Diseases of the Renal System p873-916

Question 1

List some nephrotoxins.

6

Answer 1

Aminoglycosides
Pigment nephropathies
NSAIDs
Vitamin D
Heavy metals
Acorn poisoning

Question 2

Where in the kidney do aminoglycosides accumulate?

Answer 2

Proximal tubular epithelial cells

Question 3

What follows after a toxic dose of aminoglycosides accumulates in the epithelial cells?

Answer 3

Cellular metabolism is disrupted and tubular cell swelling, death and sloughing into the tubular lumen occurs.

Question 4

What electrolyte abnormality can drive the occurrence of amingoglycoside nephrotoxicity?

A) Hyponatremia
B) Hypomagnesemia
C) Hypokalemia
D) Hypochloremia

Answer 4

C) Hypokalemia, as well as low calcium intake, can cause decreased urine output, leading to nephrotoxicity.

Question 5

What are two common causes of pigment nephropathy?

Answer 5

Myoglobin pigment and hemoglobin

Question 6

What is the primary renal lesion caused by NSAID toxicity?

Answer 6

Medullary crest necrosis, leading to gross hematuria.

Question 7

How does the inhibition of prostaglandin production by NSAIDs lead to renal necrosis?

Answer 7

Prostaglandins play an important role in vasodilation when renal blood flow is decreased due to redistribution of cardiac output, in cases of dehydration. NSAID inhibition of PGI2 and PGE2 decreases the ability of these mediators to properly perfuse the cortical and medullary portion of the kidney.

Question 8

What heavy metals can cause nephrotoxicosis?

What is a chelating agent used in animals that have suspect toxicosis?

Answer 8

Mercury, cadmium, zinc, arsenic and lead can all be nephrotoxic, but are rare causes of renal failure in horses.

Dimercaperol is a chelating agent for heavy metals and can be given IM initially at 3 mg/kg, q6hr for the first day and then 1 mg/kg q6h for two or more additional days.

Question 9

What part of acorns can cause nephrotoxicity?

Answer 9

The immature leaves and green acorns cause more toxicity than the mature acorns, due to the higher levels of tannins. This toxicity is seen less in horses than cattle.

Question 10

What is the underlying cause of vasomotor acute renal failure?

Answer 10

Sustained marked hypotension or release of endogenous pressor agents can initiate hemodynamically mediated ARF.

Question 11

What are some risk factors for vasomotor ARF?

5

Answer 11

Sepsis, hemorrhagic shock, severe intravascular volume deficit, septic shock, coagulopathy

Question 12

Acute glomerulopathy should be considered in horses with severe ARF that do not have a primary predisposing disease leading to vasomotor ARF and have not been exposed to nephrotoxins. What are several bacterial agents that have been isolated in the rare cases of acute glomerulopathy?

Answer 12

E. coli O103:H2S and Streptococcus mitis

Question 13

Patients with what clinical signs should have ARF as a suspected diagnosis?

Answer 13

Marked depression, anorexia, failure to produce urine in 6-12 hours after initiating fluid therapy.

Question 14

List some biochemical changes that occur in ARF.

Answer 14

Hyponatremia, hypochloremia, hypocalcemia, azotemia with a BUN:creatinine ratio often less than 10:1

Question 15

What is the most important assessment of renal function?

Answer 15

Glomerular filtration rate

Question 16

How is GFR determined?

Answer 16

Timed urine collections or assessing plasma disappearance of several compounds (eg. radiolabled substances)

Question 17

When treating a horse with ARF, how is a patient characterized with oliguria?

Answer 17

If, after fluid treatment is initiated, a horse has not produced urine in 12-24 hours, oliguria is present.

Question 18

In patients with oliguria, what secondary side effects can occur?

Answer 18

Edema, noted in the conjunctiva; subcutaneous swelling of dependent areas tachypnea and altered mental states

Question 19

Blood pressure changes, especially those with vasomotor nephropathy, occur in patients with ARF. Which is more common, hypo or hypertension? What can be done to correct this problem?

Answer 19

Hypotension is seen in patients with ARF, and may not be corrected with just administration of large amounts of IV fluids. Extra vascular accumulation or third spacing can be the cause. Hypertonic saline, dobutamine or other pressor agents can be employed.

