Failure

Acute Kidney Injury

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Acute Kidney Injury, Acute Renal Failure, Acute Renal Insufficiency, Renal Failure, Azotemia, Uremia, Acute Tubular Necrosis, Acute Intrinsic Renal Failure

  • Epidemiology
  1. Incidence of Acute Kidney Injury
    1. Overall: 2-3 per 1000 persons
    2. Hospital: 7% of patients
    3. ICU: Two thirds of patients
  • Definitions
  1. Acute Kidney Injury
    1. Abrupt onset (within 48 hours) and
    2. Reduced Renal Function (Serum Creatinine elevation) and/or
    3. Urine Output decreased and/or
    4. Renal replacement therapy (Dialysis)
  2. Uremia
    1. Blood homeostasis defects related to Renal Failure
    2. Includes Fluid Overload, Hyperkalemia and Metabolic Acidosis
  3. Azotemia
    1. Accumulation of nitrogen waste products in the blood (Blood Urea Nitrogen)
  • Causes
  1. See Acute Renal Failure Causes
  2. Prerenal Failure (shock)
    1. See Acute Prerenal Failure
    2. See Prerenal Failure Causes
    3. See Medication Causes of Prerenal Failure
    4. Shock states
      1. Hypovolemic shock (e.g. Hemorrhagic Shock, dehydration)
      2. Cardiogenic Shock (CHF)
      3. Septic Shock
      4. Anaphylactic shock
  3. Intrinsic Renal Failure
    1. See Intrinsic Renal Failure Causes
    2. Vascular Injury (e.g. Renal Artery Stenosis, Aortic Dissection or Abdominal Aortic Aneurysm)
    3. Glomerulonephritis (e.g. SLE, PSGN)
    4. Malignant Hypertension
    5. Interstitial (analogous to an Allergic Reaction within the Kidney)
      1. See Acute Interstitial Nephritis
      2. See Medication Causes of Interstitial Nephritis
    6. Tubular (most common intrinsic cause)
      1. Final common pathway of Kidney injury resulting in cell death and necrosis (analogous to ARDS)
      2. See Acute Tubular Necrosis (20-30% of Acute Kidney Injury Causes)
      3. See Medication Causes of Acute Tubular Necrosis
  4. Postrenal Failure (obstruction)
    1. See Acute Postrenal Failure
    2. See Postrenal Failure Causes
    3. See Medication Causes of Postrenal Failure
    4. Benign Prostatic Hyperplasia (BPH)
    5. Urethral stricture
    6. Nephrolithiasis
  • Symptoms
  • Severe Kidney Injury
  1. Fatigue
  2. Anorexia
  3. Nausea or Vomiting
  4. Weight gain
  5. Edema
  6. Confusion (uremic encephalopathy)
  • Signs
  • Clinical Clues to Kidney injury cause
  1. Cardiovascular exam
    1. Lower extremity edema
      1. Congestive Heart Failure
      2. Nephrotic Syndrome
    2. Skin turgur
      1. Tenting in dehydration
  2. Abdominal exam
    1. Abdominal Aortic Aneurysm
      1. Pulsatile mass
      2. Abdominal bruit
    2. Abdominal Distention
      1. Ascites
    3. Pelvic mass
    4. Prostate enlargement
    5. Distended Bladder
  3. Skin
    1. Rash of drug-induced Interstitial Nephritis
    2. Palpable Purpura
      1. Vasculitis
    3. Non-palpable Purpura
      1. Thrombotic Thrombocytopenic Purpura (TTP)
      2. Hemolytic Uremic Syndrome (HUS)
    4. Livido reticularis
    5. Spider angioma or caput medusae (Cirrhosis)
  • Stages
  1. Stage 1
    1. Serum Creatinine increased >1.5-2x baseline (or >0.3 mg/dl increase) or
    2. Urine Output <0.5 ml/kg/hour for >6 hours
  2. Stage 2
    1. Serum Creatinine increased >2-3x baseline or
    2. Urine Output <0.5 ml/kg/hour for >12 hours
  3. Stage 3
    1. Serum Creatinine increased >3x baseline or
    2. Serum Creatinine >4.0 mg/dl and acute increase of at least 0.5 mg/dl
    3. Urine Output <0.3 ml/kg/hour for >24 hours (or Anuria for 12 hours)
    4. Requires renal replacement therapy (Dialysis)
  • Labs
  1. Renal Function: Criteria for Acute Renal Failure
    1. See Stages above
    2. Serum Creatinine rises >0.3 mg/dl on 2 contiguous days or
    3. Serum Creatinine rises >0.5 mg/dl or
    4. Serum Creatinine rises >1.5 fold above baseline or
    5. Calculated GFR falls >50% below baseline
  2. Serum electrolytes
    1. Serum Potassium (Hyperkalemia)
    2. Serum Sodium
    3. Serum bicarbonate (Metabolic Acidosis)
    4. Serum Calcium
    5. Serum Phosphorus
    6. Serum Magnesium
  3. Fractional Excretion of Sodium (FENa)
    1. Requires urine sample prior to IV fluids and Diuretics
    2. FENa >2%: Intrinsic renal disease (e.g. Acute Tubular Necrosis)
      1. Falsely elevated FENa if on Diuretics
