Extravasation detection electrode patch

An electrode patch for use in a non-invasive device for detecting extravasation that may occur when a needle with a tip is inserted into a patient in order to introduce fluid into the vascular system of a patient, comprising:

• a body of the patch adapted to be affixed to the skin of a patient,
• an outer pair of elongated electrodes and an inner pair of elongate electrodes, the length of each of said electrodes being deployed along the body of said patch,
• said inner pair of electrodes being spaced from one another on either side of a center line, said inner pair defining a measuring zone, said measuring zone being shaped and dimensioned to encompass a needle tip within said zone, said zone being small enough to optimize sensitivity, said inner pair being long enough to facilitate placement of the patch over a needle tip inserted into a patient,
• each of said outer pair of electrodes being outward, relative to said center line, of a respective one of said inner electrodes,
• energization of said outer electrodes, when said patch is affixed to the skin of a patient, providing a field which induces a signal in said inner electrodes that is a function of the impedance of the tissue in said measuring zone.