Approach to Acute Kidney Injury
The management of acute kidney injury (AKI) requires prompt identification of the underlying cause, implementation of supportive measures, and prevention of further kidney damage through a systematic approach that includes fluid management, medication review, and consideration of renal replacement therapy when indicated. 1
Definition and Diagnosis
AKI is defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria:
| Stage | Serum Creatinine Criterion | Urine Output Criterion |
|---|---|---|
| 1 | Increase ≥0.3 mg/dL within 48h or 1.5-1.9 times baseline | <0.5 mL/kg/h for 6-12h |
| 2 | 2.0-2.9 times baseline | <0.5 mL/kg/h for ≥12h |
| 3 | ≥3.0 times baseline or ≥4.0 mg/dL or RRT initiation | <0.3 mL/kg/h for ≥24h or anuria for ≥12h |
Initial Diagnostic Evaluation
Categorize the etiology:
- Prerenal (reduced kidney perfusion)
- Intrinsic renal (direct kidney damage)
- Postrenal (urinary tract obstruction)
Key diagnostic tests:
- Serum creatinine and BUN
- Complete blood count
- Urinalysis and urine sediment examination
- Fractional excretion of sodium (FENa)
- Renal ultrasound (especially in older men to rule out obstruction) 2
Management Approach
1. Initial Management
- Reassess the underlying etiology of AKI when it persists beyond 48 hours 1
- Precise measurement of kidney function (timed urine creatinine clearance is currently the best available estimate) 1
- Monitor for complications including fluid overload, acidosis, and hyperkalemia 1
2. Fluid Management
- Ensure adequate hydration and volume status - this is essential in preventing and treating AKI 1
- Use isotonic crystalloids rather than colloids for initial volume expansion 3
- Initial bolus of 500-1000 mL for hypovolemic patients, then reassess 3
- Target neutral to negative fluid balance after initial resuscitation 3
- Avoid rapid fluid removal (>1.5-2 L/day) to prevent hemodynamic instability 3
3. Medication Management
- Discontinue nephrotoxic medications:
- NSAIDs
- Aminoglycosides
- Contrast agents 3
- Temporarily hold:
- ACE inhibitors/ARBs
- Diuretics
- Beta-blockers in appropriate cases 3
- Adjust medication dosages according to renal function 2
4. Monitoring and Supportive Care
Daily monitoring:
- Serum creatinine, BUN, electrolytes
- Fluid balance and daily weights
- Hemodynamic parameters
- Acid-base status 3
Nutritional support:
- 20-30 kcal/kg/day total energy intake
- 0.8-1.0 g/kg/day protein for non-catabolic AKI patients without dialysis
- 1.0-1.5 g/kg/day for patients on renal replacement therapy 3
5. Renal Replacement Therapy (RRT)
Consider RRT when the following are present:
- Severe metabolic acidosis
- Refractory hyperkalemia
- Volume overload unresponsive to diuretics
- Uremic symptoms 3
Modality selection:
- Continuous renal replacement therapy (CRRT) for hemodynamically unstable patients
- Intermittent hemodialysis (IHD) for stable patients 3
Special Considerations
Persistent AKI
When AKI persists:
- Re-evaluate possible causes of AKI
- Consider additional tests (urine sediment, proteinuria, biomarkers, imaging)
- Consider nephrology consultation 1
Risk Factors for AKI
Identify patients with risk factors:
- Dehydration or volume depletion
- Advanced age
- Female gender
- Black race
- Chronic kidney disease
- Chronic diseases (heart, lung, liver)
- Diabetes mellitus
- Cancer
- Anemia 3
Follow-up and Long-term Management
- Schedule follow-up within 3 months to assess for development of chronic kidney disease 3
- More frequent monitoring for high-risk patients 3
- Long-term follow-up is essential as even one episode of AKI increases the risk of cardiovascular disease, chronic kidney disease, and death 4
When to Consult Nephrology
Consider nephrology consultation for:
- Inadequate response to supportive treatment
- AKI without a clear cause
- Stage 3 or higher AKI
- Preexisting stage 4 or higher chronic kidney disease
- Need for renal replacement therapy 2
The traditional approach of classifying AKI as pre-renal, renal, and post-renal is being reconsidered, as terms like "pre-renal" can be misinterpreted as "hypovolemic" and may encourage indiscriminate fluid administration. A more beneficial framework may be to distinguish between conditions that reduce glomerular function, conditions that result in injury of tubules and/or glomeruli, and conditions that do both 1.