A pain relief system known as patient-controlled analgesia (PCA) allows patients to give themselves small but frequent doses of pain medicine without having to call a nurse. It is used most often in the hospital after surgery. The concept is simple: A pump containing pain medicine is attached to an intravenous (IV) line (which goes into a vein). When the patient feels pain, he or she pushes the button on the pump and they receive a dose of medicine. But the button on this pain relief system must be pushed only by the patient, not by others.