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Nephrology USMLE Step 3 > Section 1: Acute Renal Failure > Flashcards

Section 1: Acute Renal Failure Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the first step in managing a patient with acute renal failure (ARF)?

A

The first step is to evaluate whether the renal failure is:

  • Prerenal (perfusion)
  • Renal (parenchymal)
  • Postrenal (drainage).

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

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2
Q

List the clues to a renal failure being of short duration

A
  • Normal kidney size
  • Normal hematocrit
  • Normal calcium level

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

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3
Q

List the effects of chronic renal failure

A
  • It makes the kidneys smaller
  • With renal failure of more than 2 weeks, the hematocrit will drop from loss of erythropoietin production
  • Calcium levels drop from the loss of vitamin D hydroxylation (i.e., activation)

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

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4
Q

Causes of Prerenal Azotemia

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

A

Any cause of hypoperfusion will lead to renal failure:

  • Hypotension, generally with a systolic pressure < 90 mm Hg
  • Hypovolemia from dehydration or blood loss
  • Low oncotic pressure (low albumin)
  • Congestive heart failure
  • Constrictive pericarditis
  • Renal artery stenosis

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

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5
Q

Diagnostic testing in prerenal azotemia

A
  • BUN to creatinine ratio of > 15: 1 and often > 20: 1
  • Urinary sodium is low (< 20)
  • Fractional excretion of sodium < 1 percent: This is largely the same thing as a low urine sodium. Do not spend your time learning to do the calculation.
  • Urine osmolality > 500
  • May have hyaline casts on urinalysis

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7535-7562). . Kindle Edition.

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6
Q

Rx of prerenal azotemia

A

Based on underlying cause

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7
Q

List the tests to be ordered on CCS for all renal cases

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7567-7570). . Kindle Edition.

A
  • Urinalysis
  • Chemistries
  • Renal ultrasound

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7567-7570). . Kindle Edition.

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8
Q

List the causes of postrenal azotemia (obstructive uropathy)

A
  • Stones in the bladder or reters
  • Strictures
  • Cancer of the bladder, prostate, or cervix
  • Neurogenic bladder (atonic or noncontracting, such as from multiple sclerosis or diabetes)

Remember: The obstruction must be bilateral to cause renal failure. Unilateral obstruction cannot cause renal failure

Obstructive uropathy will give an elevated BUN-to-creatinine ratio of > 15: 1, similar to that seen in prerenal azotemia

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

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9
Q

List the clues to obstructive uropathy

A
  • Distended bladder on exam
  • Large volume diuresis after passing a urinary catheter
  • Bilateral hydronephrosis on ultrasound

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

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10
Q

Causes of intrarenal renal failure

A

Acute tubular necrosis (ATN)

Medications

Rhabdomyolysis

Crystals

Contrasts

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

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11
Q

Clues to intrarenal renal failure

A
  • BUN-to-creatinine ratio closer to 10: 1
  • Urinary sodium > 40
  • Urine osmolality < 350

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

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12
Q

True or False:

Acute tubular necrosis (ATN) can be caused by either hypoperfusion to the point of death of the tubular cells or by various toxic injuries to the kidney. It is often caused by a combination of both.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

A

True

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13
Q

Causes of toxin-induced renal insufficiency

A
  • Aminoglycosides, such as gentamicin, tobramycin, or amikacin: Hypomagnesemia is suggestive of aminoglycoside-induced renal failure, but it is not conclusive.
  • Amphotericin
  • Contrast agents
  • Chemotherapy, such as cisplatin

The urinalysis may show “muddy brown” or granular casts.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7574-7609). . Kindle Edition.

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14
Q

A man is admitted for pneumonia from a nursing home. He is placed on piperacillin-tazobactam, and he becomes afebrile. Two days later, his BUN and creatinine start to rise. He develops a new fever and a rash.

What is the most likely diagnosis?

What is the best initial test?

What is the most accurate diagnostic test?

Rx?

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7601-7612). . Kindle Edition.

A

Allergic interstitial nephritis is a hypersensitivity reaction to medications such as penicillin or sulfa drugs. Other common culprits are phenytoin, allopurinol, cyclosporine, quinidine, quinolones, or rifampin.

The clue to the diagnosis is the fever and rash.

The best initial test is a urinalysis (UA) that shows white cells. However, the UA is not capable of distinguishing between neutrophils and eosinophils

The most accurate test is a Wright stain or Hansel’s stain of the urine that will show eosinophils. This is more sensitive than either the blood eosinophil level or an elevated IgE level.

