*3.1.2 Predicting the need of RRT*

As shown in those studies where a substantial number of patients randomized to a delayed strategy never required RRT initiation, correctly predicting who will progress to an AKI stage where RRT is required is complex in a real-life setting. Since the last decade, a growing number of tools and biomarkers have been developed, and reported useful, to inform about the likelihood a patient with AKI will worsen, and progress to receive RRT [16]. Various urine and blood biomarkers have been studied, such as the urine neutrophil gelatinase-associated lipocalin (uNGAL), interleukin-18 (IL18), or the NephroCheck (TIMP2\*IGFBP7), with a pooled AUC or 0.720, 0.668 and 0.857 respectively. More functional biomarkers, such as a diuretic response of less than 200 mL to a loading dose of 1.0 to 1.5 mg/kg of intravenous furosemide (FST – Furosemide stress test) have also been shown useful in predicting the risk of progression to RRT with a pooled sensitivity and specificity of respectively 0.84 (95% CI 0.72–0.91) and 0.77 (95% CI 0.64–0.87) [17]. The growing interest in such complementary tools is associated with the publication of multiple confirmation studies in recent years, leading to recent consensus in favor of their use in standard clinical practice [18]. However, their implementations in real-life ICU settings are still in the beginning.

## *3.1.3 Conclusion*

In summary, only the first smallest single-center RCT of almost entirely surgical patients has shown a mortality benefit of early initiation of RRT compared to a delayed strategy. The three subsequent trials consisting of more than four thousand patients with a variety of modalities and populations (including surgical subgroup analysis) concluded the absence of such advantages of early initiation. Also, the added resources required to initiate 35–45% more RRT must not be neglected. Furthermore, significant harms have been reported in the early-initiation approach: catheter-related bloodstream infections (AKIKI), 90-day RRT dependence, and any adverse event (STARRT-AKI). On the other hand, the latest trial might help in determining the upper limit of postponing RRT. Therefore, a conservative approach consisting of watchful waiting, unless a life-threatening indication emerges, seems recommended for most cases with the caveats that the risk-benefits ratio is uncertain once criteria used for inclusion in the latest trial are reached.
