Changes in chest electrode impedance

The Prehospital Defibrillation Program in Singapore has in some cases shown a lower amplitude of ventricular fibrillation (VF) than considered the nor m. The electrode skin impedance (ESI) refers to the skin impedance determin ed between two electrodes placed at specific positions on the body surface. The objective of this prospective study was to measure the ESI of patients at 5 Hz and 2 kHz frequencies, and assess its change with time from the ap plication of electrodes, the difference between the ESI at two different se ts of electrode placement positions, and correlation with patient factors. Patients who were 25 years or older and not critically ill had their ESI me asured with a modified Heart-Save 911 defibrillator, using signal frequenci es at 5 Hz and 2 kHz, at 10 seconds, 1 and 2 minutes after electrodes appli cation. Two sets of positions were used; position 1 where an electrode is p laced in the right subclavicular region and another just lateral to the ape x beat on the left and position 2, which represents the mirror-image of pos ition 1, Thirty-six each of men and women patients were studied. The mean a ge and weight were 59.9 +/- 13.5 years and 56.8 +/- 24.1 kg respectively. T here was no significant correlation between the ESI and patients' body weig ht or sex. However, there was a significant decrease in the ESI with time f rom application of electrodes at both positions (P < .05) with the two diff erent frequencies. The ESI was lower when measured at tower frequencies and higher when taken at higher frequencies, but there was no statistically si gnificant difference between the two mirror image positions used. Thus, wit h lower frequency, the electrocardiogram amplitude of VF recorded on the au tomated external defibrillator could be enhanced.