Technical Requirements for Electroencephalography in the Operating Area

Abstract

Under standard conditions, the electric brain activity recorded from the scalp has a potential difference of about 10–100 µV, occasionally up to 300 µV, with a frequency of approximately 0.5–40 Hz; it thus encompasses a considerable dynamic range. This fact and the necessity to suppress any interfering voltage with a possibly high amplitude demand high standards of quality and sensitivity of EEG amplifiers. Therefore, in clinical neurophysiology, EEG recordings are performed in specially fitted and shielded rooms. In addition to comfortably fitted chairs for a sitting or a reclining position —so as to diminish biological artefacts during the tracing —these rooms have special electric equipment, mainly a Faraday cage, to eliminate interfering electric fields. To profit from EEG recordings in anesthesiology, the highly sensitive equipment has to be moved into the operating rooms, where there are a great number of sources of interference that have to be tolerated. Of course, the electric shielding usually used in the EEG laboratory is absent in the operating room. Redesigning the operating rooms is usually not possible for financial reasons. Since the advantage of continuous EEG recording during anesthesia is of immense value, this chapter discusses means of obtaining EEG recordings despite the above-mentioned obstacles ([3] Faulconer and Bickford 1960; Brechner and Walter 1962; SADOVEetal. 1967).