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（hypophosphatemia）在连续性肾脏替代治疗（continuous renal replacement therapy, CRRT）中较为常见，但可通过静脉补磷或在肾脏替代治疗（renal replacement therapy, RRT）溶液中添加磷酸盐，在治疗过程中维持血清磷水平。
方法：本研究构建了磷酸盐稳态质量平衡模型，以评估使用无磷及含磷RRT溶液时，CRRT剂量对血清磷浓度的影响，重点关注低剂量CRRT场景。
结果：模型预测，通过采集CRRT前（初始）及CRRT中（终末）的血清磷浓度检测值，结合CRRT剂量、治疗时长及补磷情况的临床数据，可确定模型患者参数，即CRRT前的初始磷酸盐生成速率与清除率。随后，本研究基于既往多篇文献中报道的标准剂量或高剂量CRRT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实施后对血清磷水平变化的影响。模型预测，采用无磷RRT溶液的低剂量CRRT，可限制但无法完全消除低磷血症的发生。此外，模型预测，若使用含磷RRT溶液，低剂量CRRT几乎不会对高磷血症（hyperphosphatemia）的发生率产生影响。
结论：本研究明确了应用所提出模型所需的临床检测指标，以实现CRRT剂量与RRT溶液磷浓度的个体化调整，从而将血清磷浓度维持在目标范围内。