Gastric impedance spectroscopy in elective cardiovascular surgery patients

Impedance spectroscopy has been proposed as a method of monitoring mucosal injury due to hypoperfusion and ischemia in critically ill patients. The present study characterizes human gastric impedance spectral changes under gastric hypoperfusion in patients undergoing cardiovascular surgery, and evaluates spectral differences between patients with no evidence of gastric ischemia and complications, and patients who developed ischemia and complications. Cole and Kun parameters were calculated over time to characterize changes as tissue injury progresses. Gastric ischemia was determined by air tonometry. Impedance spectroscopy spectra were obtained from 63 cardiovascular surgery patients. The recorded spectra were classified into three groups: group 1 for patients without ischemia or complications, group 2 for patients with a short period of ischemia (less than 2 h) and group 3 for patients with more than 4 h of gastric ischemia and complications. Two distinct dispersion regions of the spectra centered at about 316 Hz and 215 kHz become clearer as tissue damage develops. The average spectrum in group 3 shows a significant difference in tissue impedance at all frequencies relative to group 1. The parameters obtained for human gastric tissue show significant changes that occur at different times and at different frequencies as ischemia progresses, and could be correlated with patient outcome. This confirms our hypothesis that hypoperfusion and ischemia cause evident changes in the impedance spectra of the gastric wall. Therefore, this technology may be a useful prognostic and diagnostic monitoring tool.