Gastric impedance spectroscopy in elective cardiovascular surgery patients

Abstract

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.

Gastric Tissue Damage Analysis Generated by Ischemia: Bioimpedance, Confocal Endomicroscopy, and Light Microscopy

“…We proposed that bioimpedance and particularly gastric reactance is an early indicator of ischemia and we developed some studies that confirm the prognostic and diagnostic value of these measurements [20, 21]. However, before we may advocate the clinical use of this technology we need to first answer the following questions: (1) Can we quantify oedema and tissue damage from impedance parameters?, (2) Can we use this information to improve patient management and treatment?…”

Gastrointestinal ischemia monitoring through impedance spectroscopy as a tool for the management of the critically ill

“…Gastric reactance shows high sensitivity to predict outcome, compared with some hemodynamic and regional perfusion variables. 25,26 Low-frequency gastric reactance, X L , had a significant predictive value of postoperative persistent shock requiring more than 48 h of vasopressors and associated complications, before, during, and after surgery (P < 0.05) (see Table 1). Patients with a high reactance (X L > 26) before surgery had a significantly higher incidence of complications, higher mortality, and more days in the intensive care unit (ICU) than patients with a low reactance (X L < 13).…”

“…Our research group reported a relationship between bioimpedance changes with tissular damage level generated by ischemia by means of confocal endomicroscopy and light microscopy 21 ; also two animal models of shock were made, one to monitor ischemic injury of the intestinal mucosa in a hemorrhagic shock model in rabbits, 22 other to show that combined splanchnic tissue indicators have the potential of been used as complementary tools for guiding a treatment in septic shock. 23 Finally, we developed some human studies to evaluate the clinical significance of the impedance measurements: in healthy volunteers, 24 in elective cardiovascular surgery patients, [25][26][27] and the last one in general critically ill patients. 28 This document attempts to summarize our work to date, showing the importance of gastric ischemia monitoring and main animal and human results.…”

“…Our device ( Figure 10) has been shown to provide reproducible measurements under clinical conditions that contain relevant information on the patient's progress. 25,26,28 The impedance spectra also provide a distinctive shape or fingerprint that will be effective to identify improper placement, excessive movement artifact or noise and device failures, and therefore improve our confidence in the measurement. The challenge was to reduce the dimensionality of the complex measurements to one or two simple variables that were robust and easy to interpret so that this system could be used effectively in clinical practice.…”

Algorithm for Characteristic Parameter Estimation of Gastric Impedance Spectra in Humans

“…Along with the technique, an impedance spectroscopy probe and nasogastric tube ISP/NGT [5] allows the direct acquisition of an electric impedance spectrum of the mucosa, which can be used to identify and continuously monitor the level of tissue damage. N Our research group recently reported that hypoperfusion and ischemia cause changes in the impedance spectra of the gastric wall in cardiovascular surgery patients [6], proposing that this technology may be a useful prognostic and diagnostic monitoring tool.…”