Slow continuous ultrafiltration and prolonged intermittent renal replacement therapy: Tailoring renal replacement therapy in intensive care unit

Acute kidney injury complicates the clinical course of nearly half of all critically ill patients admitted to intensive care, conferring a three-to five-fold elevation in mortality risk. The management of these patients has evolved considerably beyond standardized protocols toward individualized therapeutic strategies. Within this paradigm shift, two modalities warrant particular attention: Slow continuous ultrafiltration (SCUF) and prolonged intermittent renal replacement therapy (PIRRT). SCUF operates through isolated fluid extraction at rates between 100 mL and 500 mL per hour, targeting patients whose preserved kidney function nonetheless fails to manage severe volume overload. The clinical experience with SCUF reveals a complex picture, while certain patient populations, particularly those receiving extracorporeal membrane oxygenation or battling refractory cardiac failure, have shown encouraging results with shortened intensive care stays, equally robust cohorts have experienced concerning progression rates to complete renal replacement therapy and mortality approaching or exceeding 50%. The distinction appears to hinge on meticulous patient selection, with systolic perfusion pressure emerging as a pivotal hemodynamic threshold. PIRRT extends conventional intermittent therapy from the traditional 3-4 hours window to sessions lasting 6-12 hours. Multiple investigations support that this approach achieves comparable mortality and renal recovery outcomes to continuous modalities while reducing costs, facilitating patient mobilization, and decreasing nursing requirements. Current guideline recommendations increasingly favor restrictive, patient-centered approaches over rigid algorithmic initiation. Accumulating evidence supports ultrafiltration rates of 1-1.5 mL/kg/hour, adjusted dynamically according to hemodynamic tolerance and disease trajectory. Yet despite these refinements in our understanding of optimal therapy delivery, fundamental questions persist: Which patients derive maximal benefit from alternative modalities? When should these therapies be initiated or withdrawn, and how can we predict individual treatment response? This review synthesizes current evidence to establish practical decision frameworks for implementing SCUF and PIRRT in critically ill populations, examining clinical indications, safety parameters, fluid removal strategies, and outcome determinants. Our objective is to advance renal replacement therapy from a standardized intervention toward precision nephrology for high-acuity patients.