Nomenclature for renal replacement therapy and blood purification techniques in critically ill patients: practical applications

The use of renal replacement therapy (RRT) in the management of acute kidney injury (AKI) requires a multidisciplinary approach. It is, therefore, essential that all members of the team use the same terminology, but the terms used to describe the different modalities of RRT often vary and can be confusing. In this article, we provide an updated consensus nomenclature to help navigate this complex field. We review the practical applications of transmembrane solute and fluid transport principles and the control mechanisms for RRT devices. The article focuses on continuous renal replacement therapies (CRRTs), which are commonly used in the treatment of critically ill patients. We hope that this standardized terminology will be adopted by all involved in this field, including industry as they develop new devices.

A conference was organized in Vicenza, Italy, to gather experts in CRRT and members of companies manufacturing CRRT hardware and devices to establish consensus on technical terminology and definitions relevant to basic principles of CRRT and related technologies [1]. The conference provided the background for a modified Delphi consensus methodology as previously utilized for the Acute Disease Quality initiative consensus sessions [2]. Prior to the conference, participants screened the literature of the last 25 years and previous taxonomy efforts [3‐5]. Keywords included “continuous renal replacement therapy”, “dialysis”, “hemofiltration”, “convection”, “diffusion”, “ultrafiltration”, “dose”, “blood purification”, “renal support”, “multiorgan dysfunction”, together with the relative MeSH (Medical Subject Headings) terms. Abstracts of 707 articles were screened and more than 300 papers were read in full and analyzed. Based on this literature search, a series of definitions and terms were proposed and consensus was achieved from the majority of experts who participated in the conference. Where consensus was lacking, different statements were created after two-thirds of the audience expressed a positive vote. We present the results of this effort of terminology harmonization called the Nomenclature Standardization Initiative (NSI).

CRRT “hardware” includes the machine and all dedicated disposables. Knowledge of the nomenclature and the functions of the machine and its main components is extremely important, not only for nurses and technicians but also for clinicians.

Figure 1 depicts a standard CRRT machine equipped with current technology and characteristics [6, 7]. Its main components include:

The different procedures performed by the machine [8] include:

Disposables (single-use components of the extracorporeal circuit) are specific for every machine and are usually designed for a specific treatment modality. The main disposables [9] and color codes that should mark each tubing line are listed in Table 1.

During CRRT, the filter is the key disposable through which blood or plasma is effectively purified by ultrafiltration, convection, and/or diffusion. Historically, the designation “filter” describes the entire purifying extracorporeal device system (i.e., membranes, housing, etc.). Among the different types of filters, hemofilters, hemodialyzers, and hemodiafilters should be used when exclusively convective, diffusive, or convective plus diffusive modalities, respectively, are applied. In this article we use these terms distinctly, taking into account the different CRRT modalities. A plasma filter is defined as a specific filter that allows the separation of plasma from cellular elements. Sorbents, cartridges, and adsorbers do not belong to the category of filters; in this case, adsorption is the only purifying modality. The only available type of CRRT filter that can perform diffusive and/or convective transport is shaped as a collection of parallel “hollow fibers”. The filters can be mainly identified by membrane geometrics and performance characteristics [10‐12].

Fluid management during CRRT must take into account the volume and hemodynamic status of the patient. The machine fluid balance error is the fluid management error caused by CRRT machine malfunction. Based on the inherent variability (“tolerances”) in the performance of the fluid pumps, scales, and other components of a CRRT machine’s fluid management system, the manufacturer provides a specified limit (“specification”) beyond which a fluid imbalance is considered an error. Fluid imbalances can be due to hardware (scales, pumps, tubes) or software (control system and protective subsystem) errors. Various systems have been proposed for fluid balancing in CRRT machines:

All these methods can be applied individually or in combination.

Extracorporeal therapies can be categorized according to session frequency and duration.

Application of technology at the bedside requires full knowledge of the basic principles and the operating mechanisms for every technique. When faced with a complex patient, practitioners can use a growing variety of extracorporeal treatment options. For patients with multiple organ failure, an increasingly rich panoply of options is being developed, including extracorporeal treatments for sepsis and for cardiac, pulmonary, and liver failure [40‐44]. In this complex scenario, a multidisciplinary clinical care team composed of specialists from different disciplines and highly trained nurses is crucial to the success of the treatment. We suggest a framework for harmonization of terminology to reduce the errors and complications that can result from poor understanding and inadequate delivery of the prescribed therapies. Homogenized nomenclature is also important when reporting machine functions and clinical parameters to enable study comparisons and advance our understanding in this field, ultimately allowing for improvements in clinical practice and patient outcomes.

We trust that new publications, electronic medical records, and machine software will be designed and operated in compliance with the agreed terminology to enable consistent data collection and comparison.