12.2: Acute renal failure

Question 1

What are the two hallmark s/sx of acute renal failure?

Answer 1

Azotemia with oliguria

Question 2

What are the three major divisions of acute renal failure?

Answer 2

• Prerenal
• Intrarenal
• Post renal

Question 3

How do you diagnose azotemia?

Answer 3

Increase in BUN and Cr

Question 4

What is the cause of prerenal azotemia?

Answer 4

Decreased blood flow to the kidneys

Question 5

What are the s/sx of prerenal azotemia?

Answer 5

• Decreased GFR
• Azotemia
• Oliguria

Question 6

What is the BUN:Cr ratio with prerenal azotemia? Why does this occur?

Answer 6

• more than 15
• Cr is not reabsorbed, but BUN is. When there is an increase in renin, there is increased Na and BUN reuptake from the tubule, but not Cr. Thus the ratio increases

Question 7

What are the two measures that indicate good tubule function? What happens to these with prerenal azotemia?

Answer 7

• FENa (fractional excretion of Na) = less than 1%
• urine osm more than 500

-These are normal (above) with prerenal azotemia

Question 8

What are the signs of postrenal azotemia?

Answer 8

Decreased GFR, azotemia and oliguria

Question 9

What causes the early rise in BUN:Cr ratio with POSTrenal azotemia? Why does it decrease later on?

Answer 9

Back pressure from blocked outflow increases hydro static pressure in the tubule, and increased BUN reabsorption

Tubular damage ensures and decreases BUN resorption

Question 10

What happens to FENa and Urine osm with postrenal azotemia? Early Post Renal? Late posternal?

Answer 10

Early= Both remain intact (FEN less than 1% and urine osm more than 500

Late post-renal = tubular damage, leading to higher FENa, and lower urine osmolality

Question 11

What is the most common cause of acute renal failure?

Answer 11

Acute tubular necrosis

Question 12

What is acute tubular necrosis? What happens to GFR? Why? What appears in the urine?

Answer 12

Injury and necrosis of the tubular epithelium. Necrotic cells plug tubules to decrease GFR.

Brown, granular casts appear in the urine

Question 13

Brown, granular casts in the urine = ?

Answer 13

Acute tubular necrosis

Question 14

What are the major histological findings of acute tubular necrosis?

Answer 14

Loss of tubular epithelial nuclei and lumen, detachment of epithelial cells from BM

Question 15

What happens to the following with acute tubular necrosis:

• BUN:Cr
• FENa
• Urine [c]

Answer 15

• Decreased BUN:Cr (less than 15)
• Increase FENa (more than 2%)
• osm less than 500

Question 16

What are the two major etiologies of acute tubular necrosis?

Answer 16

Ischemic

Nephrotoxic

Question 17

What parts of the nephron are particularly susceptible to ischemia?

Answer 17

Proximal tubule and medullary segment of the thick ascending limb

Question 18

What causes nephrotoxic ATN? Which part of nephron is particularly susceptible?

Answer 18

Toxic agents cause necrosis of tubules

Proximal tubule

Question 19

What are the toxic agents that can cause toxic ATN? (abx, environmental toxin, crush injury, automobile fluid type, radiology things?

Answer 19

• Aminoglycosides
• Heavy metals
• Myoglobinuria
• Ethylene glycol
• Radiocontrast dye

Question 20

Oxalate crystals in the urine is suspicious for what type of poisoning?

Answer 20

Ethylene glycol

Question 21

What produces urate to cause ATN?

Answer 21

Tumor lysis syndrome

Question 22

What are the two measures to ensure that chemo does not induce ATN via tumor lysis syndrome?

Answer 22

• IVF to dilute urate

- Allopurinol

Question 23

What are the urinary findings of ATN? (2)

Answer 23

• Oliguria

- Brown, granular casts

Question 24

What happens to BUN and Cr with ATN?

Answer 24

Increases

Question 25

What metabolic disturbance is seen with ATN? What causes this?

Answer 25

Hyperkalemia with metabolic acidosis - Hyperkalemia from decreased K excretion - Acidosis from decreased excretion of organic acids

Question 26

What is the calculation for anion gap?

Answer 26

Na - (Cl + HCO3)

Question 27

What is the treatment for hyperkalemia and acidosis 2/2 ATN? Will the necrotic tissues heal?

Answer 27

Dialysis Yes

Question 28

How long does it take for the necrotic tissue in ATN to regenerate? Why? What sign signifies healing?

Answer 28

2-3 weeks, since tubular cells are stable cells, and need time to reenter the cycle Increasing urine output

Question 29

What is acute interstitial nephritis?

Answer 29

Drug-induced HSR of the interstitium and tubules, resulting in intrarenal ARF

Question 30

What are the drugs that classically cause acute interstitial nephritis? (3)

Answer 30

- NSAIDs - PCN - Diuretics

Question 31

What are the histologic characteristics of interstitial nephritis?

Answer 31

Inflammation between the tubules, but relatively normal looking tubules

Question 32

What are the three major s/sx of interstitial nephritis?

Answer 32

- Oliguria - Fever - Rash

Question 33

What WBC can be seen in the urine with interstitial nephritis?

Answer 33

Eosinophils

Question 34

What is the treatment for interstitial nephritis?

Answer 34

Remove offending drug

Question 35

What can interstitial nephritis progress to?

Answer 35

Renal papillary necrosis

Question 36

Eosinophils in the urine = ?

Answer 36

Acute interstitial nephritis

Question 37

What are the s/sx of renal papillary necrosis?

Answer 37

Gross hematuria and flank pain

Question 38

What are the 4 major causes of renal papillary necrosis?

Answer 38

- Chronic analgesic use - DM - Sickle cell dz - Acute pyelonephritis