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with eventual full recovery of function [6], but with longer periods of warm ischaemia there is significant immediate functional loss with either incomplete or no delayed recovery of renal function [5]. In humans, 30 min is the maximum tolerable period of warm ischaemia before permanent damage ensues.Hypothermia is the technique most commonly used to protect the kidneys from ischaemic damage. Lowering renal temperature reduces energy-dependent metabolic activity of the cortical cells, leading to decreased oxygen consumption and reduced ATP breakdown. A negative effect of hypothermia is inactivation of the sodiumpotassium pump at the cellular level, which ultimately allows salt and water to enter the cell. These effects are completely reversible at temperatures of > 4 ° C. For practical purposes, a uniform temperature of 20-25 ° C is adequate to maintain renal function even after 3 h of arterial occlusion.

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OBJECTIVE To compare the relative ease of manipulation around a calyceal model in the hands of experienced ureteroscopists of four flexible ureteroscopes (FUs), as new‐generation FUs provide exaggerated active deflection to facilitate intrarenal manipulation. SUBJECTS AND METHODS Four FUs of <7.5 F were tested: the FlexVision U‐500 (SF) (Stryker Endoscopy, San Jose, CA, USA), the Dur‐8 Elite (D8E) (ACMI, Southborough, MA, USA), the Viper (Richard Wolf Medical Instruments, Vernon Hills, IL, USA) and the URF‐P3 (Olympus Surgical, Orangeburg, NY, USA). Eight experienced ureteroscopists, each with a minimum of 100 flexible ureteroscopies over the preceding 3 years, assessed the FUs. The Mediskills calyceal model represents a moderately hydronephrotic collecting system, with a renal pelvic width of 2 cm, infundibular widths of 1 cm and infundibular lengths of 2 cm. The middle calyx infundibular angle was 80° and the lower calyx infundibular angle was 100°. The model does not allow for significant passive secondary deflection. The surgeons manoeuvred systematically around a four‐point course, from the pelvi‐ureteric junction, to anterior lower calyx, to anterior middle calyx, to posterior lower calyx, to posterior middle calyx, touching a metal sensor with an fulguration electrode, to trigger an automated signal at each calyx. The order of FU used by each surgeon was randomized. Each surgeon performed the course twice with each FU, ending with the first FU they started with, to diminish the impact of ‘learning the course’. RESULTS There were significant differences in the mean (sd) total time for manipulation through the four‐point course, for the Viper, SF, D8E and URF‐P3, at 29 (11), 37 (23), 38 (20) and 50 (24) s, respectively (P = 0.034). The URF‐P3 took longer to reach the posterior lower pole, at 18.1 (14.5) s than the Viper, SF and D8E, at 6.3 (2.8) (P = 0.004), 6.6 (3.3) (P = 0.008) and 7.7 (4.9) (P = 0.008), respectively. The Viper was quicker to reach the posterior middle pole, at 7.3 (4.0) s, than the URF‐P3, SF and D8E, at 14.9 (13.1) (P = 0.036), 14.7 (14.3) (P = 0.056) and 12.7 (14.0) s (P = 0.115), respectively. Subjectively, six of eight endoscopists stated that the Viper was the better FU for ease of manipulation, while five of eight stated that the URF‐P3 was the most difficult. Notably, all eight endoscopists had more clinical experience with the URF‐P3 than with the other three FUs tested. CONCLUSIONS In a model of a moderately hydronephrotic kidney with long infundibulum and limited ability to perform passive secondary deflection, FUs with exaggerated active deflection outmanoeuvred the URF‐P3. The Viper was better for manipulation in the hands of experienced endoscopists.

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