patient-controlled analgesia (PCA), a drug-delivery system that dispenses a preset intravascular dose of a narcotic analgesic when the patient pushes a switch on an electric cord. The device consists of a computerized pump with a chamber containing the drug. The patient administers a dose of narcotic when the need for pain relief arises. A lockout interval automatically inactivates the system if a patient tries to increase the amount of narcotic within a preset period.