To the Editor :

Ex vivo normothermic machine perfusion (NMP) was introduced into clinical practice recently,1 and there is ongoing interest in its utility in renal transplantation. In a pilot series, 1 hour of NMP after a period of static cold storage reduced delayed graft function when compared to static cold storage alone.2 This led to the establishment of the first multi‐center randomized clinical trial of NMP, which is ongoing.3

Our NMP perfusion system is based on existing cardiopulmonary bypass technology using the principles of extracorporeal membrane oxygenation. The perfusion circuit consists of an organ chamber, a centrifugal pump, a membrane oxygenator, a heat exchanger, and a venous reservoir. The renal artery is perfused with an oxygenated red cell–based solution maintained at normal body temperature and anticoagulated with 3000 units of heparin. The ureter is catheterized to allow an accurate measurement of urine output. Here we report the use of a double‐J ureteric stent to improve the collection and measurement of urine output during NMP.

We have previously catheterized the donor ureter using a soft narrow gauge Nelaton catheter (Braun), but there are a number of problems with this approach. First, placement of Nelaton catheters is commonly associated with the development of hematuria during NMP. This is because in a highly anticoagulated system, even very slight trauma to the renal pelvis from the tip of the Nelaton catheter causes bleeding. Second, it is difficult to be sure that the tip of the Nelaton catheter is correctly placed in the renal pelvicalceal system. This can lead to frequent re‐positioning and further trauma to the urothelium. Third, normal peristalsis is re‐established during NMP and this leads to migration of the Nelaton catheter tip even if the catheter is ligated at the distal ureter.

In response to these problems we now routinely use a 5 French transplant ureteric double‐J stent (Figure 1). This can be placed easily without the use of a guide‐wire to avoid unnecessary trauma. Double‐J stents are designed to be atraumatic and self‐retaining, and the dependent distal loop of the double‐J stent sits well in the urine collection receptacle. We have found that the use of a double‐J stent virtually eliminates hematuria during NMP. Once placed correctly, the double‐J stent does not require any further manipulation and provides accurate monitoring of urine output. There are no additional costs associated with the use of a double‐J stent, as it remains sterile throughout NMP and can subsequently be used during the ureteroneocystotomy step of the transplant operation.

致编辑：

最近，离体常温机器灌注 (NMP) 被引入临床实践，1并且人们对其在肾移植中的效用​​持续感兴趣。在试验系列中，与单独的静态冷藏相比，经过一段时间的静态冷藏后 1 小时的 NMP 减少了延迟的移植物功能。2这导致建立了第一个正在进行的 NMP 多中心随机临床试验。3个

我们的 NMP 灌注系统基于现有的体外膜氧合原理的体外循环技术。灌注回路由器官室、离心泵、膜氧合器、热交换器和静脉储液器组成。肾动脉灌注含氧红细胞溶液，保持正常体温，并用 3000 单位肝素抗凝。输尿管插入导管以准确测量尿量。在这里，我们报告了使用双 J 输尿管支架来改善 NMP 期间尿量的收集和测量。

我们以前使用软窄规格 Nelaton 导管 (Braun) 对供体输尿管进行导管插入，但这种方法存在许多问题。首先，放置 Nelaton 导管通常与 NMP 期间出现血尿有关。这是因为在高度抗凝的系统中，即使 Nelaton 导管尖端对肾盂造成非常轻微的创伤也会导致出血。其次，很难确定 Nelaton 导管的尖端是否正确放置在肾盆腔系统中。这可能导致频繁重新定位和进一步损伤尿路上皮。第三，在 NMP 期间重新建立正常蠕动，这导致 Nelaton 导管尖端移动，即使导管结扎在远端输尿管。

针对这些问题，我们现在常规使用 5 French 移​​植输尿管双 J 支架（图 1）。这可以在不使用导丝的情况下轻松放置，以避免不必要的创伤。双 J 支架设计为无创伤和自我固定，双 J 支架的依赖远端环很好地固定在尿液收集容器中。我们发现使用双 J 支架几乎可以消除 NMP 期间的血尿。一旦正确放置，双 J 支架不需要任何进一步的操作，并可以准确监测尿量。使用双 J 支架不会产生额外费用，因为它在整个 NMP 过程中保持无菌状态，随后可以在移植手术的输尿管膀胱切开术步骤中使用。