Effects of skin temperature on skin-electrode impedance: measurements at high direct current density

Skin-electrode impedance was determined between two disposable electrodes 5 cm apart on the volar skin of the forearm in 20 patients during cooling on cardiopulmonary bypass. Measurements were made using a constant direct current pulse of 200 microseconds duration, at a current density of 25.6 mA cm-2. The mean inter-electrode resistance was 1.11 k omega, and the mean inter-electrode capacitance was 33.3 nF. In 19 patients there was no change in the inter-electrode resistance or the inter-electrode capacitance with changes in skin temperature from 27.5 to 36.0 degrees C. In one patient the inter-electrode resistance increased from 1.71 k omega at 35 degrees C to 1.94 k omega at 31.0 degrees C, while the inter-electrode capacitance increased from 19.6 to 26.6 nF. We conclude that temperature effects on the impedance of the stimulus electrodes are not responsible for the observed failure of evoked electromyography during clinical monitoring of neuromuscular function.