Methods for dose quantification in continuous renal replacement therapy: Toward a more precise approach

Abstract

Periodic dose assessment is quintessential for dynamic dose adjustment and quality control of continuous renal replacement therapy (CRRT) in critically ill patients with acute kidney injury (AKI). The flows-based methods to estimate dose are easy and reproducible methods to quantify (estimate) CRRT dose at the bedside. In particular, quantification of effluent flow and, mainly, the current dose (adjusted for dialysate, replacement, blood flows, and net ultrafiltration) is routinely used in clinical practice. Unfortunately, these methods are critically influenced by several external unpredictable factors; the estimated dose often overestimates the real biological delivered dose quantified through the measurement of urea clearance (the current effective delivered dose). Although the current effective delivered dose is undoubtedly more precise than the flows-based dose estimation in quantifying CRRT efficacy, some limitations are reported for the urea-based measurement of dose. This article aims to describe the standard of practice for dose quantification in critically ill patients with AKI undergoing CRRT in the intensive care unit. Pitfalls of current methods will be underlined, along with solutions potentially applicable to obtain more precise results in terms of (a) adequate marker solutes that should be used in accordance with the clinical scenario, (b) correct sampling procedures depending on the chosen indicator of transmembrane removal, (c) formulas for calculations, and (d) quality controls and benchmark indicators.

Keywords: clearance; dialysance; nomenclature; sieving coefficient; urea.

FIGURE 1

Advantages and drawbacks of flows‐based dose estimation and solutes‐based dose measurement. Flows‐based methods to estimate dose are certainly easier and feasible to apply at the bedside. Among solutes‐based methods to measure dose, the identification of marker solutes that could be easily measured in real time, at a low cost, at the bedside could provide a feasible alternative to the standard urea‐based approach. Measurement of the current effective delivered dose certainly quantifies biologic (real) clearance more accurately than the flows‐based estimation methods. Furthermore, in accordance with the clinical scenario and the specific patient’s needs, specific and more “precise” solutes might be chosen for measuring the current effective delivered dose (eg, those solutes whose clearance was the main objective of the extracorporeal treatment). However, the flows‐based methods provide an estimation of dose which is independent from the clinical scenario (eg, from the occurrence of membrane fouling or vascular access recirculation) and from the specific indications for continuous renal replacement therapy (CRRT) (eg, hypermyoglobinemia)