Acute Kidney Injury Flashcards Preview

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Flashcards in Acute Kidney Injury Deck (26):
1

In acute kidney injury, there is a reduction in _____ resulting in ______ developing over days

GFR; azotemia

2

What are common causes of acute kidney injury?

Renal ischemia or toxins

3

How is kidney size affected in AKI?

Kidney size is usually preserved

4

What are some of the diagnostic criteria for AKI?

  • An abrupt (within 48 hours) reduction in kidney function defined as
    • An absolute increase in serum creatinine level of 0.3 mg/dl or
    • A percentage increase in serum creatinine level of ≥ 50% or
    • A reduction in urine output < 500 mL in 24 hours

5

Define the following:

  • Oliguria:
  • Azotemia:
  • Uremia:

  • Oliguria: Urin output < 400-500 ml/day
  • Azotemia: Elevation of nitrogen waste products related to insufficient filtering of blood by the kidneys
  • Uremia: The illness accompanying kidney failure which results from the toxic effects of abnormally high concentrations of nitrogenous substances in the blood

6

Serum creatinine levels are inversely proportionate to  ___

GFR

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7

What are the limitations of creatinine compared to inulin?

Unlike inulin, creatinine is also secreted in the nephron and creatinine clearance overestimates GFR

8

What is BUN and when is it used to diagnose renal disease?

Blood Urea Nitrogen - nitrogenous waste product of protein metabolism

Useful in conjunction with creatinine in the differential diagnosis of renal disease - less accurate than creatinine due to variation in protein intake, catabolic rate, and tubular reabsorption

9

How are casts formed and how do they present in acute tubular necrosis?

Casts are caused by the trapping of cellular elements in a matrix of protein secreted by renal tubules

Granular casts - muddy brown urine - are seen in cases of acute tubular necrosis

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10

Autoregulation of GFR and RBF is effective between the blood pressures of __ and __

80 and 160

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11

What GFR autoregulation mechanisms can compensate for decreased perfusion pressure?

Increased vasodilatory prostaglandins - dilate afferent arterioles

Increased angiotensin II - Constrict efferent arteriole

12

With impaired autoregulation _____ _____ has greater effect on GFR

arterial pressure

13

What are the three categories of AKI?

  • Pre-renal: imparied effective renal perfusion
  • Renal: intrinsic renal disease
  • Post renal: obstruction of urinary flow

14

Pre-renal AKI consists of decreased GFR without _____ or _____ injury to tubules

ischemic or nephrotoxic

15

How does pre-renal AKI lead to oliguria?

Decreased effective renal perfusion → increased Ang II and vasopressin → increased reabsorption of sodium (at proximal tubule) and water → concentrated urine → oliguria

16

Pre-renal AKI is associated with increased reabsorption of urea

Elevation of ____is out of proportion to creatinine?

elevation of BUN is out of proportion to creatinine (>20:1)

17

How does the tubular epithelium appear in pre-renal AKI?

normal

18

What is the most common cause of renal AKI?

Acute tubular necrosis

19

What are some causes of Renal AKI?

  • ATN
  • Inflammation: glomerulonephritis, tubulointerstitial nephritis, vasculitis
  • Embolism, thrombosis, thrombotic miroangiopathy
  • Neoplasms: infiltrating tumors

20

What are some morphologic features of acute tubular necrosis (ATN)?

  • Tubular dilation
  • Attenuation of tubular epithelium
  • Loss of epithelial cell brush border
  • Granular cast material
  • Mitotic figures (regenerative change)

21

How do tubules regenerate after ATN?

Sublethally injured tubular epithelial cells repopulate the tubules by:

De-differentiation → proliferation → migration → re-establishing cell polarity

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22

What are some causes of Post-renal AKI?

Bladder outlet obstruction

Ureteral obstruction

23

How many kidneys are affected in Post-Renal AKI?

both

24

What is hydronephrosis (in post renal AKI)?

Distension and dilation of the renal pelvis calyces

25

How can fractional excretion of sodium (FENa) distinguish pre-renal AKI from acute tubular necrosis?

  • In the setting of volume depletion urine Na reabsorption should be increased in the proximal tubules → FENa < 1%
  • If the proximal tubules are injured (ATN), sodium reabsorption will be impaired → FENa > 2%

26

How do you calculate FENa?

FENa = [(UNa x PCr)/ (PNa x Ucr)] x 100

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