Renal replacement therapy in ICU: from conservative to restrictive strategy

Renal replacement therapy (RRT) is a cornerstone of the management of severe acute kidney injury (AKI) in critically ill patients. Despite being life-saving in several instances, RRT may be associated with significant complications, including bleeding, hemodynamic instability, infections, thrombosis, and possibly delayed renal recovery. Large randomized controlled trials (RCTs) have demonstrated that delaying RRT initiation, in the absence of life-threatening complications (conservative RRT strategy) allows 38% to 49% of patients to avoid RRT. In addition to reducing unnecessary treatment, this conservative approach may help protect kidney function [1,2,3]. Once RRT is initiated, intensivists usually prescribe a recommended (or standard) dose of RRT (a KT/V of 3.9 per week when using intermittent hemodialysis or extended RRT; an effluent volume of 20–25 ml/kg/h for continuous RRT) [4]. This ensures the efficacy of metabolic control but there remains significant uncertainty about how long RRT should be continued. In daily clinical practice, empirical criteria (i.e. increased urine output or decreased blood urea nitrogen) are used to guide RRT weaning. Current guidelines offer indeed little guidance on how to manage this process.

Given the safety of a conservative RRT initiation strategy, we suggest extending this concept to a new approach (called restrictive RRT strategy) that could potentially solve the hot topic questions of RRT dosing and RRT weaning. This approach would consist in the suspension of RRT after 3 days. At this moment, metabolic abnormalities that mandated RRT initiation would no longer be present and the cause of AKI would be, in most cases, treated (for instance by controlling sepsis or hemorrhage). Then the question would be the same as before the initiation of the first RRT session i.e., does the situation require starting RRT or can it be delayed until a conservative RRT initiation criterion is observed again? If RRT is resumed, the patient will receive a new RRT session, after which RRT will again be suspended. This targeted approach applied until renal recovery-would ensure the use of RRT only when truly necessary rather than its prolongation for vague reasons. The restrictive strategy differs from ongoing studies that investigate the intensity of each RRT session (only for continuous RRT modality) (NCT06446739, NCT06014801, NCT06021288). Indeed, a restrictive approach would not diminish the intensity of each session, well the contrary, but the number of sessions by suspending pending a new indication for resumption occurs. Although this approach presents methodological challenges, we believe it is essential to evaluate it regardless of the initial RRT modality—intermittent (IHD) or continuous (CRRT)—since neither has shown definitive superiority.

The potential benefits of a restrictive RRT strategy for patients are numerous. By reducing unnecessary RRT exposure, patients could experience fewer episodes of hemodynamic instability, a common complication during RRT sessions, and a lower risk of infections, particularly those related to RRT catheters. Additionally, minimizing RRT may promote faster renal recovery by avoiding the "second hit" that RRT can impose on the kidneys [1, 5]. Fewer RRT sessions would make general patient management such as physiotherapy or transport easier. Patients might also experience better sleep quality, as RRT machines and alarms are a frequent source of disturbances improving the overall ICU environment. Moreover, RRT is a resource-intensive procedure, and minimizing its use would reduce both costs and the carbon footprint of critical care, in an era of increasing attention to healthcare sustainability [6].

On the other hand, shortening RRT sessions often raises concerns about achieving an adequate dose. Yet more intensive therapy does not necessarily translate into better outcomes in the ICU. Large RCTs have shown no mortality advantage for high-dose RRT regimens [7, 8], and recent meta-analyses even suggest that higher-intensity therapy may delay renal recovery [9]. Notably, the three above mentioned ongoing trials of low-dose CRRT demonstrate that the concept of a lower-dose intervention is considered sufficiently acceptable to be rigorously tested—thus challenging the assumption that less intensive dialysis automatically means unsafe underdialysis. However, these trials still focus on fixed-dose CRRT rather than a truly individualized approach and do not aim at reducing the number of sessions nor determining the moment for cessation. By contrast, by centering on individual patient needs, the restrictive strategy we propose aligns more closely with the ultimate goal of personalized medicine—an essential objective in modern critical care.

As we reconsider how to best use RRT, a more selective, needs-based approach could be the key to optimizing care. We are currently applying for a grant from the French Ministry of Health to conduct an RCT to evaluate this restrictive RRT strategy, focusing on a tailored approach providing no more than what is warranted.