Question 20

Once a patient with ARF continues being oliguric, despite fluid resuscitation and restoration of systemic BP, what drug treatment should be initiated?

Answer 20

Furosemide, at 1 mg/kg, IV q2h. A CRI can be started as well, 0.12 mg/kg/h. If urination does not occur, mannitol or a dopamine infusion can be started.

Question 21

In the first 1-3 days of life, creatinine concentration in newborns foals is ___% higher than their dams.

A) 10-20
B) 20-30
C) 30-40
D) 40-50

Answer 21

C) 30-40%, likely related to inability of creatinine to equilibrate rapidly across placental membranes

Question 22

Are BUN levels typically high or low in foals, during the first few months of life?

Answer 22

BUN levels are typically low, due to the anabolic state of the growing foal.

Question 23

What is the most common bacterial pathogen causing renal abscesses in foals?

Answer 23

Actinobacillus equii

Question 24

Chronic renal failure in horses is irreversible, progressive process that can be divided by clinical and pathological findings into two broad categories. What are these?

Answer 24

1) Primary glomerular disease

2) Primary tubulointerstitial disease

Question 25

List some causes of CRF in horses.

3

Answer 25

Proliferative glomerulonephritis
Chronic interstitial nephritis
Pyelonephritis

Question 26

Proliferative glomerulonephritis results from deposition of what along glomerular nephritis?

Answer 26

Circulating immune complexes, which then activates complement and vasculitis.

Question 27

GFR in normal horses ranges from ____-____ mL/kg/min and if this value falls below ___ mL/kg/min, this is indicative of a decrease in GFR.

Answer 27

1.5-3.0 mL/kg/min and decreased GFR has a value of < 1.0 mL/kg/min

Question 28

List some clinicopathologic findings in horses with CRF.

Answer 28

Hyperkalemia
Hyponatremia
Hypochloremia
Hypercalciumia 
Moderate anemia

Question 29

Horses can develop PU/PD due to being Cushinoid. By what three mechanisms might this occur?

Answer 29

PU may occur due to glucosuria. The renal threshold in horses is approximately 150-175 mg/dL. Once this occurs, an osmotic diuresis is created.

PU may occur due to antagonism of ADH on the collecting ducts, by cortisol. (ADH is released through the posterior pituitary after release from the hypothalamus. It is released for a need to decrease urine production to conserve water, in times of dehydration, etc.)

Cushinoid horses may have an adenoma, which decreases ADH production, leading to central diabetes insipidus.

Question 30

Describe the two different types of diabetes insipidus.

Answer 30

Neurogenic - lack of secretion of ADH

Nephrogenic - lack of sensitivity to ADH, by collecting duct cells

Question 31

Renal tubular acidosis is a syndrome in horses that results in what biochem abnormalities?

Answer 31

Hyperchloremic metabolic acidosis with a normal anion gap; patient can also be moderately-severely hypokalemia

Question 32

Differentiate between type I and type II renal tubular acidosis in horses.

Answer 32

I - decreased distal excretion of H+ ions, leading to inability to produce acidic urine
II - decreased proximal tubular resorption of bicarbonate and increased loss of bicarbonate in the urine

Both of these lead to acidosis from decreased H+ excretion.

Question 33

What predisposes small ruminants to develop struvite uroliths?

Answer 33

A diet high in phosphorus (grain-based) can increase the development of struvite (magnesium ammonium phosphate hexahydrate). These grain eating animals also produce less saliva, which is a large source of phosphate loss. Therefore, the phosphorus in the diet is absorbed through the GI and eliminated through the kidneys.

A calcium:phosphorus ratio > 2:1 can also increase struvite stone formation.

Question 34

A small ruminant on a diet of lush pasture and/or alfalfa may have increased formation of which type of stone?

A) Struvite
B) Silica
C) Calcium carbonate
D) Apatite

Answer 34

C) Calcium carbonate, as well as carbon oxalate can be seen in animals fed large amounts of alfalfa and on lush pastures. Oxalate binds with calcium and causes it to not be absorbed through the GI. Increased urinary calcium excretion occurs.

Question 35

Enzootic hematuria is closely related to toxicosis caused by Pteridium. The carcinogenic compound ptaquiloside has a synergistic relationship with what virus to cause bladder tumors?

Answer 35

Bovine papilloma virus 2