The impact of nitroglycerine and volume on gastric tube microperfusion assessed by indocyanine green fluorescence imaging

Figures

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  Figure 1. Macroscopic and fluorescent image of the gastric tube. The left picture (a) shows the macroscopic picture of the gastric tube. Three regions of interest (ROI) are marked: The prepyloric region (D3), the corpus (D2), and the tip (D1). The right picture (b) shows the associated fluorescence angiographic image of the gastric tube with the same marked ROIs.

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  Figure 2. Experimental setting. Three groups were formed from a total of 21 animals: A control group (n = 7), a group with continuous infusion of nitroglycerine (n = 7), and a group with hypervolemia. In each animal, a gastric tube was created and divided into three segments: Gastric fundus (D1), gastric corpus (D2), and prepyloric region (D3). Various measurements were carried out at three predefined times (T1: hypotension, T2: normotension; T3: hypertension): Indocyanine green fluorescence imaging (ICG-FI) with the calculation of slope of fluorescence intensity (SFI), background subtracted fluorescence intensity (BSFI) and time to slope (TTS), application of fluorescent microspheres, continuous measurement of the hemodynamics, transit time flow measurement (TTFM) of the right gastroepiploic arteria and tissue oxygenation (tPO2). MAP mean arterial blood pressure.

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  Figure 3. Figure shows a time-dependent fluorescence intensity curve and a schematic presentation for calculating the quantification parameters SFI, BSFI, and TTS. TTS defines the time between Indocyanine green (ICG) administration and the first fluorescence signal. SFI represents the maximal slope of the curve. For the calculation of BSFI, the initial fluorescence intensity before injection of ICG is subtracted from the peak fluorescence intensity.

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  Figure 4. Slope of fluorescence intensity (SFI) values of all groups (1 = control, 2 = nitroglycerine, 3 = volume) are shown in logarithmic form in boxplots at each measurement time (1 = Hypotension, 2 = Normotension, 3 = Hypertension) in each areal (1 = tip, 2 = corpus, 3 = prepyloric). Circles (°) represent mild outliers and asterisks (*) represent extreme outliers. The y-axis shows a logarithmic representation of the SFI values while the other axes represent categorical variables. SFI represents the maximal increase of the time-dependent fluorescence intensity induced by the first wave of the Indocyanine green (ICG), which passes the capillaries of the gastric tissue. SFI-values in groups two and three were significantly lower in areal 2 and 3 compared to the control group (p < 0.001). SFI-values in areal 1 showed no significant differences between all groups. In group 3, hypertension resulted in decreasing SFI indicating impaired perfusion.

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  Figure 5. Background subtracted peak fluorescence intensity (BSFI) values of all groups (1 = control, 2 = nitroglycerine, 3 = volume) are shown in logarithmic form in boxplots at each measurement time (1 = Hypotension, 2 = Normotension, 3 = Hypertension) in each areal (1 = tip, 2 = corpus, 3 = prepyloric). Circles (°) represent mild outliers and asterisks (*) represent extreme outliers. The y-axis shows a logarithmic representation of the BSFI values while the other axes represent categorical variables. BSFI represents the difference in the initial intensity value before the injection of ICG was subtracted from the peak fluorescence intensity during the first passage of the dye through the gastric tube. Across all groups, areal 3 showed lower BSFI-values in group 3 compared to group 1 (p < 0.05). Group 2 showed similar trends, which were not statistically significant.

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  Figure 6. Transit time flow measurement (TTFM) at the right gastroepiploic artery shown as boxplots. Circles (°) represent mild outliers and asterisks (*) represent extreme outliers. The flow is increasing with increasing median arterial blood pressure. The substitution of nitroglycerine is not associated with changes in flow. Hypervolemia shows improved flow at normotension compared to hypo- and hypertension. There were no significant differences between the groups and the time of measurement.

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  Figure 7. Tissue oxygenation of all groups shown as boxplots. Circles (°) represent mild outliers and asterisks (*) represent extreme outliers. In all groups, the tip shows significantly reduced tissue oxygen partial pressure. In the control group, tissue oxygenation is highest in the corpus. Administration of nitroglycerine results in no significant differences between corpus and prepyloric regions. Hypervolemia also shows the highest oxygenation levels in the corpus. There were no statistically significant changes between the measurement times (hypotension, normotension, and hypertension, respectively).