Acute Kidney Injury According to KDIGO
Acute kidney injury is defined by KDIGO as an increase in serum creatinine ≥0.3 mg/dL (≥26 μmol/L) within 48 hours, OR an increase in serum creatinine to ≥1.5 times baseline within 7 days, OR urine output <0.5 mL/kg/hour for 6 hours. 1
KDIGO Staging Criteria
AKI severity is classified into three stages based on the degree of creatinine elevation or urine output reduction 1:
Stage 1: Creatinine rise ≥0.3 mg/dL (≥26 μmol/L) within 48 hours OR 1.5-1.9 times baseline within 7 days OR urine output <0.5 mL/kg/hour for 6-12 hours 1
Stage 2: Creatinine 2.0-2.9 times baseline within 7 days OR urine output <0.5 mL/kg/hour for ≥12 hours 1
Stage 3: Creatinine ≥3.0 times baseline OR creatinine ≥4.0 mg/dL (≥354 μmol/L) with acute rise ≥0.3 mg/dL OR urine output <0.3 mL/kg/hour for ≥24 hours OR anuria for ≥12 hours OR initiation of renal replacement therapy 1
Initial Management Approach
Immediate Actions
The cornerstone of AKI management is hemodynamic optimization with isotonic crystalloid resuscitation for hypovolemic patients and immediate discontinuation of all nephrotoxic medications. 1, 2, 3
Discontinue these medications immediately 2, 4, 5:
- NSAIDs (including over-the-counter medications)
- ACE inhibitors and ARBs
- Diuretics (in volume-depleted patients)
- Aminoglycosides and other nephrotoxic antibiotics
- Avoid the "triple whammy" combination of NSAIDs + diuretics + ACE inhibitors/ARBs, which more than doubles AKI risk 4, 5
Fluid Management Strategy
Use isotonic crystalloids (not colloids) for initial volume expansion in patients with or at risk for AKI. 1, 3 This recommendation is based on lack of benefit from colloids and evidence that hydroxyethyl starches increase AKI incidence and mortality 1, 3. Balanced crystalloid solutions are preferred over normal saline 5.
Critical caveat: Avoid overly aggressive fluid administration in non-hypovolemic patients, as this worsens outcomes and can lead to fluid overload 2, 4. Assess volume status through clinical examination including jugular venous pressure, peripheral edema, lung auscultation, orthostatic vital signs, and daily weights 2, 4, 5.
Diagnostic Workup
Obtain kidney ultrasound immediately to rule out obstructive uropathy 2, and perform urinalysis with microscopy to detect hematuria, proteinuria, or abnormal sediment that may indicate intrinsic renal disease 2, 5, 6.
Categorize AKI as prerenal (volume depletion, heart failure), intrinsic renal (acute tubular necrosis, glomerulonephritis), or postrenal (obstruction) to guide treatment 5, 6.
Monitoring Requirements
Monitor serum creatinine and electrolytes every 4-6 hours initially for severe AKI (Stage 2-3), or every 2-4 days for Stage 1 AKI 2, 5. Track strict fluid balance with input/output measurements 2, 4.
Indications for Renal Replacement Therapy
Urgent RRT is indicated for 2:
- Severe oliguria unresponsive to fluid resuscitation
- Refractory hyperkalemia
- Severe metabolic acidosis
- Volume overload causing pulmonary edema
- Uremic complications (encephalopathy, pericarditis, bleeding)
- Certain toxin removal
Continuous RRT is preferred in hemodynamically unstable patients 3, 7. Reassess the need for continued RRT daily 2, 4.
Medications to Avoid
Do NOT use these agents for AKI treatment, as they lack efficacy and may cause harm 1:
- Dopamine for renal protection
- Loop diuretics to treat oliguria (though may be used for volume management)
- N-acetylcysteine for AKI prevention
- Recombinant human IGF-1
Nephrology Referral Criteria
Urgent nephrology consultation is required for 5, 8:
- Stage 2 or 3 AKI
- Unclear etiology despite initial workup
- Suspected glomerulonephritis or vasculitis
- No improvement with initial treatment within 48-72 hours
- Need for RRT
Post-AKI Follow-up
All patients who experience AKI should have clinical follow-up within 3 months to assess for resolution, new-onset CKD, or worsening of pre-existing CKD 1, 5. This is particularly critical for patients with Stage 3 AKI requiring temporary RRT or those with persistent renal dysfunction at discharge 1.
Common Pitfalls to Avoid
- Continuing nephrotoxic medications during AKI causes ongoing kidney damage 2, 4
- Delaying RRT when clear indications exist increases mortality 2, 4
- Failing to adjust medication dosages as kidney function changes dynamically during AKI leads to toxicity or underdosing 2, 4, 9
- Overly rapid correction of severe hyponatremia can cause osmotic demyelination syndrome 2
- Inappropriate continuation of ACE inhibitors/ARBs in volume depletion or sepsis worsens AKI 5
Patient Education
Educate patients to avoid over-the-counter NSAIDs, maintain adequate hydration, recognize symptoms requiring immediate medical attention (decreased urine output, swelling, shortness of breath), and inform all healthcare providers about their prior AKI episode 4, 5.