What are the causes and symptoms of Acute Kidney Injury (AKI)?

From the Guidelines

Acute kidney injury (AKI) should be managed by identifying and addressing the underlying cause, with a focus on stopping nephrotoxic medications, ensuring adequate hydration, and monitoring fluid balance carefully, as evidenced by the most recent study 1.

Key Considerations

• AKI is diagnosed by a 50% or greater sustained increase in serum creatinine over a short period of time, which is also reflected as a rapid decrease in eGFR 1.
• People with diabetes are at higher risk of AKI than those without diabetes, and other risk factors include preexisting CKD, the use of medications that cause kidney injury, and the use of medications that alter renal blood flow and intrarenal hemodynamics 1.
• Elevations in serum creatinine (up to 30% from baseline) with renin-angiotensin system (RAS) blockers must not be confused with AKI, and ACE inhibitors and ARBs should not be discontinued for minor increases in serum creatinine (<30%) in the absence of volume depletion 1.

Management Strategies

• Initial management includes stopping nephrotoxic medications, ensuring adequate hydration while avoiding volume overload, and monitoring fluid balance carefully.
• For prerenal AKI, intravenous fluids like normal saline at 10-20 mL/kg over 1-2 hours may be appropriate, followed by reassessment.
• Electrolyte abnormalities, particularly hyperkalemia (potassium >5.5 mEq/L), require urgent treatment with calcium gluconate 10% (10 mL IV over 2-3 minutes), insulin (10 units regular insulin with 50 mL of 50% dextrose IV), and sodium bicarbonate (50 mEq IV) if acidotic.
• Severe AKI may necessitate renal replacement therapy, particularly with refractory hyperkalemia, severe acidosis (pH <7.2), volume overload unresponsive to diuretics, or uremic symptoms.

Monitoring and Outcomes

• Daily monitoring of kidney function, electrolytes, and urine output is essential, with urine output goals of at least 0.5 mL/kg/hour.
• AKI is serious because it can lead to permanent kidney damage, chronic kidney disease, or death if not properly managed, making early intervention critical 1.

From the Research

Definition and Diagnosis of Acute Kidney Injury

• Acute kidney injury (AKI) is defined as an increase in serum creatinine or a decrease in urine output over hours to days 2.
• The severity of AKI is classified according to urine output and elevations in creatinine level 3.
• AKI can be diagnosed using standard criteria based on changes in serum creatinine, urine output, or both 4.

Causes and Risk Factors of Acute Kidney Injury

• The etiologies of AKI are categorized as prerenal, intrinsic renal, and postrenal 2, 3.
• Accurate diagnosis of the underlying cause is key to successful management and includes a focused history and physical examination, serum and urine electrolyte measurements, and renal ultrasonography when risk factors for a postrenal cause are present 3.
• Patients with AKI are at increased risk of mortality, cardiovascular events, and progression to chronic kidney disease 2, 3.

Management and Treatment of Acute Kidney Injury

• Initial evaluation and management of AKI in the community setting includes laboratory work-up, medication adjustment, identification and reversal of underlying cause, and referral to appropriate specialty care 2.
• General management principles for AKI include determination of volume status, fluid resuscitation with isotonic crystalloid, treatment of volume overload with diuretics, discontinuation of nephrotoxic medications, and adjustment of prescribed drugs according to renal function 3.
• Nephrology consultation should be considered when there is inadequate response to supportive treatment and for AKI without a clear cause, stage 3 or higher AKI, preexisting stage 4 or higher chronic kidney disease, renal replacement therapy, and other situations requiring subspecialist expertise 3.

Biomarkers and Outcomes of Acute Kidney Injury

• Novel biomarkers for renal tissue damage, such as NGAL or cystatin C, may become altered well before creatinine or oliguria signal a condition of reduced kidney function 5.
• Oliguria is an important sign of kidney dysfunction and can be used to diagnose and assess the severity of AKI 5, 6.
• The consideration of urine output criteria enables identification of AKI in patients who may not have been diagnosed using serum creatinine criteria alone, and is associated with higher 90-day mortality 6.