Acute kidney injury

Background

• Majority of cases of community-acquired ARF is secondary to volume depletion

RIFLE Classification

• Risk - Serum Cr increased 1.5x baseline
• Injury - Serum Cr increased 2.0x baseline
• Failure - Serum Cr increased 3.0x baseline OR Cr >4 and acute increase >0.5
• Loss - Complete loss of kidney function for >4wk
• ESRD - Need for renal replacement therapy for >3mo

Chronic Kidney Disease Stages

• Useful if pt's baseline creatinine is unknown
  • Stage 1: Kidney damage (e.g. proteinuria) and normal GFR; GFR >90
  • Stage 2: Kidney damage (e.g. proteinuria) and mild decr in GFR; GFR 60-89
  • Stage 3: Moderate decrease in GFR; GFR >30-59
  • Stage 4: Severe decrease in GFR; GFR 15-29
  • Stage 5: Kidney failure (dialysis or kidney transplant needed); GFR <15

Risk Factors

• Radiocontrast agents
  • Esp if GFR <60, hypovolemic
• Atherosclerosis
• Chronic hypertension
• Chronic kidney disease
• NSAIDs
• ACEI/ARB
• Sepsis
• Hypercalcemia
• Hepatorenal syndrome

Etiology

Prerenal

• Hypovolemia
  • GI: decreased intake, vomiting and diarrhea
  • Pharmacologic: diuretics
  • Third spacing
    • Pancreatitis
  • Skin losses: fever, burns
  • Miscellaneous
    • Hypoaldosteronism
    • Salt-losing nephropathy
    • Postobstructive diuresis
• Hypotension
  • Septic vasodilation
  • Hemorrhage
  • Decreased cardiac output
    • Ischemia/infarction
    • Valvulopathy
  • Pharmacologic
    • B-blockers
    • CCBs
    • Antihypertensive medications
  • High-output failure
    • Thyrotoxicosis
    • AV fistula
• Renal artery and small-vessel disease
  • Embolism: thrombotic, septic, cholesterol
  • Thrombosis: atherosclerosis, vasculitis, sickle cell disease
  • Dissection
  • Pharmacologic
    • NSAIDs
    • ACEI/ARB
      • Observed shortly after initiation of therapy
  • Microvascular thrombosis
    • Preeclampsia
    • HUS
    • DIC
    • vasculitis
    • SCD
  • Hypercalcemia

Intrinsic

• Tubular diseases
  • Ischemic acute tubular necrosis
    • Caused by more advanced disease due to the prerenal causes
• Nephrotoxins
  • Aminoglycosides, radiocontrast, amphotericin, heme pigments ([[rhabdo, hemolysis)
  • Obstruction
    • Uric acid, calcium oxalate, myeloma, amyloid
    • Pharmacologic: sulfonamide, triamterene, acyclovir, indinavir
• Interstitial diseases
  • Acute interstitial nephritis: typically a drug reaction (NSAIDs, abx, phenytoin)
  • Infection: bilateral pyelonephritis, Legionnaire disease, hantavirus
  • Infiltrative disease: sarcoidosis, lymphoma
  • Autoimmune diseases: SLE
• Glomerular diseases
  • Rapidly progressive glomerulonephritis
    • Goodpasture, Wegener granulomatosis, HSP, SLE, membranoproliferative GN
  • Postinfectious glomerulonephritis
• Small-vessel diseases
  • Microvascular thrombosis
    • Preeclampsia, HUS, DIC, TTP, vasculitis (PAN, SCD, atheroembolism)
  • Malignant hypertension
  • Scleroderma
  • Renal vein thrombosis

