Jean G, Charra B, Chazot C, Laurent G
Centre de Rein Artificiel de Tassin, Tassin la Demi-Lune, France.
Kidney Int. 1999 Sep;56(3):1149-53. doi: 10.1046/j.1523-1755.1999.00616.x.
Postdialysis urea rebound (PDUR) is a cause of Kt/V overestimation when it is calculated from predialysis and the immediate postdialysis blood urea collections. Measuring PDUR requires a 30- or 60-minute postdialysis sampling, which is inconvenient. Several methods had been devised for a reasonable approach to determine PDUR-equilibrated Kt/V in short dialysis without the need for a delayed sample. The aim of our study was to compare these different Kt/V methods during the longer eight-hour hemodialysis sessions, and to determine the optimum intradialytic urea sample time that fits best with PDUR.
The study included 21 patients (mean age 71.9 years) who were hemodialyzed for 60+/-60 months at three times eight hours weekly, using bicarbonate dialysate and cellulosic membranes. Blood urea samples were obtained at onset, and then at 17, 33, 50, 66, 75, 80, 85, and 100% of the dialysis session times, after 30 seconds of low flow, and then at 60-minutes postdialysis. All patients had a meal during dialysis. We compared four different formulas of Kt/V [(a) Kt/V-Smye with a 33% dialysis time urea sample, (b) two-pool equilibrated eKt/V, (c) Kt/V-std (Daugirdas-2) obtained with an immediate postdialytic sample, and (d) the different intradialytic urea samples for Kt/V (50, 66, 75, 80, and 85% of dialysis time)] with the equilibrated 60-minute PDUR Kt/V (Kt/V-r-60) formula as the reference method.
The mean PDUR was 17.2+/-9%, leading to an overestimation of Kt/V-std by 12.2%. Kt/V-r-60 was 1.68+/-0.34. Kt/V-std was 1.88+/-0.36 (Delta = 12.2+/-4.8%, r = 0.8). eKt/V was 1.77+/-0.3 (Delta = 5+/-5%, r = 0.96), and Kt/V-Smye was 1.79+/-0.47 (Delta = 5.2+/-14%, r = 0.9). The best time for the intradialytic sampling was 80% (that is, at 6 hr and 24 min). The Kt/V-80 was 1.64+/-0.3 and was best fitted with Kt/V-r-60 (Delta = -1.8+/-8%, r = 0.91). The mean intradialytic urea evolution showed a three-exponential rate, in discrepancy with the two-exponential rate theoretical model.
These results confirm that a significant postdialysis rebound exists in an eight-hour dialysis. An intradialytic urea sample taken at 80% of the total session time permits an estimation of the 60-minute Kt/V-rebound without the necessity of taking a delayed sample, with better accuracy than eKt/V or especially Kt/V-Smye. This may be related to a particular urea kinetics curve on the longer dialysis duration, which needs to be studied further.
当根据透析前和透析后即刻采集的血尿素来计算Kt/V时，透析后尿素反弹（PDUR）是导致Kt/V高估的一个原因。测量PDUR需要在透析后30或60分钟进行采样，这很不方便。已经设计了几种方法来合理确定在短时间透析中无需延迟采样的PDUR平衡Kt/V。我们研究的目的是比较在较长的8小时血液透析过程中这些不同的Kt/V方法，并确定最适合PDUR的透析中尿素采样最佳时间。
该研究纳入了21例患者（平均年龄71.9岁），他们使用碳酸氢盐透析液和纤维素膜，每周进行3次8小时的血液透析，透析时间为60±60个月。在透析开始时、透析过程的17%、33%、50%、66%、75%、80%、85%和100%时间点、低流量30秒后以及透析后60分钟采集血尿素样本。所有患者在透析期间进食。我们将四种不同的Kt/V公式[（a）采用33%透析时间尿素样本的Kt/V-Smye公式，（b）双池平衡eKt/V公式，（c）采用透析后即刻样本获得的Kt/V-std公式（Daugirdas-2），以及（d）不同透析中尿素样本的Kt/V公式（透析时间的50%、66%、75%、80%和85%）]与平衡的60分钟PDUR Kt/V（Kt/V-r-60）公式作为参考方法进行比较。
平均PDUR为17.2±9%，导致Kt/V-std高估12.2%。Kt/V-r-60为1.68±0.34。Kt/V-std为1.88±0.36（差值 = 12.2±4.8%，r = 0.8）。eKt/V为1.77±0.3（差值 = 5±5%，r = 0.96），Kt/V-Smye为1.79±0.47（差值 = 5.2±14%，r = 0.9）。透析中采样的最佳时间是80%（即6小时24分钟）。Kt/V-80为1.64±0.3，与Kt/V-r-60拟合最佳（差值 = -1.8±8%，r = 0.91）。透析中尿素平均变化显示出三指数速率，与双指数速率理论模型不一致。
这些结果证实了在8小时透析中存在显著的透析后反弹。在总透析时间的80%时采集透析中尿素样本可估算60分钟的Kt/V反弹，无需延迟采样，准确性优于eKt/V或特别是Kt/V-Smye。这可能与较长透析时间下特定的尿素动力学曲线有关，需要进一步研究。
