Division of Nephrology, Hypertension and Renal Transplantation, University of Florida, Gainesville, FL, USA.
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, USA.
Clin Kidney J. 2012 Jun;5(3):212-6. doi: 10.1093/ckj/sfs045. Epub 2012 Apr 20.
Slow continuous ultrafiltration (SCUF) is a safe and efficient treatment for fluid overload in patients who are hemodynamically unstable, have low urine output, and are not in need of dialysis or hemofiltration for solute clearance. Sustained anticoagulation is required for these long treatments, thus posing clinically challenges for patients having contraindications to systemic anticoagulation with heparin. Regional citrate anticoagulation would be an alternative option; however, we believed that this would be problematic due to citrate kinetics that predicted the development of metabolic alkalosis.
In that patients' serum bicarbonate reached 45 mEq/L and arterial pH rose to 7.59 after just 3 days of SCUF, we developed equations to study this phenomenon. We report here the acid-base balance calculations quantifying base accumulation in SCUF compared to continuous venovenous hemofiltration (CVVH).
This kinetic approach demonstrates the importance of accounting for the high citrate clearance into CVVH hemofiltrate, which prevents development of the alkalosis seen with the relatively low ultrafiltration rates in SCUF: there was net bicarbonate accumulation of ∼1400 mmol/day with SCUF, compared to 664 to as low as 274 mmol/day during CVVH. The calculations underscore the importance of the relative fluid flow rates as well as the bicarbonate and citrate levels in the various infused solutions. We also discuss how citrate's acid-base effects are potentially complicated by metabolism via gluconeogenic and ketone body pathways.
These acid-base balance findings emphasize why clinicians must be mindful of the risk of metabolic alkalosis when using continuous renal replacement therapy modalities with low rates of ultrafiltration, which thereby presents a contraindication for using citrate anticoagulation for SCUF.
在血流动力学不稳定、尿量少且不需要透析或血液滤过清除溶质的患者中，缓慢持续超滤（SCUF）是一种安全有效的治疗方法，可用于治疗液体超负荷。这些长时间的治疗需要持续抗凝，因此对于存在肝素全身抗凝禁忌证的患者，这在临床上是一个挑战。局部枸橼酸抗凝可能是一种替代选择；然而，我们认为这会有问题，因为枸橼酸盐动力学预测代谢性碱中毒的发生。
在仅仅 3 天的 SCUF 后，患者血清碳酸氢盐达到 45mEq/L，动脉 pH 值上升至 7.59，我们据此制定了研究该现象的方程。在此，我们报告酸碱平衡计算结果，该结果量化了 SCUF 与连续静脉-静脉血液滤过（CVVH）相比的超滤量对碱中毒的影响。
这种动力学方法表明，在 CVVH 血液滤过中，必须考虑到大量枸橼酸盐清除的重要性，这可以防止 SCUF 中相对较低的超滤率引起的碱中毒：与 CVVH 相比，SCUF 时有大约 1400mmol/天的净碳酸氢盐积累，而在 CVVH 中，这一数值低至 664mmol/天，甚至低至 274mmol/天。这些计算结果强调了相对流体流速以及各种输注溶液中碳酸氢盐和枸橼酸盐水平的重要性。我们还讨论了枸橼酸盐的酸碱作用如何因糖异生和酮体途径的代谢而变得复杂。
这些酸碱平衡研究结果强调了为什么临床医生在使用超滤率低的连续性肾脏替代治疗模式时必须注意代谢性碱中毒的风险，这也是 SCUF 中使用枸橼酸抗凝的禁忌证。