Postrenal

• Infants and children
  • Urethra and bladder outlet
    • Anatomic malformations
      • Urethral atresia
      • Meatal stenosis
      • Anterior and posterior urethral valves
  • Ureter
    • Anatomic malformations
      • Vesicoureteral reflux (female preponderance)
      • Ureterovesical junction obstruction
      • Ureterocele
      • Retroperitoneal tumor
• All ages
  • Various locations in GU tract
    • Trauma
    • Blood clot
  • Urethra and bladder outlet
    • Phimosis or urethral stricture (male preponderance)
    • Neurogenic bladder
      • DM, spinal cord disease, multiple sclerosis, Parkinson's
      • Pharmacologic: anticholinergics, a-adrenergic antagonists, opiates
• Adults
  • Urethra and bladder outlet
    • BPH
    • Cancer of prostate, bladder, cervix, or colon
    • Obstructed catheters
  • Ureter
    • Calculi, uric acid crystals
    • Papillary necrosis
      • SCD, DM, pyelonephritis
    • Tumor: Ureter, uterus, prostate, bladder, colon, rectum; retroperitoneal lymphoma
    • Retroperitoneal fibrosis: idiopathic, tuberculosis, sarcoidosis, propranolol
    • Stricture: TB, radiation, schistosomiasis, NSAIDs
    • Miscellaneous
      • Aortic aneurysm
      • Pregnant uterus
      • IBD
      • Trauma

Clinical Features

• Acute renal failure itself has few symptoms until severe uremia develops:
  • N/V, drowsiness, fatigue, confusion, coma
• Pts more likely to present w/ symptoms related to underlying cause:
  • Prerenal
    • Thirst, orthostatic light-headedness, decreasing urine output
  • Intrinsic
    • Flank pain, hematuria
      • Nephrolithiasis
      • Papillary necrosis
      • Crystal-induced nephropathy
    • Myalgias, seizures, recreational intoxication
      • Pigment-induced ARF (rhabdo)
    • Darkening urine and edema (esp w/ preceding pharyngitis or cutaneous infection)
      • Acute glomerulonephritis
    • Fever, arthralgia, rash
      • Acute interstitial nephritis
    • Cough, dyspnea, hemoptysis
      • Goodpasture, Wegener granulomatosis
  • Postrenal
    • Alternating oliguria and polyuria is pathognomonic of obstruction
    • Anuria

Diagnosis

• Prerenal
  • BUN/Cr ratio > 20
  • FeNa <1% ((urine sodium/plasma sodium) / (urine creatinine / serum creatinine))
    • < 2% for neonates
  • Urine osm >500
  • Urine sodium < 20 mEq/L
  • Specific gravity > 1.020
  • Fractional excretion of urea < 35%
  • Microscopic analysis
    • Hyaline casts
• Instrinsic
  • FeNa >1%
    • > 2.5% for neonates
  • Urine Osm <350
  • Urine sodium > 40 mEq/L
  • Specific gravity < 1.020
  • Fractional excretion of urea > 50%
  • Microscopic analysis
    • Acute glomerulonephritis: RBCs, casts
    • Acute tubular necrosis: protein, tubular epithelial cells
• Postrenal
  • FeNa >1%
  • Urine Osm <350

Work-up

• Urine
• Prostate exam
• UA, urine sodium, urine creatinine, urine urea
• ECG (hyperkalemia)

Imaging

• CXR
• Evidence of volume overload, PNA
• US
  • Test of choice in setting of acute renal failure
  • Bladder size (post-void)
  • Hydronephrosis
  • IVC collapsibility (prerenal)
• CT
  • Useful to determine cause of post renal failure (identification of abdominal masses etc.)
  • Should generally not be used with IV contrast due to potential risk for CIN
  • Indicated if hydronephrois found on US in order to define the location of obstruction

Treatment

• Treat underlying cause
• IVF (prerenal)
• Obstruction
  • Note: Postobstructive diuresis can result in significant volume loss and death
    • Typically occurs when obstruction has been prolonged / has resulted in renal failure
    • Admit pts w/ persistent diuresis of >250 mL/h for >2hr
  • Foley Catheter, consider Coude Catheter
  • Suprapubic (if Coude fails)
• Dialysis
  • Indicated for:
    • A: Acidosis (severe)
    • E: Electrolyte abnormality (e.g. uncontrolled hyperkalemia)
    • I: Ingestions (lithium, ASA, methanol, ethylene glycol, theophylline)
    • O: Overload (volume) w/ persistent hypoxia
    • U: Uremic pericarditis/encephalopathy/bleeding dyscrasia
    • Also:
      • Na <115 or >165 mEq/L
      • BUN >100

Disposition

Admit

See Also

• Hyperkalemia
• Ultrasound: Renal
• Hypertensive emergency

Source

Tintinalli