Supplementary Material for: Sampling from extracorporeal circuit: a step forward for dose monitoring in CRRT

Introduction: Continuous renal replacement therapies (CRRT) require constant monitoring and periodic treatment readjustments, being applied to highly complex patients, with rapidly changing clinical needs. To promote precision medicine in the field of renal replacement therapy and encourage dynamic prescription, the Acute Dialysis Quality Initiative (ADQI) recommends periodically measuring the solutes extracorporeal clearance with the aim of assessing the current treatment delivery and the gap from the therapeutic prescription (often intended as effluent dose). To perform this procedure, it is therefore necessary to obtain blood and effluent samples from the extracorporeal circuit to measure the concentrations of a target solute (usually represented by urea) prefilter, post-filter and in the effluent line. However, samples must be collected simultaneously from the extracorporeal circuit ports, with the same suction flow at unknown rate. Methods: The proposed study takes the first steps toward identifying the technical factors that should be considered in determining the optimal suction rate to collect samples from the extracorporeal circuit to measure the extracorporeal clearance for a specific solute. Results: The results obtained identify the low suction rate (i.e., 1 ml/min) as an ideal parameter for an adequate sampling method. Low velocities do not perturb the external circulation system and ensure stable prevailing pressures in the circuit. Higher velocities can be allowed only with blood flows above 120 ml/min preferably in conditions of appropriate filtration fraction. Discussion/Conclusions: The specific value of aspiration flow rate must be proportioned to the prescription of CRRT treatments set by the clinician.

引言：连续性肾脏替代治疗（CRRT）需持续监测并周期性调整治疗方案，其适用人群为临床需求快速变化的极危重症患者。为推动肾脏替代治疗领域的精准医学实践、促进动态化治疗处方制定，急性透析质量倡议（ADQI）建议定期检测溶质体外清除率，以此评估当前治疗实施情况与治疗处方（通常以流出液剂量为参照标准）之间的差距。完成该检测流程需从体外循环管路采集血液与流出液样本，以测定目标溶质（通常为尿素）在滤器前、滤器后及流出液管路中的浓度。但该操作要求同时从体外循环管路的各个采样接口采集样本，且各接口的抽吸流量需保持一致，而该流量初始为未知值。
方法：本研究率先明确了在确定最佳抽吸流量以采集体外循环管路样本、测定特定溶质体外清除率时，应予以考量的各类技术因素。
结果：本研究所得结果显示，低抽吸流量（即1 ml/min）可作为满足采样要求的理想参数。低速抽吸不会干扰体外循环系统，且可确保管路内压力维持稳定。仅当血流速度高于120 ml/min，且具备适宜滤过分数的条件下，方可采用更高的抽吸流量。
讨论与结论：抽吸流量的具体数值需与临床医师设定的CRRT治疗处方相匹配。