the accidental delivery of a large dose of insulin). The user then peels off the paper protecting the adhesive pad and carefully inserts the needle beneath the skin.
The cannula is usually made of flexible plastic, which allows it to move without causing discomfort to the patient. The needle is pushed into the layer of fat below the skin, taking the plastic cannula with it. The needle is then removed, leaving the cannula in place. Insertion should be done in a fairly swift movement to avoid the cannula "bunching up" around the needle. The needle is then removed, leaving the cannula below the skin.
A few pump users prefer an infusion set with a steel needle instead of a cannula. The cannula surrounds a steel needle similar to that found on a hypodermic syringe.