A cannula, in the broad sense of the word, is a tube that is inserted into the body with the purpose to either deliver some type of fluid or remove it.
Here’s how it works: Flexible tubing is connected at one end to the insulin pump and at the other end to the cannula, which is a hollow needle. The cannula is inserted into the subcutaneous tissue (tissue just under the skin) usually in the abdominal region. The insulin that flows from the pump through tubing and into the body through the cannula replaces injections using syringes. The cannula is held in place by adhesive material so that it will not dislodge during activity.
The cannula typically remains in the same inserted location for about three days before it is replaced and reinserted into a new location to prevent infection.