Correspondence regarding the article by Murugan et al. on “Precision net ultrafiltration dosing in continuous kidney replacement therapy: a practical approach”

To the Editor,

We read the article on precision net ultrafiltration by Murugan et al. [1] with concern. In this article, in addition to the misplaced use of the term continuous kidney replacement therapy instead of continuous renal replacement therapy (CRRT) [2], the main author subverts the very definition of net ultrafiltration (NUF), which he had previously espoused, advocated, and published [3, 4]. Moreover, he destabilises the accepted consensus nomenclature published by the Acute Disease Quality Initiative, which is that NUF is the difference between the effluent removed by the CRRT machine through the process of ultrafiltration and the dialysate and replacement fluid administered via the machine.

In contradiction to their previously determined description and against consensus nomenclature [5], the authors confuse the NUF with the fluid balance (the balance between what is removed by the machine (NUF) and all other fluid losses minus fluid inputs). The article then proceeds (Box 1) to describe an evidence-free process where unnecessary adjustments are made based on incomplete fluid balance. Adjustments that do not take into consideration the complex nature of fluid balance in critically ill patients, such as urinary output (which would occur in polyuric acute kidney injury (AKI), drains (as may be common and substantial after cardiac surgery or abdominal surgery), gastrointestinal losses (as may occur and be substantial in a proportion of critically ill patients), or nutritional input (as a major component of fluid input) are simply wrong.

We acknowledge that people can be free to call a platypus a duck. However, to do so causes unnecessary confusion and impedes the process of reproducible, clear, and consistent clinical research and terminology. As such it needs to be called out as both incorrect and undesirable. We invite the authors to join the rest of the world and adopt the accepted terminology in the future.