What are the causes of pre-renal Acute Kidney Injury (AKI)?

From the Guidelines

Pre-renal acute kidney injury (AKI) is primarily caused by conditions that reduce blood flow to the kidneys, such as hypotension, hypovolemia, decreased cardiac output, or renal artery occlusion, as stated in the 2021 study published in the Journal of the American College of Radiology 1. Pre-renal AKI is often multifactorial but generally includes impaired blood flow from any cause. The most common causes include:

• Volume depletion from dehydration, hemorrhage, excessive vomiting, diarrhea, or diuretic use
• Decreased cardiac output conditions such as heart failure, cardiogenic shock, or severe arrhythmias
• Systemic vasodilation from sepsis, anaphylaxis, or certain medications that can cause hypotension and subsequent kidney hypoperfusion
• Medications that affect kidney blood flow, particularly NSAIDs, ACE inhibitors, and ARBs
• Renal artery stenosis or occlusion directly reduces blood supply to the kidneys
• Hepatorenal syndrome in advanced liver disease and abdominal compartment syndrome with increased intra-abdominal pressure can also compromise renal perfusion. According to the study, AKI is common, affecting up to 20% of hospital inpatients and between 30% to 60% of critically ill patients 1, and pre-renal factors are a significant contributor to this condition. Pre-renal AKI is typically reversible if the underlying cause is promptly identified and corrected, with treatment focusing on restoring adequate kidney perfusion through fluid resuscitation, discontinuation of offending medications, or management of the primary condition affecting cardiac output or vascular tone. Evaluation of the patient with AKI includes a thorough history, physical examination, and laboratory analysis of blood and urine, as well as identification of the specific cause of AKI, which is critical for appropriate intervention 1.

From the Research

Causes of Pre-Renal AKI

• Pre-renal AKI is caused by decreased renal perfusion, which can be due to low intravascular volume or decreased arterial pressure 2
• Approximately 70% of community-acquired cases of acute kidney injury are attributed to pre-renal causes 2
• Autoregulatory mechanisms can partially compensate renal perfusion reduction in order to maintain glomerular filtration rate (GFR), but these mechanisms are impaired in patients with pre-existing chronic kidney disease 2
• Pre-renal AKI can be caused by kidney hypoperfusion, which can lead to a low urine flow rate and low urine sodium initially 3
• Other causes of pre-renal AKI include abdominal compartment syndrome and urinary tract obstruction, which can also lead to a low urine flow rate and low urine sodium initially 3

Pathophysiology of Pre-Renal AKI

• The pathophysiology of pre-renal AKI involves a reduction in renal perfusion, which can lead to a decrease in GFR 2
• The reduction in renal perfusion can be due to various factors, including low intravascular volume, decreased arterial pressure, and increased venous pressure 3
• The decrease in GFR can lead to a buildup of waste products in the blood, which can cause further damage to the kidneys 4

Diagnosis of Pre-Renal AKI

• The diagnosis of pre-renal AKI can be made using anamnestic and biochemical criteria, including the fractional excretion of sodium, the urinary-to-plasma creatinine ratio, and the renal failure index 5
• A composite biochemical criterion based on the congruency of at least two of the three biochemical ratios can be used to classify patients as pre-renal or intrinsic AKI 5
• Urinary injury biomarkers, such as NGAL and KIM-1, can also be used to diagnose pre-renal AKI and distinguish it from intrinsic AKI 5