A New Ground and Reference Technique for Invasive EEG Recordings

ABSTRACT. Objective: To demonstrate a subdermal wire electrode technique for establishing a ground (GND) and reference (REF) during long-term EEG monitoring (LTM) with intracranial electrodes. Usually, a separate GND and REF are required and this GND&REF pair can be selected contacts in the invasive electrode arrays themselves, special invasive electrodes, or Standard surface disc electrodes which require frequent maintenance. We investigated the use of a pair of chronic Subdermal Wire Electrodes (SWE) for use as GND&REF. Methods: A pair of SWEs as GND&REF was tested in nine patients undergoing invasive EEG monitoring. SWE impedances were monitored in two patients and compared to disc electrode impedances. Results: Without maintenance, SWE impedances remained low and stable during the entire recording period (up to 20 days), whereas disc electrodes showed rapid impedance increase όfter the first day. In all nine patients, the consistent and durable integrity of the GND&REF pair of SWE allowed for a good quality EEG recording. No local skin complications were observed. Conclusions: A pair of SWE electrodes provides a GND&REF system that is easy to place, maintain, and provides a high quality recording with long-term stability when couplecl with referential based EEG recording system from invasive electrodes. Significance: A more efficient means of establishing a GND&REF pair during the monitoring of patients with invasive electrodes is described.