Intra-operative and early post-operative cortical resistive indices in renal transplantation: Representative values according to graft function and time of scan

Intra-operative ultrasound during renal transplantation identifies technical abnormalities allowing immediate surgical correction as required. Cortical resistive indices (RIs) assess graft perfusion and are now measured intra-operatively. The aim of this study was to evaluate RIs intra-operatively, and to 30 days post-operatively. RIs in consecutive single renal grafts in adults were analysed from 246 grafts scanned intra-operatively, on day 1 post-operatively and subsequently according to physician preference, and 125 grafts scanned intra-operatively to day 30 post-operatively according to a formal protocol. There was delayed graft function (DGF) in 125 grafts. The mean(±sem) intra-operative RI of 0.599(±0.009) was significantly lower (p<0.001) than post-operatively, with the highest RIs on days 3 and 7. RIs on day 30 were similar to day 1. RIs in grafts with function were significantly lower than grafts still requiring dialysis. Mean(±sem) cortical RIs on post-operative days 1, 3, 7 and 30 in functioning grafts were 0.662(±0.005), 0.712(±0.008), 0.703(±0.007) and 0.689(±0.006) respectively, and in grafts still requiring dialysis 0.721(±0.010), 0.780(±0.010), 0.793(±0.011) and 0.751(±0.034). The intra-operative RI predicted DGF (AUROC 0.774) as effectively as donor status (live/deceased) (AUROC 0.767). For deceased donor grafts, intra-operative RI was a more effective predictor (AUROC 0.710) than type of donor (DCD/DBD) (AUROC 0.610). Intra-operative RIs are significantly lower than post-operatively and are indicative of post-operative graft function. Post-operative RIs in non-functioning grafts are consistently higher than in functioning grafts. Observed RIs differ according to the post-operative day of scan, which therefore should also be reported.