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USMLE Step 3 MTB > Nephrology > Flashcards

Flashcards in Nephrology Deck (241)
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1

first step in evaluating renal failure

1. PRErenal (perfusion)
2. RENAL (parenchymal)
3. POSTrenal (drainage)

2

clues renal failure is ACUTE

1. normal kidney size
2. normal hematocrit
3. normal Ca2+

3

clues renal failure is CHRONIC

1. smaller kidneys
2. renal failure of more than 2 weeks will drop Hct (decreased erythropoietin production)
3. Ca2+ levels drop (decreased vitamin D hydroxylation)

4

causes of PRErenal azotemia

- ANY cause of hypOperfusion

- hypOtension (SBP less than 90)
- hypOvolemia (dehydration or blood loss)
- low oncotic pressure (low albumin)
- CHF (heart can't PUMP)
- constrictive pericarditis (heart can't FILL)
- RAS

5

characteristic diagnostic tests for PRErenal azotemia

- BUN:Cr ratio of more than 15:1, and often more than 20:1
- LOW urinary Na+ (less than 20)
- urine osmolality more than 500
- may have hyaline casts on UA

6

treatment for PRErenal azotemia

treat UNDERLYING cause

7

mechanism of BUN elevation in PRErenal azotemia

low volume status, increases ADH, and ADH increases urea transporter activity in collecting duct

8

causes of POSTrenal azotemia (postobstructive uropathy)

- stones
- strictures
- cancer
- neurogenic bladder (MS or DM)

9

BUN:Cr ratio seen in POSTrenal azotemia

also more than 15:1

10

clues to obstructive uropathy

- distended bladder on exam
- large volume diuresis after Foley catheter placement
- B/L hydronephrosis on US

11

what must be true in order for postobstructive uropathy to cause renal failure?

MUST BE BILATERAL

(UNIlateral obstructive cannot cause renal failure)

12

INTRArenal causes of renal failure

- ATN (acute tubular necrosis)
- AGN (acute glomerulonephritis)
- AIN (acute interstitial nephritis)

13

causes of ATN (acute tubular necrosis)

- either hypOperfusion or toxic injury

- surgery
- severe burns

- aminoglycosides/amphotericin/contrast/chemotherapy
- rhabdomyolysis

14

causes of AGN (acute glomerulonephritis)

(name 11)

- Goodpasture's syndrome
- Churg-Strauss syndrome
- Wegener's granulomatosis
- polyarteritis nodosa
- IgA nephropathy (Berger's disease)
- Henoch-Schonlein purpura
- poststreptococcal glomerulonephritis
- cryoglobulinemia
- lupus nephritis
- Alport syndrome
- TTP/HUS

15

causes of AIN (acute interstitial nephritis)

- antibiotics
- NSAIDs
- infection (e.g. Streptococcus, viral, Legionella)

16

characteristic diagnostic tests for INTRArenal renal failure

- BUN:Cr ratio of 10:1
- urinary sodium more than 40
- urine osmolality less than 350

17

how many days of use does it usually take for aminoglycosides to cause kidney damage?

4-5 days

18

mechanism of rapid onset of renal failure with contrast agent

- directly toxic to kidney tubules

- also, causes intense vasoconstriction of Afferent arterioles (decreased perfusion)

(hypOperfusion = LOW urine sodium)

19

what does UA show in ATN?

"muddy brown," or granular casts

20

treatment for ATN

NO specific therapy

21

adverse effect of cyclophosphamide

hemorrhagic cystitis

22

cause of renal failure from rhabdomyolysis

direct TOXIC effect of MYOGLOBIN on kidney tubule

23

causes of rhabdomyolysis

- crush injury
- seizure
- cocaine toxicity
- prolonged immobility
- hypOkalemia resulting in muscle necrosis
- recent initiation of STATIN

24

best INITIAL test for rhabdomyolysis

UA (large blood)

25

rhabdomyolysis labs:

- CPK level
- potassium level
- calcium level
- serum bicarbonate level

- ELEVATED CPK
- hypERkalemia
- hypOcalcemia
- decreased bicarb

26

MOST ACCURATE test for rhabdomyolysis

urine myoglobin

27

mechanism of hypOcalcemia in rhabdomyolysis

damaged sarcolemma outside of SER can bind as much Ca2+ as it wants

28

treatment for rhabdomyolysis

1. NS bolus
2. mannitol (decrease contact time of myoglobin with the tubules)
3. alkalinization of urine (decreases precipitation of myoglobin in the tubules)

29

suicide by antifreeze ingestion (ethylene glycol)

HAGMA

oxalate crystals

30

best INITIAL test for ethylene glycol poisoning

UA (envelope-shaped oxalate crystals)