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Acute Kidney Injury. Also known as Acute Renal Failure. What is it?. Abrupt decrease in renal function Occurring over hours to days Results in retention of nitrogenous waste Elevated BUN/ Creatinine Current Criteria: Increase in serum creatinine of 0.5mg/dl

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acute kidney injury

Acute Kidney Injury

Also known as Acute Renal Failure

what is it
What is it?
  • Abrupt decrease in renal function
  • Occurring over hours to days
  • Results in retention of nitrogenous waste
  • Elevated BUN/Creatinine
  • Current Criteria:
    • Increase in serum creatinine of 0.5mg/dl
    • 25% increase in serum creatinine
    • 25% decrease in GFR
epidemiology
Epidemiology
  • Varies
  • 1-2% of hospital admissions
  • 2-5% during hospitalization
  • Up to 20% of ICU patients
  • Slightly more women than men
  • 140 million+ patients per year in western countries
three main etiology categories
Three Main Etiology Categories
  • Prerenal
    • Fall in Glomerular Perfusion
      • Decreased extracellular fluid
        • Hemorrhage, burn, vomiting, diuretics
      • Decreased circulating volume
        • Heart failure, cirrhosis, sepsis
  • Intrinsic Renal
    • Wait for it…
  • Post-renal
    • Obstruction
      • Prostatic enlargement, abdominal/pelvic tumor
intrinsic renal etiologies
Intrinsic Renal Etiologies
  • Acute Tubular Necrosis-most common
    • Ischemia
      • Untreated Pre-renal azotemia
    • Sepsis
    • Nephrotoxins
      • Exogenous:
        • Antibiotics, CONTRAST, chemo, ACEi
      • Endogenous:
        • Proteins-myeloma
        • Pigments: hemoglobin, myoglobin
        • Tumor Lysis Syndrome
        • Crystals-oxalate or uric acid
intrinsic renal etiologies1
Intrinsic Renal Etiologies
  • Acute Interstitial Nephritis
    • Antibiotics, NSAIDs
  • Vasculitis
    • Wegeners, microscopic polyarteritis
    • Cryoglobulinemia
  • Glomerulonephritis
    • Post-infectious, Goodpasture Syndrome
  • Urinary Tract Infection/Pyelonephritis
  • Atheroemboli-esp after procedures like heart catheterization
symptoms
Symptoms
  • Often, if already hospitalized, labs come first
    • Elevated BUN/Creatinine, oliguria
  • “Uremic” Symptoms
    • Fatigue, loss of appetite
    • Weakness
    • Nausea/vomiting
    • Metallic taste in mouth
    • Itching
    • Confusion
    • Fluid retention and Hypertension
physical exam
Physical Exam
  • Often, nothing notable
  • Signs of fluid retention
  • “Uremic” Signs
    • Pericardial friction rub
    • Asterixis
    • Mental status changes (without other cause)
  • Oliguria/Anuria
  • Can see tachypnea due to acidosis
  • Livedoreticularis-atheroemboli
laboratory studies
Laboratory Studies
  • This is how you make the diagnosis
  • Elevated BUN and serum Creatinine
  • Other possible serum abnormalities
    • Hyperkalemia
    • Low Bicarbonate
laboratory studies cont
Laboratory Studies (cont.)
  • Urinalysis is IMPORTANT-can help with etiology
    • Finely granular casts/hyaline casts-Prerenal
    • Dirty Brown coarse, granular casts-ATN
    • Tubular epithelial cells-ATN
    • Protein, blood
    • RBC casts-Glomerulonephritis
    • WBC casts-pyelonephritis
      • Without bacteria? Think AIN
    • Oxalate or Uric Acid crystals
work up
Work up
  • History And Physical/Review Hospital stay
    • This can often be most helpful to determine cause
  • Then determine which of the 3 categories it is:
    • Urinalysis with sediment
    • Urine osmolality
    • BUN/Creatinine Ratio
    • Fractional Excretion of Sodium (FENa)
      • Fractional Excretion of Urea (FEurea)
    • Renal Ultrasound-if doesn’t look like prerenal or intrinsic cause
other causes of elevated bun
Other Causes of Elevated BUN
  • GI bleed
  • Catabolic State
  • High Protein Diet
  • Systemic Steroid Use
management
Management
  • Best to PREVENT it if possible.
  • Mostly Symptomatic and dependent on cause
  • Prerenal? Improve circulating volume
    • IV fluids, stop diuretics, treat sepsis, CHF, or liver disease
  • Avoid Nephrotoxins
    • Metformin, diuretics, ACEi, further contrast studies
  • Treat Complications
complications
Complications
  • Hyperkalemia
    • Check the ECG->measure of the sum of the effects of Hyperkalemia, Hypocalcemia, acidosis.
  • Fluid Overload
    • Strict I&Os judicious loop diuretic use
  • Uremia
  • Acidosis
  • Calcium/Phosphate Imbalance
emergent dialysis for
Emergent Dialysis for:
  • A: acidosis refractory to medical therapy
  • E: electrolyte abnormalities
    • namely hyperkalemia
  • I: intoxications-e.g Lithium, Ethylene Glycol
  • O: Overload (fluid)
  • U: Uremia-severely symptomatic or BUN<80
prevention
Prevention
  • Avoid Nephrotoxins
    • Especially in elderly, volume depletion, or CKD
  • Hydration before and after radiocontrast studies.
  • Allopurinol before treating large tumors to prevent tumor lysis syndrome.
prophylaxis strategies for contrast induced nephropathy
Prophylaxis Strategies for Contrast Induced Nephropathy
  • JAMA. 2006;295:2765-2779. Review article.
  • No RCT to address all possibilities.
  • Hydration: Do it. Unless there is contraindication.
    • Normal Saline vs. Bicarbonate
      • Why bicarbonate? Alkalinization of urine to prevent tubular damage.
      • Studies show slight improvement or at least no worse outcome with bicarbonate (compared to normal saline), so that is the current recommendation.
      • 3mL/kg (D5 + 150mEq bicarbonate) x 1 hr pre-procedure then 1mL/kg of same fluid x 6 hr post-procedure. This is difficult to get done here.
    • N-acetylcysteine: currently recommended
      • 1200mg BID x2 doses before procedure then 1200mg BID x2 doses post-procedure.
important notes
Important Notes
  • Most people who develop AKI while hospitalized will not die of renal disease.
  • Many/Most will recover enough renal function to not require dialysis after discharge.
    • This is true for those with normal renal function prior to this incident, not necessarily for those with underlying CKD.
  • Most common cause of mortality is INFECTION-keep HD lines and other wounds clean to avoid iatrogenic cause of the infection.
references
References:
  • Sabatine, M. Nephrology section of Pocket Medicine.
  • Shaver, M.J. and S.V. Shah Acute Renal Failure. ACP Medicine 2005.
  • Pannu, N. et. al Prophylaxis Strategies for Contrast Induced Nephropathy JAMA. 2006;295:2765-2779