Near‐infrared tissue oximetry and digital image analysis: quantification of renal ischaemia in real time during partial nephrectomy

What’s known on the subject? and What does the study add? There is little known on how to objectively measure renal ischemia during partial nephrectomy. This study clemonstrates two potentially useful methods to measure renal ischemia during partial nephrectomy. OBJECTIVE • To determine the feasibility of using near-infrared tissue oximetry (TO) and digital image analysis for assessing renal function and to quantify local renal ischaemia in a porcine model. MATERIALS AND METHODS • Tissue oximetry was performed and red/blue (R/B) colour ratios were determined on renal units of Yorkshire swine. • Interval measurements were taken before clamping the renal hilum, during warm ischaemia, and after unclamping using a ViOptix T.OxTM Tissue Oximeter and Matlab® digital image analysis. • Matlab software analysed images from the laparoscopic camera and determined an R/B ratio to track renal ischaemia. • The tissue oximeter used direct infrared light and was placed adjacent to the kidney parenchymal surface. • The data were divided into preclamp, clamp and post-clamp, and compared between methodologies. RESULTS • The R/B ratio showed a higher rate of change compared with TO during clamp time in both the 15-min experiment (R/B = 96.0 vs. TO = 52.1 unit/reference) and the 30-min experiment (R/B = 97.6 vs. TO = 45.9). • The R/B ratio showed a higher rate of change compared with TO at 1 min after clamping in the 15-min experiment (R/B = 80.1 vs. TO = 12.4). • Both detection devices showed similar changes in pre- and post-clamp measurements in the 15- min experiment (R/B = 1.6 vs. TO = 3.8) and the 30-min experiment (R/B = 4.7 vs. TO =−4.5). • In the 30-min experiment the R/B ratio showed a significant difference between preclamp, clamp, and post-clamp states (P= 0.026). CONCLUSIONS • Both TO and digital image analysis were able to calculate an ischaemic drop in tissue oxygen saturation during periods of acute renal ischaemia. • The findings suggest that the R/B ratio observed during histogram analysis shows a greater sensitivity compared with TO in quantifying renal ischaemia.