questions 4

Acute Kidney Injury

Topic updated on 09/23/17 7:58pm

  • A 54-year-old man is admitted to the cardiac care unit after coronary angiography and revascularization secondary to unstable agina. Approximately 1 week after the procedure he is found to have a "bluish" discoloration of the first and second digits of the foot. Laboratory testing is significant for an elevated serum creatinine. A urinalysis is benign. (Renal atheroemboli)
  • Clinical definition
    • acute reduction in glomerular filtration rate (GFR)
      • recall that GFR represents the sum of the filtration rates of nephrons
        • therefore, GFR reflects functioning renal mass
  • Epidemiology
    • risk factors
      • hypertension
      • chronic kidney disease
      • dehydration and volume depletion
      • diabetes
      • chronic liver or lung disease
  • Etiology
    • prerenal causes
      • decreased renal perfusion (e.g., hemorrhage, congestive heart failure, and diuretic use)
    • intrarenal causes
      • acute tubular necrosis
        • ischemia and toxic causes
      • interstitial nephritis
      • glomerulonephritis
      • vasculitis
      • hemolytic uremic syndrome
      • cholesterol emboli
    • postrenal causes 
      • urinary flow obstruction (e.g., benign prostatic hyperplasia and nephrolithiasis)
      • post-operative secondary to bladder manipulation and anesthesia
        • bladder scans should be performed followed by urinary catheterization
  • Pathogenesis
    • based upcome etiology (look at etiology)
  • Prognosis
    • lower rates of recovery in patients > 65 years of age
    • increased risk of end-stage renal disease, chronic kidney disease, and mortality
  • Symptoms
    • may be asymptomatic
    • oliguria
    • anuria
    • polyuria
    • confusion
  • Physical exam
    • hypertension
    • edema
    • decreased urine output
  • Renal ultrasound
    • indication
      • initial imaging study for assessing acute kidney injury
        • can assess for renal size and hydronephrosis
        • to assess for postrenal obstruction
  • Labs
    • increase in serum creatinine by ≥ 0.3 mg/dL within 48 hours
    • blood urea nitrogen (BUN):creatinine ratio
    • urinalysis
      • dipstick
        • to assess for protein, glucose, leukocyte esterase, hemoglobin and myoglobin, and specific gravity
      • microscopy
        • for example
          • red dysmorphic cells suggests a glomerular etiology (e.g., glomerulonephritis)
          • muddy brown casts suggests tubular necrosis
          • white blood cell casts suggest pyelonephritis or acute interstitial nephritis
    • fractional excretion of Na+ (FeNa+)
      • if patient is on diuretics use FeUrea
    • urine osmolality and Na+
Studies To Assess For Prerenal, Intrarenal, and Postrenal Acute Kidney Injury (AKI)
Prerenal AKI Intrarenal AKI
Postrenal AKI
Urine osmolality (mOsm/kg)
  • > 500
  • < 350
  • < 350
  • < 1%
  • > 2%
  • < 1% in mild cases
  • > 2% in severe cases
Urine Na+ (mEq/L)
  • < 20
  • > 40
  • > 40
Serum BUN/Cr
  • > 20:1
  • < 15:1
  • Variable
  • Acute gastrointestinal bleeding
  • Rhabdomyolysis
  • Medication-induced impairment of creatinine secretion
    • cimetidine
    • trimethoprim
    • pyrimethamine
  • Treatment is dependent on the etiology of AKI and its consequences
    • for example
      • a patient who is hyperkalemic and not responding to medical treatment should be dialyzed
      • a patient with a history of excessive fluid loss (e.g., diarrhea and vomiting) should be given intravenous fluid
  • Hyperkalemia
  • Metabolic acidosis 
  • Uremic encephalopathy and platelet dysfunction
  • Anemia
  • Chronic kidney disease


Qbank (1 Questions)

(M2.RL.4754) A 69-year-old male presents to the emergency department for sudden shortness of breath that came on while he was sleeping. He currently is short of breath, but denies any chest pain, arm pain, or jaw pain. The patient has a past medical history of hypertension, obesity, diabetes, and GERD. The patient states he has not filled his prescriptions for any of his medications in months and cannot remember what his medications are. An EKG is performed and is seen in Figure A. A chest radiograph is obtained and is seen in Figure B. Lab values at admission are below:

Na+: 139 mEq/L
K+: 4.0 mEq/L
Cl-: 100 mEq/L
HCO3-: 24 mEq/L
BUN: 22 mg/dL
Glucose: 72 mg/dL
Ca2+: 9.9 mg/dL
Mg2+: 1.5 mEq/L
Creatinine: 0.9 mg/dL

The patient is started on appropriate treatment and his symptoms resolve. He is recovering on the medicine floor. His laboratory values are ordered and are below:

Na+: 137 mEq/L
K+: 3.5 mEq/L
Cl-: 100 mEq/L
HCO3-: 26 mEq/L
BUN: 39 mg/dL
Glucose: 70 mg/dL
Ca2+: 9.7 mg/dL
Mg2+: 1.5 mEq/L
Creatinine: 1.5 mg/dL

The patient states that he has not urinated in the past 24 hours. Which of the following is the most likely cause of this patient's current presentation? Topic Review Topic
FIGURES: A   B        

1. Furosemide
2. Intrarenal kidney injury
3. Urinary tract obstruction
4. Chronic kidney disease
5. Cholesterol emboli

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Cooper BA, Branley P, Bulfone L, Collins JF, Craig JC, Fraenkel MB, Harris A, Johnson DW, Kesselhut J, Li JJ, Luxton G, Pilmore A, Tiller DJ, Harris DC, Pollock CA; IDEAL Study.
N Engl J Med. 2010 Aug 12;363(7):609-19. PMID: 20581422 (Link to Pubmed)
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