Small intestinal ischemia and reperfusion - bioimpedance measurements.

Objective: Trans-intestinal bioimpedance measurements have previously been used to investigate changes in electrical parameters during 6 h of ischemia in the small intestine. Knowledge is lacking regarding the time course of trans-intestinal bioimpedance parameters during reperfusion. As reperfusion is an important part in the clinical treatment of intestinal ischemia, we need to know how it affects the bioimpedance measurements. Approach: We performed bioimpedance measurements, using a two-electrode setup on selected segments of the jejunum in 15 pigs. A controlled voltage signal was applied while measuring the resulting current. In each pig, five or six 30 cm segments of the jejunum were made ischemic by clamping the mesenteric arteries and veins creating segments with ischemia from 1-16 h duration. Reperfusion was initiated at selected time intervals of ischemia, and measured for 5-15 h afterwards. Main results: The tan delta parameter (loss tangent) was different (p < 0.016) comparing ischemic and control tissue for the duration of the experiment (16 h). Comparing the control tissue 30 cm from the ischemic area with the control tissue 60 cm from the ischemic tissue, we found that the mean tan d amplitude in the frequency range (3900-6300 Hz) was significantly higher (p < 0.036) in the proximal control after 10 h of experiment duration. After reperfusion, the time development of tandm (loss tangent maximum over a frequency range) amplitude and frequency overlapped and periodically increased above the tandm in the ischemic intestine. Dependent on the ischemic duration pre-reperfusion, the initial increase in tan d stabilizes or increases drastically over time, compared to the tan d amplitude of the ischemic tissue. Significance: As during ischemia, the electrical parameters during reperfusion also follow a characteristic time-course, depending on the ischemic exposure before pre-reperfusion. The temporal changes in electrical parameters during small intestinal ischemia followed by reperfusion provides important information for assessment of tissue injury.