Acute Kidney Injury & Failure (AKI): A Guide to Diagnosis and Management | Definition, Etiologies, Classification, Symptoms, Causes, General Approach & Treatments

Definition

KDIGO Criteria

• increase in serum creatinine by 0.3mg/dL within 48 hours or
• > 1.5x fold increase in serum creatinine from baseline within 7 days or
• Urine output < 0.5 ml/kg/hr for at least 6 hours (least validated criteria)

Etiologies

Two Most Common Causes:

• Prerenal
• Acute Tubular Necrosis

both are 65 - 75% the cause

Classification

AKI in three categories:

• Prerenal
• Intrinsic
• Postrenal

Prerenal
Due to true volume loss or decreased effective arterial blood volume

• Hypovolemia: GI losses, Dehydration, diuretics, hemorrhage, 3rd spacing, burns
• Drugs: ACEI/ARB, NSAIDs
• Decreased effective arterial supply: cardiorenal, hepatorenal, sepsis

Intrinsic
Due to damage to the glomeruli, tubules, or interstitium
Causes: 

• GN (glomerulonephritis)
• AIN (acute interstitial nephritis) 
• ATN (Acute tubular necrosis)

                  - Toxic (contrast dye, heme pigment, some abx)
                  - Ischemic

Postrenal 
Due to damage/obstruction along the urinary tract system
Causes:

• Tumor 
• Kidney stone 
• Trauma to the urinary tract
• Cellular debri 
• Prostate enlargement 

General Approach

History

• Signs of infection
• IV contrast exposure
• Vomiting or diarrhea 
• P.O. intake
• Recent procedures Medications (including NSAIDs and antibiotics) 
• History/features of CHF/cirrhosis 
• Urinary symptom history 

Physical Exam

• Pulse - tachycardia
• Blood pressure - hypotension
• Signs of dehydration
• Orthostatics
• Signs of fluid overload

Labs

• Urinalysis
• Basic Metabolic Panel
• If appearing hypovolemic, can give fluid trial

Second Tier Tests:

• Fractional excretion of sodium (FeNa) or 
• Fractional excretion of Urea (FeUrea) if on diuretics

FeNa= Na(urine) X Cr(serum)/ Na(serum) X Cr(urine)

• Urine sodium 
• Urine/serum osmolality 
• Urine protein/creatinine 
• Urine eosinophils 
• Imaging (renal US, CT abdomen) 
• Post-void residual (can consider with the initial phase of workup)

Third Tier Testing:

• Serologic testing 
• Complement levels (C3, C4)
• Serum and urine protein electrophoresis/ (SPEP/UPEP)
• Renal biopsy

Treatment

• P.O. or IV fluids (if prerenal)
• Avoid nephrotoxic meds
• Close kidney function monitoring (follow strict I/O's + creatinine)
• Correct abnormal electrolytes/acid-base 

Indications for Urgent Dialysis (A,E,I,O,U)

• Acid-base disturbance 
• Electrolyte disturbance (K+) 
• Intoxications
• Overload of Volume
• Uremia

3 TAKE HOME POINTS

• Get a good history: dehydration, infection, known CHF or cirrhosis, recent meds (including OTCs)
• Majority of AKI is secondary to prerenal or ATN etiology
• If the patient does no appear volume up, start with a fluid trial

Take a good history and consider fluids