Updated: 11/10/2020

Acute Kidney Injury

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Snapshot
  • A 56-year-old man presents with lower abdominal pain. His symptoms have progressively worsened over the course of the day. Medical history is significant for benign prostatic hyperplasia on tamsulosin. His blood pressure is 144/106 mmHg (normally, his blood pressure is 120/80 mmHg). On physical examination he has bladder distension. Laboratory testing is significant for a creatinine of 2.4 mg/dL (last serum creatinine was 0.7 mg/dL.) (Post-renal acute kidney injury likely secondary to benign prostatic hyperplasia)
Introduction
  • 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
    • postrenal causes
      • urinary flow obstruction (e.g., benign prostatic hyperplasia and nephrolithiasis)
  • 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
Presentation
  • Symptoms
    • may be asymptomatic
    • oliguria
    • anuria
    • polyuria
    • confusion
  • Physical exam
    • hypertension
    • edema
    • decreased urine output
Imaging
  • Renal ultrasound
    • indication
      • initial imaging study for assessing acute kidney injury
        • can assess for renal size and hydronephrosis
        • to assess for postrenal obstruction
Studies
  • 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)
Studies
Prerenal AKI   Intrarenal AKI
Postrenal AKI
Urine osmolality (mOsm/kg)
  • > 500
  • < 350
  • < 350
FeNa 
  • < 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
 
Differential
  • Acute gastrointestinal bleeding
  • Rhabdomyolysis
  • Medication-induced impairment of creatinine secretion
    • cimetidine
    • trimethoprim
    • pyrimethamine
Treatment
  • 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
Complications
  • Hyperkalemia
  • Metabolic acidosis
  • Uremic encephalopathy and platelet dysfunction
  • Anemia
  • Chronic kidney disease
 

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(M1.RL.13.27) A previously healthy 9-year-old, Caucasian girl presents to your office with severe abdominal pain. Her mother also mentions that she has been urinating significantly less lately. History from the mother reveals that the girl suffers from acne vulgaris, mild scoliosis, and had a bout of diarrhea 3 days ago after a family barbecue. Lab work is done and is notable for a platelet count of 97,000 with a normal PT and PTT. The young girl appears dehydrated, yet her serum electrolyte levels are normal. What is the most likely etiology of this girl's urinary symptoms? Tested Concept

QID: 100981
1

Hypothalamic dysfucntion

3%

(1/33)

2

Surreptitious laxative use

9%

(3/33)

3

Toxic shock syndrome

0%

(0/33)

4

Shiga toxin production from Shigella

12%

(4/33)

5

Shiga-like toxin production from EHEC

73%

(24/33)

M 1 E

Select Answer to see Preferred Response

(M1.RL.12.71) A 49-year-old female with a history of alcoholism was found lying unconscious on a bench at a local park and rushed to the emergency department. Upon arrival, the patient regained consciousness and complained of intense bilateral flank pain and a recent decrease in urination. Urine microscopy demonstrated abundant square crystals of calcium oxalate that looked like “folded envelopes." Which of the following findings is most likely to be seen in this patient: Tested Concept

QID: 101025
1

Metabolic alkalosis

19%

(7/36)

2

Anion gap metabolic acidosis

61%

(22/36)

3

Non-anion gap metabolic acidosis

11%

(4/36)

4

Respiratory acidosis

6%

(2/36)

5

Respiratory alkalosis

0%

(0/36)

M 2 D

Select Answer to see Preferred Response

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