Supplementary Material for: Predictions of Serum Phosphate Concentration During CRRT Using a Steady State Mass Balance Model

Introduction: Hypophosphatemia is common during continuous renal replacement therapy (CRRT), but serum phosphate levels can potentially be maintained during treatment by either intravenous phosphate supplementation or addition of phosphate to renal replacement therapy (RRT) solutions.

Methods: We developed a steady state phosphate mass balance model to assess the effects of CRRT dose on serum phosphate concentration when using both phosphate-free and phosphate-containing RRT solutions, with emphasis on low CRRT doses.

Results: The model predicted that measurements of serum phosphate concentration prior to (initial) and during CRRT (final) together with clinical data on CRRT dose, treatment duration and phosphate supplementation can determine model patient parameters, that is, both the initial generation rate and clearance of phosphate prior to CRRT. Model parameters were then calculated from average patient data reported in several previous publications with a standard or high CRRT dose. Using representative model parameters for typical patients, predictions were then made of the effect of low CRRT dose on the change in serum phosphate levels after implementation of CRRT. The model predicted that CRRT at a low dose using phosphate-free RRT solutions will limit, but not eliminate, the incidence of hypophosphatemia. Further, the model predicted that CRRT at a low dose will have virtually no influence on the incidence of hyperphosphatemia when using phosphate-containing RRT solutions.

Conclusions: This report identifies the clinical measurements for using the proposed model for individualizing the CRRT dose and RRT phosphate concentration to maintain serum phosphate concentrations in a desired range.

引言：低磷血症在连续性肾脏替代治疗（continuous renal replacement therapy, CRRT）过程中较为常见，但通过静脉磷酸盐补充或在肾脏替代治疗（renal replacement therapy, RRT）溶液中添加磷酸盐，有望在治疗期间维持患者的血清磷酸盐水平。
方法：本研究构建了稳态磷酸盐质量平衡模型，旨在评估在使用无磷酸盐及含磷酸盐的RRT溶液时，CRRT剂量对血清磷酸盐浓度的影响，研究重点聚焦于低剂量CRRT场景。
结果：模型预测，通过采集CRRT启动前（初始）及治疗过程中（终末）的血清磷酸盐浓度检测值，结合CRRT剂量、治疗时长与磷酸盐补充情况的临床数据，可确定模型患者的相关参数，即CRRT启动前磷酸盐的初始生成速率与清除率。随后，研究人员基于既往多项公开研究中报道的标准剂量或高剂量CRRT对应的患者平均数据，计算得到模型参数。基于典型患者的代表性模型参数，本研究进一步预测了低剂量CRRT对治疗后血清磷酸盐水平变化的影响。模型预测，采用无磷酸盐RRT溶液的低剂量CRRT，可在一定程度上降低低磷血症的发生率，但无法完全消除该病症。此外，模型还预测，若使用含磷酸盐的RRT溶液，低剂量CRRT几乎不会对高磷血症的发生产生影响。
结论：本研究明确了应用所提出模型的临床检测指标，可通过个体化调整CRRT剂量与RRT溶液的磷酸盐浓度，将患者血清磷酸盐水平维持在目标范围内。