PCA is a method by which patients control the amount of analgesia they receive. There are a number of different PCA systems. In the classic PCA system, the patient receives a preset does of morphine by pressing a button on a computerized pump that is connected to an IV catheter. With PCA, the patient may receive a small continuous flow of morphine and add more morphine as needed to provide a more constant level of comfort. Studies have shown that patients using PCA often use less morphine than do patients who are not PCA. In a very different type of PCA system, the pain reliever fentanyl (Duragesic) is delivered through the skin, eliminating the need for an IV and for programming a pump.