What is hepatorenal syndrome (HRS)?

What is Hepatorenal Syndrome?

Hepatorenal syndrome (HRS) is a functional form of acute kidney injury that occurs in patients with decompensated cirrhosis and ascites, characterized by renal vasoconstriction and impaired kidney function without significant structural kidney damage, driven by severe circulatory dysfunction from portal hypertension. 1, 2

Core Definition and Classification

HRS represents a primarily functional renal failure unique to patients with advanced liver disease, where the kidneys themselves are structurally intact but fail due to profound hemodynamic alterations. 3, 4 The condition has been reclassified into two distinct forms:

• HRS-AKI (formerly Type 1 HRS): Characterized by rapid, progressive renal impairment with serum creatinine increasing ≥100% to >2.5 mg/dL in less than 2 weeks, representing the acute and more severe form. 1

• HRS-CKD (formerly Type 2 HRS): Features stable or slowly progressive renal impairment with a more chronic course. 1

Pathophysiological Mechanisms

The development of HRS follows a complex cascade of hemodynamic and inflammatory events:

Primary Hemodynamic Dysfunction

• Splanchnic arterial vasodilation is the initiating event, causing reduction in effective arterial blood volume despite total plasma volume expansion—creating a paradoxical state where the body perceives volume depletion. 1, 5

• Portal hypertension from cirrhosis leads to increased sinusoidal hydrostatic pressure, driving lymph formation and contributing directly to ascites development. 1

• This arterial underfilling triggers compensatory activation of the sympathetic nervous system and renin-angiotensin-aldosterone system (RAAS), leading to renal vasoconstriction and progressive decline in glomerular filtration rate. 1, 5

Circulatory Dysfunction

• Cirrhotic cardiomyopathy impairs the heart's ability to increase cardiac output sufficiently to compensate for peripheral vasodilation, worsening the hyperdynamic circulatory state. 1

• The combination of decreased mean arterial pressure and activated vasoconstrictor systems causes sodium and water retention, followed by decreased renal blood flow. 1

Inflammatory and Molecular Mechanisms

• Bacterial translocation from increased gut permeability (due to portal hypertension) contributes to systemic inflammation, with bacterial products and cytokines worsening splanchnic and systemic vasodilation. 1

• Inflammatory signals affect proximal tubular cells, leading to mitochondria-mediated metabolic downregulation and cellular dysfunction. 1

• Increased synthesis of vasoactive substances (cysteinyl leukotrienes, thromboxane A2, endothelin-1) further impairs renal blood flow and glomerular microcirculation. 1

Diagnostic Criteria

The American Association for the Study of Liver Diseases requires the following for HRS diagnosis:

• Cirrhosis with ascites 1
• Serum creatinine >1.5 mg/dL 1
• No improvement after 2 consecutive days of diuretic withdrawal and albumin expansion (1 g/kg) 1
• Absence of shock 1
• No nephrotoxic drug exposure 1
• Exclusion of structural kidney disease (no proteinuria >500 mg/day, no microhematuria >50 RBCs/high-power field, normal renal ultrasound) 1

A critical pitfall: The old criteria requiring creatinine ≥2.5 mg/dL have been revised—do not delay treatment waiting for this threshold, as earlier intervention improves outcomes. 1

Clinical Significance and Prognosis

• HRS-AKI is the third most common cause of AKI in cirrhotic patients after prerenal azotemia and acute tubular necrosis. 6

• Bacterial infections, particularly spontaneous bacterial peritonitis, are the most important precipitating factors for HRS development. 1

• Median survival of untreated Type 1 HRS is approximately 1 month, with mortality rates approaching 90% at three months without treatment. 1, 6

• Despite being classified as "functional" renal failure, severe and/or repeated episodes of renal hypoperfusion can lead to structural kidney damage over time, exposing kidneys to direct hemodynamic injury. 1

Structural Considerations

While HRS is primarily functional, prolonged or repeated episodes of severe renal hypoperfusion can result in actual structural kidney damage, blurring the line between purely functional and organic renal failure. 1 This underscores the importance of early recognition and aggressive treatment to prevent irreversible kidney injury.