What is the initial evaluation and management of acute kidney injury?

Initial Evaluation and Management of Acute Kidney Injury

The initial evaluation of acute kidney injury (AKI) should include serum creatinine measurement, complete blood count, urinalysis with microscopy, urine chemistry, and renal ultrasonography to determine the cause as prerenal, intrinsic renal, or postrenal. 1

Definition and Diagnosis of AKI

AKI is defined by any of the following criteria according to KDIGO guidelines:

• Increase in serum creatinine by ≥0.3 mg/dL (≥26.5 μmol/L) within 48 hours, OR
• Increase in serum creatinine to ≥1.5 times baseline within the prior 7 days, OR
• Urine output <0.5 mL/kg/h for >6 hours 2, 1

AKI Staging

Stage	Serum Creatinine	Urine Output
1	1.5-1.9× baseline OR ≥0.3 mg/dL increase	<0.5 mL/kg/h for 6-12h
2	2.0-2.9× baseline	<0.5 mL/kg/h for ≥12h
3	≥3.0× baseline OR ≥4.0 mg/dL OR initiation of RRT	<0.3 mL/kg/h for ≥24h OR anuria for ≥12h

Initial Diagnostic Evaluation

1. Laboratory workup:

   • Serum creatinine and BUN
   • Complete blood count with differential
   • Serum electrolytes with calculated anion gap
   • Urinalysis with microscopy
   • Urine chemistry including sodium and creatinine (for calculating fractional excretion of sodium) 1, 3

2. Imaging:

   • Renal ultrasonography should be performed in most patients, particularly older men, to rule out obstruction 4, 3

3. Determine AKI etiology:

   • Prerenal: Volume depletion, hypotension, decreased cardiac output
   • Intrinsic renal: Acute tubular necrosis, glomerulonephritis, interstitial nephritis
   • Postrenal: Urinary tract obstruction 4, 3

Management Algorithm

Step 1: Immediate Interventions

• Discontinue all nephrotoxic medications (NSAIDs, aminoglycosides, contrast agents) 2, 1
• Assess and optimize volume status:
  • For hypovolemia: Administer isotonic crystalloids (preferred over colloids) 1
  • For volume overload: Consider diuretics (only for volume management, not to treat AKI itself) 1

Step 2: Specific Management Based on AKI Stage

For Stage 1 AKI:

• Daily monitoring of serum creatinine and electrolytes
• Strict intake and output monitoring
• Daily weight measurements 1

For Stage 2-3 AKI:

• All measures for Stage 1
• Consider volume expansion with albumin (1g/kg) for 48 hours 1
• Consider nephrology consultation 3

Step 3: Management of Complications

• Hyperkalemia: Treat if potassium >5.5 mEq/L with insulin/glucose, sodium bicarbonate, calcium gluconate, and potassium binders
• Metabolic acidosis: Consider sodium bicarbonate if pH <7.2
• Volume overload: Diuretics for management, not as treatment for AKI itself 1

Step 4: Consider Renal Replacement Therapy (RRT) for:

• Refractory hyperkalemia
• Volume overload unresponsive to diuretics
• Severe metabolic acidosis
• Uremic symptoms (encephalopathy, pericarditis, pleuritis)
• Certain toxin ingestions 1

Special Considerations

• Pre-existing CKD: More frequent creatinine monitoring (every 12-24 hours) and lower threshold for nephrology consultation 1
• Cirrhosis: Close monitoring, removing risk factors, reducing/withdrawing diuretics, treating infections, and plasma volume expansion for hypovolemia 1

Follow-up After AKI

• Evaluate kidney function 3 months after an AKI episode to screen for development of chronic kidney disease
• Monitor for resolution, new onset, or worsening of pre-existing kidney disease
• Adjust medications as kidney function recovers 1, 5

Common Pitfalls to Avoid

• Failure to identify and discontinue nephrotoxic medications
• Inappropriate use of diuretics to "treat" AKI rather than manage volume overload
• Inadequate volume resuscitation in hypovolemic patients
• Delayed nephrology consultation for severe or complex cases
• Lack of follow-up after AKI resolution, which can lead to missed diagnosis of CKD 3, 5

AKI is associated with increased mortality, risk of cardiovascular events, and progression to chronic kidney disease. Early recognition, prompt management, and appropriate follow-up are essential to improve outcomes and prevent long-term complications.