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.
Using an infusion set
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.
The same used device can't be reused for the other patient, even if the set is washed or re-sterile. As it is not a surgical instrument. It is for single use only.
Some pump users prefer to use an insertion device to insert their sets, rather than pushing the needle in by hand. These are spring-loaded and are designed to push the needle into the skin quickly and (usually) painlessly. The user simply loads the primed set into the insertion device, peels off the paper protecting the adhesive pad, places the device against the skin and presses a button. This may be an advantage for those with needle phobia.
Sites for infusion sets
Many pump users site their infusion sets on the abdomen, in a roughly semicircular area around and below the navel. Other sites include the upper leg, upper buttocks, hips, upper arms and lower back. Insulin absorption may vary from site to site, so it is important that patients are advised of the most effective sites to use by their diabetes adviser.
Rotation of sites
The infusion set must be replaced regularly, usually every 2–3 days. Insulin absorption becomes less effective the longer the set is left in place, leading to poorer control of blood glucose. For this reason, the site of the infusion set is moved when the set is changed. Often a number of favorite sites for the infusion set are used on a rotation basis.
Disconnecting the set
The set can be disconnected from the pump and tubing with a quick-release that leaves the cannula and adhesive pad in place. This is convenient when swimming or showering (since most pumps are not fully waterproof), or when engaging in any activity when it is not desirable to be attached to the pump.
Types of infusion set
There are several types, styles, and sizes of infusion sets available to allow an insulin pump user a choice to customize what works best for them. These vary in cannula length, cannula entry angle and in the length of tube connecting the cannula to the pump. For instance, an individual with little body fat may choose to use a set with a short cannula that enters the skin at a shallow angle, whereas an individual with more body fat may find that a longer cannula entering at right angles to the skin works best. Most infusion sets have a standard Luer Lock connector so that they will mate to most insulin pumps. However, this is not always the case: some pump manufactures use a pump specific connector to provide additional features such as venting or a more secure connection between the pump and the infusion set. Use of these non-standard connections may limit the infusion set sources available to customers.