165 Real-time quantification of LSCI during intestinal laparoscopic surgery differences, consistent with previous studies 12, 16-18. Although there was a clear distinction between areas, all LSPUs continued to decrease over time. In ischemic tissue, this decline is due to diminished flow post-ligation of feeding arteries, restricting blood inflow. Conversely, in well-perfused tissue, intestinal perfusion restriction may result from systemic illness response following prolonged ischemia. In contrast to the LSPUs in ischemic tissue, we surmised that lactate levels decreased after the first hour. This may be attributed to small overlapping vessels on the serosa, originating from a more adequately perfused intestinal segment, facilitating a modest collateral reperfusion effect 33. This phenomenon may also explain a marginal surge in systemic lactate levels, as collateral vessels transport lactate into the systemic circulation. Additionally, oxygen deprivation from devascularization induces anaerobic fuel consumption, initiating fermentative glycolysis and an initial rise in lactate within ischemic tissue 34. Compromised metabolic flux in ischemic tissue may deplete glucose supplies, reducing cellular energy consumption and halting lactate formation. Moreover, despite commonly perceived as a waste product, lactate can serve as an alternative fuel source within the tricarboxylic acid (TCA) cycle 35. Based on our current findings, LSPUs above 69 AU indicate well-perfused tissue, with high sensitivity and specificity, highlighting the robustness of LSCI for perfusion visualization. Nevertheless, extensive additional research is required to extrapolate the use of a cut-off in LSCI in different tissues and humans. The cut-off value for lactate was primarily determined to validate the perfusion areas derived from the PerfusiX-Imaging® device. Values exceeding 3.8 mmol/L appeared indicative of ischemia. Although a well-defined cut-off value for Landrace pigs exists, our results aligned with existing literature, with systemic lactate levels typically below 2.0 mmol/L in a neutral state, while levels exceeding the determined cut-off value were observed in ischemic tissue 12, 33, 36-39. All evaluators observed clear differentiation between adequately and inadequately perfused tissue. Agreement in identifying watershed regions ranged from moderate to substantial, with no significant difference between experts and unexperienced physicians. However, observers did encounter challenges in interpreting images lacking a clear-cut watershed line. This scenario occurred in case of a more gradual transition between well-perfused and poorly perfused tissue. Consequently, images displaying such transitions exhibited decreased inter-observer agreement, stipulating the importance of quantitative assessment methods to aid in the identification of viable and non-viable tissue. In contrast to fluorescence angiography, LSCI does not require any pharmaceuticals or dyes, reducing risks of adverse reactions as seen with ICG 40. Moreover, absence of these substances eliminates the need for timing and dosing calculations and facilitates repeated measurements without the interference of wash-out effects or residual signals 41, 42. Quantifying ICG poses challenges, as it demands the standardization of numerous factors to obtain meaningful quantitative data 20. While maximizing standardization in measurements is essential across 8
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