There is no specific therapy generally given for allergic interstitial nephritis; it resolves on its own

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7601-7612). . Kindle Edition.

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15
Q

True or False

Cyclophosphamide causes hemorrhagic cystitis, not renal failure.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7601-7612). . Kindle Edition.

A

True

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16
Q

List the causes of allergic interstitial nephritis

A

Hypersensitivity reaction to medications such as:

  • Penicillin
  • Sulfa drugs
  • Phenytoin
  • Allopurinol
  • Cyclosporine
  • Quinidine
  • Quinolones
  • Rifampin

Use “PRACQS”

17
Q

In cases of rhabdomyolysis, large-volume muscular necrosis is associated with renal failure from the direct toxic effect of myoglobin on the kidney tubule.

List the causes of rhabdomyolysis

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7614-7630). . Kindle Edition.

A
  • Crush injury
  • Seizure
  • Prolonged immobility in an intoxicated patient
  • Hypokalemia resulting in muscle necrosis
  • A patient recently started on a “statin” medication for hyperlipidemia

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7614-7630). . Kindle Edition.

18
Q

Rhabdomyolysis

  • Best initail test
  • Most accurate test
  • Other important test finding
A

Urinalysis showing dipstick positive for large amounts of blood with no cells seen on the microscopic examination

Urine myoglobin is probably the single most accurate test.

CPK will be elevated

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7614-7630). . Kindle Edition.

19
Q

Tests to order on CCS for rhabdomyolysis

A
  • Potassium level (hyperkalemia): Potassium goes up from any cellular destruction, such as from a tumor lysis, hemolysis, or rhabdomyolysis
  • Calcium level (hypocalcemia): Why the calcium level is decreased in rhabdomyolysis is not clear. Damaged muscle may bind increased amounts of calcium. Hyperphosphatemia may lead to binding of calcium with the phosphate
  • Chemistries especially for detecting a decreased serum bicarbonate
20
Q

Rx for rhabdomyolysis

A
  • Bolus of normal saline
  • Mannitol and diuresis to decrease the contact time of myoglobin with the tubule
  • Alkalinization of the urine may decrease precipitation of myoglobin at the tubule

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7631-7633). . Kindle Edition.

21
Q

A patient is brought to the emergency department after a seizure leading to prolonged immobility on a sidewalk. He has dark urine and myalgias. What is the most urgent step in the management of this patient?

a. Urinalysis
b. Urine myoglobin level
c. EKG
d. CPK level
e. Phosphate level
f. Creatinine

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7634-7656). . Kindle Edition.

A

C. EKG is the most urgent step in an acute case of rhabdomyolysis. This case tests your knowledge of how people die with rhabdomyolysis. Severe muscle necrosis leads to hyperkalemia, which leads to arrhythmia. If this is a CCS case, then all of the tests should be done simultaneously. A specific diagnosis with urinalysis or urine myoglobin is not as important as detecting and treating potentially life-threatening conditions, such as hyperkalemia with peaked T waves. This condition would be treated with immediate intravenous calcium gluconate, insulin, and glucose.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7634-7656). . Kindle Edition.

22
Q

Crystal-induced renal failure can result from oxalate crystals or uric acid crystals. For oxalate crystals look for suicide by antifreeze ingestion (ethylene glycol). The patient will be intoxicated, and have metabolic acidosis with an elevated anion gap

  • Best initial test
  • Best initial treatment

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7634-7656). . Kindle Edition.

A
  • Urinalysis showing envelope-shaped oxalate crystals
  • Fomepizole or ethanol with immediate dialysis

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7634-7656). . Kindle Edition.

23
Q

Uric acid induced renal failure (insufficiency) is usually due to tumor lysis syndrome, most often due to chemotherapy for lymphoma.

What is the Rx?

A

Hydration and allopurinol

24
Q

What is the best method to prevent contrast induced renal failure?

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7665-7668). . Kindle Edition.

A

Give hydration with normal saline and possibly bicarbonate, N-acetyl cysteine, or both.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7665-7668). . Kindle Edition.

25
Q

List the effects of NSAIDs on the kidney

A
  • Direct toxicity and ATN
  • Allergic interstitial nephritis with eosinophils in the urine
  • Nephrotic syndrome
  • Afferent arteriolar vasoconstriction and decreased perfusion of the glomerulus, worsening renal function

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kindle Locations 7674-7683). . Kindle Edition.

Nephrology USMLE Step 3 (5 decks)

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