Acute Kidney Injury Classification and Management
Introduction to AKI
- AKI is classified into three categories based on anatomic location: prerenal, intrarenal, and postrenal, with prerenal and intrarenal causes accounting for over 97% of cases 1
Prerenal AKI Causes
- Hypovolemia, decreased cardiac output, systemic vasodilation, renal vasoconstriction, and renal artery occlusion are common causes of prerenal AKI 2
Intrarenal AKI Causes
- No cited facts are available for intrarenal AKI causes
Postrenal AKI Causes
- Ureteral obstruction, bladder outlet obstruction, and urethral obstruction are causes of postrenal AKI 2
AKI Definition and Diagnosis
- AKI is defined by KDIGO criteria as an increase in serum creatinine ≥0.3 mg/dL within 48 hours, or an increase to ≥1.5 times baseline within 7 days, or urine output <0.5 mL/kg/hr for 6 consecutive hours 1, 3, 2
AKI Staging
| Stage | Serum Creatinine Criteria | Urine Output Criteria |
|---|---|---|
| Stage 1 | 1.5-1.9× baseline OR ≥0.3 mg/dL increase | <0.5 mL/kg/hr for 6-12 hours |
| Stage 2 | 2.0-2.9× baseline | <0.5 mL/kg/hr for ≥12 hours |
| Stage 3 | ≥3.0× baseline OR ≥4.0 mg/dL (with acute rise >0.3 mg/dL) OR initiation of RRT | <0.3 mL/kg/hr for ≥24 hours OR anuria for ≥12 hours |
Progression and Mortality
- Progression through AKI stages strongly correlates with increased mortality 2
- Even small increases in creatinine (≥0.3 mg/dL) independently associate with approximately four-fold increased hospital mortality 2
BUN-Creatinine Ratio
- The BUN-Creatinine Ratio helps differentiate prerenal from intrarenal AKI: a ratio >20:1 suggests prerenal azotemia, while a ratio <15:1 suggests intrarenal disease 2
Inadequate Urine Output
- Oliguria is defined as urine output <0.5 mL/kg/hr for 6 hours, and anuria as <100 mL/24 hours or complete absence of urine for 12 hours 1, 3, 2
Emergency Hemodialysis Indications
- The mnemonic "AEIOU" captures absolute indications for emergency dialysis, including acidosis, electrolytes, intoxications, overload, and uremia 2
Hyperkalemia Management
- Immediate treatment priorities for hyperkalemia include cardiac membrane stabilization, intracellular potassium shift, and potassium removal from the body 2
ECG Changes in Hyperkalemia
- ECG changes in hyperkalemia include peaked T waves, prolonged PR interval, flattened/absent P waves, widened QRS complex, and sine wave pattern 2
Hyponatremia Classification
- Hyponatremia is classified by volume status and serum osmolality, including hypotonic, isotonic, and hypertonic hyponatremia 2
CKD Staging
| Stage | Description | eGFR (mL/min/1.73m²) | Clinical Features |
|---|---|---|---|
| 1 | Kidney damage with normal GFR | ≥90 | Albuminuria, hematuria, structural abnormalities |
| 2 | Mild reduction in GFR | 60-89 | Usually asymptomatic |
| 3a | Mild-moderate reduction | 45-59 | Increased cardiovascular risk |
| 3b | Moderate-severe reduction | 30-44 | Anemia, bone disease may develop |
| 4 | Severe reduction | 15-29 | Prepare for renal replacement therapy |
| 5 | Kidney failure | <15 or dialysis | Uremic symptoms, requires RRT |
Nephrotic Syndrome
- The classic tetrad of nephrotic syndrome includes heavy proteinuria, hypoalbuminemia, edema, and hyperlipidemia 1
- Nephrotic-range proteinuria is defined as ≥3.5 g protein per 24 hours or urine protein-to-creatinine ratio ≥3.5 g/g (or ≥350 mg/mmol) 1
Edema Pathophysiology
- Edema formation is governed by Starling forces across capillary membranes, including capillary hydrostatic pressure, interstitial hydrostatic pressure, reflection coefficient, capillary oncotic pressure, and interstitial oncotic pressure 2