Paradoxical alteration of indocyanine green concentration in bile and the visibility of the intra-operative fluorescence cholangiography in pigs

BACKGROUND: A significant difference exists between the reported optimal timing of indocyanine green (ICG) injection during fluorescence cholangiography and ICG dissipation time from the serum. There are no reports on alterations in ICG concentration in biliary fluid over time. Herein, we measured the concentration of ICG and the fluorescence intensity ratio between the common bile duct (CBD) and liver, which was recognized as a parameter of the visibility of the CBD. MATERIALS AND METHODS: ICG (0.05 mg/kg) was injected intravenously into female pigs (n = 7). Afterwards, the fluorescence of the CBD and liver was detected at 30 min, 2 h, and 4 h. Biliary fluid was collected from cannulated CBD tubes. The fluorescence intensity was measured using captured images and calculated using the ImageJ image-processing program. ICG concentration was measured using spectrophotometry and compared using an analysis of variance test. RESULTS: Biliary ICG concentrations at 30 min, 2 h, and 4 h were 92.07 ± 27.72 μg/mL, 37.14 ± 9.76 μg/mL (p < 0.05 vs. 30 min), and 13.91 ± 5.71 μg/mL (p < 0.05 vs. 30 min), respectively; p < 0.01. The CBD/liver fluorescence intensity ratios at 30 min, 2 h, and 4 h were 1.25 ± 0.72, 2.39 ± 1.28 (p < 0.05 vs. 30 min and 4 h), and 3.38 ± 1.73 (p < 0.05 vs. 30 min and 2 h), respectively. CONCLUSIONS: The ICG biliary concentration was highest at 30 min, whereas the CBD/liver fluorescence intensity ratio was highest at 4 h. Decreasing the fluorescence intensity of the liver may be an important approach for improving the visualization of the CBD during fluorescence cholangiography. INSTITUTIONAL PROTOCOL NUMBER: PE/EA/491–5/2020.