      2. Consider Fractional Excretion of Urea (FEUrea) if on Diuretics
      3. An injured Kidney loses the ability to concentrate urine
    3. FENa <1%: Prerenal Failure
      1. Kidney still able to concentrate urine
      2. Not specific for prerenal causes (see FeNa)
  4. Fractional Excretion of Urea (FEUrea)
  5. Complete Blood Count (CBC)
    1. Acute Hemolytic Anemia
      1. Obtain Serum Bilirubin fractionated, serum LDH, Haptoglobin and Peripheral Smear (see below)
      2. May suggest Hemolytic Uremic Syndrome or Thrombotic Thrombocytopenic Purpura
    2. Platelets decreased in uremic Platelet Dysfunction
      1. May be accompanied with bleeding, Purpura
    3. Eosinophils increased in interstitial disease
  6. Autoimmune Testing for Glomerular Disease (Glomerulonephritis)
    1. Antinuclear Antibody (ANA)
    2. Antiglomerular basement membrane Antibody
    3. Antineutrophil Cytoplasmic Antibody (ANCA)
      1. See Small Vessel Vasculitis
    4. Antistreptolysin O
      1. Poststreptococcal Glomerulonephritis
    5. Complement Level
      1. Low in some causes of Acute Glomerulonephritis
  7. Percutaneous Renal Biopsy
    1. Indicated for Glomerular or Interstitial disease
    2. May be urgent in certain cases with rapid progression, Oliguria or positive urine sediment
      1. Consult with Nephrology early when intrinsic Acute Kidney Injury is considered
      2. Glucocorticoids and other immunosuppressants as well as plasmophoresis may be indicated based on biopsy
  1. Most important single test in identifying Acute Kidney Injury cause
  2. Urine Specific Gravity
    1. Prerenal Failure: Specific Gravity >1.020
    2. Intrarenal Failure: Specific Gravity 1.010 - 1.020
  3. Vascular disease
    1. Urine RBCs often present
  4. Glomerulonephritis, Vasculitis or Multiple Myeloma
    1. Urine RBCs and red cell casts
    2. Granular Casts
    3. Proteinuria (esp. >3 grams)
  5. Interstitial Nephritis (includes drug hypersensitivity)
    1. Pyuria
    2. Eosinophils
    3. White Blood Cell Casts and Eosinophil casts
  6. Tubular Necrosis
    1. Pigmented Granular Casts
    2. Renal tubular epithelial cells
    3. Granular Casts
  7. Prerenal Failure
    1. Hyaline Casts
  8. Rhabdomyolysis
    1. Orthotolidine positive on Urine Dipstick with negative microscopy for Red Blood Cells
  • Labs
  • Additional to consider if indicated
  1. Serum Protein Electrophoresis (SPEP) and Urine Protein electrophoresis (UPEP)
    1. Multiple Myeloma
  2. Uric Acid
    1. Postrenal Failure
  3. Serum Creatine Phosphokinase (CPK) and serum myoglobin
    1. Rhabdomyolysis
  4. Blood Cultures
    1. Endocarditis
  5. HIV Test
    1. HIV Nephropathy
  6. Metabolic Acidosis with increased Anion Gap and increased Osmolar Gap
    1. Acute ingestion (Ethylene gylcol, Methanol)
  7. Peripheral Smear for Hemolysis
    1. Autoimmune Vasculitis (e.g. TTP, HUS, SLE)
  1. See Inferior Vena Cava Ultrasound for Volume Status
  2. See Echocardiogram in Congestive Heart Failure (and Echocardiogram)
  3. See Abdominal Aorta Ultrasound
  4. See Bladder Ultrasound
    1. Evaluate for post-void residual urine >100 ml (Bladder scan, Ultrasound or catheter)
  5. See Renal Ultrasound
    1. Obtain formal diagnostic renal Ultrasound in most patients
    2. Intrarenal Failure: May show parenchymal abnormality
    3. Postrenal Failure: Hydronephrosis
  • Evaluation
  1. Step 1: Confirm Acute Kidney Injury criteria
    1. See Creatinine under labs above (as well as stages)
    2. Distinguish from Chronic Kidney Disease with normal fluctuation
  2. Step 2: Assess Urine Output
    1. No Oliguria
      1. Go to step 3
    2. Oliguria
      1. Acute Prerenal Failure
        1. Fractional Excretion of Sodium (FENa) <1%
        2. Distinguish volume overload (e.g. CHF) from Dehydration
      2. Acute Intrinsic Renal Failure or Postrenal Failure
        1. Fractional Excretion of Sodium (FENa) <1%
        2. Go to step 3
  3. Step 3: Renal Ultrasound
    1. Hydronephrosis
      1. Postrenal Failure
    2. Small Kidneys bilaterally
      1. Acute on Chronic Renal Failure
    3. Kidneys of normal size
      1. Go to step 4
  4. Step 4: Urinalysis
    1. Interpret urine sediment for cause of renal parenchymal condition (see Urinalysis above)
  5. Step 5: Additional evaluation
    1. See specific labs as above