Extreme Fluid Accumulation Syndrome or Compartmental Balance Disorder? A Sepsis-Associated Acute Kidney Injury Case Report and Literature Review

<b>Background:</b> Fluid accumulation syndrome (FAS) is a well-recognized predictor of adverse outcomes in critically ill patients, particularly in the context of sepsis and cardiorenal syndrome. However, extreme cases of fluid accumulation exceeding 60 L are rare and poorly described. We report a unique case of severe, multifactorial congestion and discuss the diagnostic and therapeutic challenges, including the role of bedside ultrasound and venous congestion assessment, as well as the importance of bioelectric impedance analysis (BIA) for patient monitoring and follow-up. <b>Case Presentation:</b> We describe the clinical course of a 51-year-old male with dilated cardiomyopathy and infectious endocarditis who underwent tricuspid valve surgery complicated by cardiogenic and septic shock. The patient developed progressive congestion despite maximal medical management. Serial BIA and venous excess ultrasound (VExUS) assessments were used to monitor venous congestion and guide renal replacement therapy (RRT). A targeted literature review was performed to contextualize this case within current evidence on FAS and Compartment Balance Disorder in Intensive Care Units (CBD-ICUs). <b>Results:</b> The patient accumulated over 68 L of positive fluid balance due to prolonged vasopressor support, multiorgan failure, nutritional and infectious complications. Continuous and then intermittent hemodiafiltration, guided by point-of-care ultrasound and BIA, allowed gradual decongestion. Renal function recovered, and ventilator support was weaned after 120 days in intensive care. The literature review highlighted the prognostic relevance of FAS and emerging tools such as BIA and VExUS for individualized fluid management. <b>Conclusions:</b> Extreme FAS may reflect a failure of systemic and compartmental fluid regulation in critically ill patients (CBD-ICU). VExUS-guided decongestion, BIA and early RRT may improve outcomes in complex scenarios of overlapping cardiorenal and septic syndromes.