24 – Urinary I

Question 1

What are the main determinants of GFR?

Answer 1

• Renal blood flow
• Hydraulic permeability of the capillaries
• Capillary surface area
• Net filtration pressure determined by Starling forces

Question 2

What are the indications for determining the combined or individual kidney GFR?

Answer 2

• To evaluate for suspected renal insufficiency
• To assess the function of each kidney if nephrectomy of 1 kidney is indicated
• To establish baseline measurements prior to use of a potentially nephrotoxic drug

Question 3

Clearance

Answer 3

• Clearance of substance X = GFR only if substance X is freely filtered, no reabsorption or secretion
  o And if not synthesized or metabolized in the body
• Ex. inulin=gold standard, but not used much anymore

Question 4

What are the methods to determine GFR?

Answer 4

• Plasma clearance methods
  o Endogenous or exogenous creatinine clearance
  o Iohexol clearance
  o Clearance of nuclear isotopes: DTPA
• Imaging
  o Nuclear scintigraphy
  o CT with iohexol contrast and special software

Question 5

What is a clinical surrogate to determine GFR?

Answer 5

• Rely on detection and trending of azotemia
  o Localization is important (pre-renal, renal, post-renal)
• *use history, PE, USG, and knowledge of hydration status
• Always try get a urine sample

Question 6

What is the difference between azotemia and uremia?

Answer 6

• Azotemia is a lab abnormality, uremia is a clinical syndrome

Question 7

Azotemia

Answer 7

• Lab finding on blood work
• Elevated concentrations of nitrogenous waste (BUN and creatinine) in the blood
• Many renal and non-renal causes
• *could see all 3 types of azotemia in the same patient

Question 8

Uremia

Answer 8

• Clinical syndrome
• Constellation of C/S and biochemical abnormalities
• May or may not be caused by renal disease
• *all uremic animals are azotemic, but NOT all azotemic animals are uremic

Question 9

Urea

Answer 9

• Nitrogenous waste product formed by ammonia
• Synthesized in liver from NH3
• Diffuses throughout all fluid compartments
• *kidneys are MAIN route of EXCRETION
• *Urea recycling is very important for helping maintain the medullary concentrating gradient
• Measurement provides crude index of renal function

Question 10

What will increase BUN?

Answer 10

• Any abnormality that decreases GFR
  o Pre-renal, renal, post-renal
• Diet, liver disease, GI bleeding, drugs that increase protein catabolism

Question 11

Creatinine

Answer 11

• Non-protein nitrogenous waste product
• Formed from nonenzymatic metabolic of creatine and phosphocreatine in muscle
• Kidneys are major route of excretion
• *crude index of GFR but better than BUN in most cases b/c is affected by fewer nonrenal variables

Question 12

Pre-renal azotemia

Answer 12

• Usually a consequence of reduced renal perfusion
• Look for c/s compatible with dehydration
  o Azotemic USG >1.030 dog, >1.035 cat
• Try get a urine sample before starting IV fluids

Question 13

Renal azotemia

Answer 13

• Due to renal failure or disease
• Implies >75% of nephrons are nonfunctional
• Azotemia with DILUTE USG <1.030 dogs, <1.035 cats
• Exceptions: patients with other long-standing causes of PU/PD leading to medullary washout and some cats with CKD

Question 14

Post renal azotemia

Answer 14

• Due to obstruction in excretory outflow tract or from uroabodomen
• Degree of azotemia and USG are variable, but clinical findings are suggestive

Question 15

How do you treat a blocked cat?

Answer 15

• IV fluids: at least 50% shock dose
• Unblock the cat with or without sedation
• Treatment for hyperkalemia
  o Calcium gluconate
  o Bicarbonate
  o Insulin
  o Glucose
  o Dialysis

Question 16

SDMA

Answer 16

• Test done by Idexx
• Relies primarily on renal elimination for excretion
  o Circulating concentrations are primary affected by changes in GFR and therefore correlate to kidney function
  o May find changes with 40% reduction (so when 60% impaired neurons compared to 75%)
• NOT affected by muscle mass

Question 17

Acute renal failure

Answer 17

• Azotemia caused by renal parenchymal disease or injury that overs hours to days
• Potentially reversible
• Acute onset
• Oliguria/anuria
• Azotemia and NOT concentrating urine if producing urine
• Generally not anemic and in good body condition
• *previously normal renal function

Question 18

What are common causes of acute renal failure?

Answer 18

• Nephrotoxins
• Infectious causes
• Ischemia

Question 19

Chronic renal failure

Answer 19

• Azotemia caused by renal disease or injury that has occurred over a PROLONGED duration
• Irreversible and progressive
• Slow insidious clinical onset unless acute on chronic crisis
• PU/PD
• Progressive azotemia and eventual uremia
• Anemia, poor body condition
• Small and irregular kidneys
• Diverse etiologies
• Commonly see diminished urine concentrating ability
  o Isothenuria or hyperthenuric
  o NOT baruric or hyposthenuria

Question 20

Renal secondary hyperparathyroidism

Answer 20

• Subclinical or clinical syndrome
• Pathogenesis is controversial
• Involves
  o Hyperphosphatemia: decreased excretion
  o Low circulating levels of Vit D
  o Skeletal resistance to PTH
• Young animals more predisposed: growing and have more mineral movement