THE THERMAL PERFORMANCE OF ELECTROSURGICAL DISPERSIVE ELECTRODES

JOHN ANTHONY PEARCE, Purdue University

Abstract

Major variables affecting the thermal performance of electrosurgical dispersive electrodes include: the geometry of the electrode, the anatomical substructure of the tissue to which it is applied, the intensity and duration of the current flow, and regional blood flow at the electrode site. These variables were investigated in experiments on volunteer subjects, theoretical temperature rise predictions, and on phantom structures. A theoretical model of the electrode/tissue structure was assembled from electrical and thermal field theory. A physical phantom was constructed which duplicated the calculation geometry to verify the accuracy of the predicted surface temperature distributions. The model included layered electrical media of differing properties and arbitrarily shaped and located conductors. Test models were designed to simulate the effects observed on the human subjects. Tests on commercially-available dispersive electrodes showed temperature rises between 1 and 6(DEGREES)C at a current of 700 mA(rms) for 60 seconds (500 KHz sine wave)--a delivered energy in excess of values expected in surgical procedures. Females consistently exhibited a higher temperature rise than males under the same test conditions owing to the difference in skin substructure. Measurements on pig skin established that the threshold temperature for skin damage was in the neighborhood of 45(DEGREES)C--approximately a 12(DEGREES)C rise over normal skin temperature. This suggests that a 5 to 6(DEGREES)C temperature rise is a probable maximum safe limit for a dispersive electrode. Experiments on humans indicated that increasing the perimeter and smoothing the sharp corners of an electrode improves its thermal performance when all other factors are kept constant. Good agreement was obtained between the calculated and measured surface temperature contours.

Degree

Ph.D.

Subject Area

Electrical engineering

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