A Novel Ice Pillow Cooling Technique Reduces Renal Rewarming During Simulated Vascular Anastomosis: An Ex Vivo Study Using Human Renal Allografts

Background: Preservation of renal hypothermia during vascular anastomosis remains a critical yet insufficiently optimized aspect of kidney transplantation. Rewarming during the second warm ischemic period increases metabolic activity and may exacerbate ischemia–reperfusion injury. Maintaining graft temperatures below the 15–18 °C metabolic threshold during implantation is associated with improved graft preservation, yet more than 80% of grafts exceed this threshold within 20 min under standard conditions. This study evaluated the thermal performance of a novel cooling adjunct, the Ice Pillow, in limiting renal rewarming under simulated ex vivo transplant conditions. Methods: Twelve human renal allografts (six donor pairs) were studied in a controlled laboratory setting following hypothermic machine perfusion. Within each donor pair, kidneys were randomly assigned to the Ice Pillow group or the Control group. Core temperature was measured using an intra-pelvic thermocouple probe, while surface temperature was assessed with a handheld infrared thermometer. Kidneys in the Ice Pillow group were positioned on a thin gauze pouch filled with ice slush. Control kidneys were rewarmed in a simulated body cavity at 30–32 °C. Temperature recordings were obtained at one-minute intervals over 40 min. Rewarming slopes were compared using donor-paired analysis. Longitudinal temperature trajectories were analyzed using a linear mixed-effects model accounting for repeated measurements within kidneys. Agreement between core and surface measurements was evaluated using Bland–Altman analysis. Results: The Ice Pillow reduced the rate of renal rewarming by 56.4% compared with donor-paired controls (0.261 ± 0.057 °C/min vs. 0.599 ± 0.066 °C/min; mean donor-paired difference 0.338 °C/min; 95% CI, 0.237–0.440; t(5) = 8.56, p < 0.001). Linear mixed-effects modelling demonstrated progressive thermal separation between groups, with Control kidneys estimated to be 4.28 °C warmer at 10 min (95% CI, 3.35–5.22; p < 0.001) and 10.44 °C warmer at 40 min (95% CI, 7.88–12.99; p < 0.001). Bland–Altman analysis of core–surface agreement demonstrated a mean bias of −0.51 °C with 95% limits of agreement of −6.46 °C to 5.43 °C, indicating that surface thermometry followed the general direction of core temperature change but demonstrated wide limits of agreement, indicating the two methods are not interchangeable. Conclusions: In this ex vivo model, the Ice Pillow substantially attenuated renal rewarming compared with unassisted controls. Whether this thermal effect translates into improved graft function requires prospective clinical evaluation.