Updated: 11/30/2021

Acute Kidney Injury

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  • Snapshot
    • 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)
  • summary
    • 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
    • Pathogenesis
      • based upcome etiology (look at etiology)
  • 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
  • Presentation
    • Symptoms
      • may be asymptomatic
      • oliguria
      • anuria
      • polyuria
      • confusion
    • Physical exam
      • hypertension
      • edema
      • decreased urine output
  • Differential
    • Acute gastrointestinal bleeding
    • Rhabdomyolysis
    • Medication-induced impairment of creatinine secretion
      • cimetidine
      • trimethoprim
      • pyrimethamine
  • 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 AKIIntrarenal 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
  • 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
    • Elevated troponin
      • due to decreased renal clearance of the troponin
  • Prognosis
    • lower rates of recovery in patients > 65 years of age
    • increased risk of end-stage renal disease, chronic kidney disease, and mortality
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Questions (5)

(M2.RL.17.84) A 63-year-old man undergoes uncomplicated laparascopic cholecystectomy for acute cholecystitis and is admitted to the surgical ward for postoperative management. On postoperative day 1, routine laboratory studies reveal an increase in serum creatinine to 1.46 mg/dL from 0.98 mg/dL before the operation; BUN is 37 mg/dL, increased from 18 mg/dL on prior measurement; K is 4.8 mEq/L and CO2 is 19 mEq/L. The patient has an indwelling urinary catheter in place, draining minimal urine over the last few hours. After ruling out urinary catheter obstruction, which of the following is the most appropriate next step in management?

QID: 104531

Obtain urinalysis

14%

(1/7)

Place a new urinary catheter

0%

(0/7)

Administer IV fluid bolus

57%

(4/7)

Obtain bilateral renal ultrasonography

29%

(2/7)

Initiate emergent hemodialysis

0%

(0/7)

M 7 C

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(M2.RL.15.42) A 70-year-old man was diagnosed two days ago with a myocardial infarction and underwent percutaneous coronary intervention to reperfuse his left anterior descending artery. Two days later his creatinine is noted to be elevated (despite being normal the day before) and he complains of a "rash" on his foot (Figure A). Which of the following would most likely be found in laboratory studies?

QID: 104489
FIGURES:

Hyponatremia

0%

(0/25)

Hypokalemia

0%

(0/25)

Granular urinary casts

48%

(12/25)

Elevated white blood count in urine

4%

(1/25)

Eosinophiluria

44%

(11/25)

M 6 E

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(M2.OMB.4870) A 75-year-old man presents to the emergency department with fatigue. He has had severe nausea, vomiting, and diarrhea for the past 3 days. Today, his wife noticed that he was confused. The patient has a history of coronary artery disease with a drug-eluting stent placed 1 year ago, obesity, hypertension, and dyslipidemia. He denies chest pain or dyspnea, but complains of diffuse abdominal pain. His temperature is 99.0°F (37.2°C), blood pressure is 100/60 mmHg, pulse is 105/min, and respirations are 22/min. Physical exam reveals a confused man with dry mucous membranes. His abdomen is diffusely tender to palpation. Laboratory studies are ordered and notable for the following:

Serum:
Na+: 147 mEq/L
Cl-: 112 mEq/L
K+: 3.5 mEq/L
HCO3-: 14 mEq/L
BUN: 80 mg/dL
Glucose: 100 mg/dL
Creatinine: 2.1 mg/dL
Troponin: 0.10 mcg/L (normal < 0.01 mcg/L)

An ECG is ordered and is pending. Which of the following is the most appropriate management of this patient's elevated troponin?

QID: 216358

Aspirin

0%

(0/0)

Aspirin, heparin, clopidogrel, and cardiac catheterization

0%

(0/0)

Metoprolol and aspirin

0%

(0/0)

Obtain a urinalysis and creatine phosphokinase level

0%

(0/0)

Ringer lactate bolus

0%

(0/0)

M 11

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