A cannula having a hollow metal tube for injection of liquids such as an anesthetic, or RF energy, into a patient. A thermocouple or other temperature sensor is located at the bare tip of the cannula, and a wire for the temperature sensor extends along the length of the cannula, preferably in a groove formed in the tube, or through a passageway formed in the tube. An outer insulation layer covers the tube and wire. Thus, a single device serves as both a cannula and an electrode.