Eloot Sunny, Dhondt Annemieke, Vierendeels Jan, De Wachter Dirk, Verdonck Pascal, Vanholder Raymond
Institute of Biomedical Technology, Ghent University, Campus Heymans--Block B, De Pintelaan 185, 9000 Gent, Belgium.
Nephrol Dial Transplant. 2007 Oct;22(10):2962-9. doi: 10.1093/ndt/gfm356. Epub 2007 Jun 13.
The Genius single-pass batch system, using a closed dialysate container, is increasingly applied for dialysis treatment. Although fluid separation between fresh and spent dialysate is maintained in the container during standard dialysis, dialysate mixing may occur under certain clinical conditions. An in vitro study showed that differences in dialysate temperature and solute content between fresh and spent dialysate determine the occurrence and moment of dialysate mixing.
To better understand the maintenance of separation of fresh and spent dialysate in the prevention of mixing, a mathematical model of the 75 l Genius container was developed and the general fluid, mass and heat transfer equations were solved, simulating a dialysis session of 300 min with 1 g/l urea as starting 'blood' urea concentration and 36.2 degrees C starting dialysate temperature. Boundary and initial conditions were chosen according to two different strategies applied in previous in vitro tests, with spontaneous cooling of the reservoir on the one hand and heating of the spent dialysate to maintain an equal temperature as the fresh dialysate on the other.
Our simulation data show that dialysate inside the container is cooling down near the container wall in both scenarios and near the central glass tube in the setup with spontaneous cooling. In the setup with heating of spent dialysate, the upper layers are heated near the central tube. Since density stratification is maintained at each time point, solutes will rise towards warmer zones. This is halfway between the container axis and wall for spontaneous cooling and, even to a larger extent, near the central tube for simulations with heated spent dialysate. Hence, the contaminated volume in the case of heating is much larger than theoretically supposed.
These computer simulations unravel temperature and concentration distribution inside the container, offering insight into the complicated mixing phenomenon and indicate that temperature is a major impacting factor.
采用封闭透析液容器的Genius单程批量系统越来越多地应用于透析治疗。尽管在标准透析过程中容器内新鲜透析液和用过的透析液之间保持了液体分离，但在某些临床情况下仍可能发生透析液混合。一项体外研究表明，新鲜透析液和用过的透析液之间的温度和溶质含量差异决定了透析液混合的发生和时刻。
为了更好地理解新鲜透析液和用过的透析液分离以防止混合的维持情况，建立了75升Genius容器的数学模型，并求解了一般的流体、质量和传热方程，模拟了以1克/升尿素作为起始“血液”尿素浓度和36.2摄氏度作为起始透析液温度的300分钟透析过程。根据先前体外试验中应用的两种不同策略选择边界条件和初始条件，一方面储液器自然冷却，另一方面将用过的透析液加热以保持与新鲜透析液相同的温度。
我们的模拟数据表明，在两种情况下，容器内的透析液在容器壁附近以及自然冷却设置中靠近中央玻璃管处均在降温。在加热用过的透析液的设置中，上层在中央管附近被加热。由于在每个时间点都保持密度分层，溶质将向较温暖的区域上升。在自然冷却情况下，这发生在容器轴线与壁的中间位置，而在加热用过的透析液的模拟中，甚至在更大程度上发生在靠近中央管的位置。因此，加热情况下的污染体积比理论假设的要大得多。
这些计算机模拟揭示了容器内的温度和浓度分布，深入了解了复杂的混合现象，并表明温度是一个主要影响因素。
